Acute viral hepatitis 372
Clinical features 372
Pathological features 373
Evolution of the lesion 379
Differential diagnosis of acute hepatitis 379
Sequelae of acute hepatitis 381
Chronic viral hepatitis 381
Clinical features 381
Pathological features 382
Pathogenetic mechanisms 387
Multiple chronic viral infections 389
Differential diagnosis of chronic hepatitis 390
Semiquantitative scoring in chronic hepatitis 391
Individual types of viral hepatitis 396
The subject of this chapter is the pathological consequences of infection with hepatotropic viruses. These infections are responsible for hepatitis, which is generally classified by viral type ( Table 6.1 ). Viral hepatitis can also be identified by the duration of infection and the clinicopathological syndrome that develops ( Table 6.2 ). Although some pathological features are unique to the type of virus responsible for infection, many aspects of the pathological injury and clinical progression are common to multiple types of hepatotropic viral infection.
|Hepatitis A (HAV)||RNA picornavirus|
|Sporadic or epidemic occurrence with faecal-oral transmission, resulting in acute disease only|
|Hepatitis B (HBV)||DNA hepadnavirus|
|Sporadic or endemic occurrence through sexual, perinatal and parenteral transmission|
|Chronic disease persists in 5% of adults and up to 90% of infants.|
|Chronic infection is associated with hepatocellular carcinoma.|
|Hepatitis C (HCV)||RNA flavi-like virus|
|Sporadic occurrence with parenteral transmission|
|Perinatal and sexual spread are less common.|
|Chronic disease develops in 75–85% of persons infected. |
Cirrhosis is associated with hepatocellular carcinoma.
|Hepatitis D (HDV)||RNA-defective virus|
|Sporadic or endemic disease occurs as co-infection with HBV.|
|Transmission is parenteral and sexual.|
|Chronic disease is seen in patients with chronic HBV infection.|
|HDV worsens the clinical severity of HBV infection.|
|Hepatitis E (HEV)||RNA virus|
|Sporadic or epidemic occurrence; endemic in areas|
|Transmission is faecal-oral, resulting in acute disease. |
Chronic hepatitis is reported in immunosuppressed patients.
|Mortality rate is 25% in pregnant women.|
Acute viral hepatitis
Occurrence of acute viral hepatitis may be sporadic or epidemic. Transmission of disease is usually by the faecal-oral route through contaminated food or water. Alternatively, transmission may be through sexual contact or parenteral exposure, such as by intravenous drug use, blood transfusion or occupational needlestick exposure.
The acute infection is often subclinical and usually anicteric. If present, symptoms may be nonspecific and not readily identifiable as resulting from viral hepatitis. Typical symptoms include fatigue, anorexia and nausea in the early stages, followed by dark urine and jaundice with increasing severity and duration. Right upper quadrant abdominal pain or discomfort, arthritis, urticaria, pruritus and low-grade fever may be present. In patients without jaundice, the symptoms may be mistaken for gastrointestinal (GI) viral infection or another nonspecific viral syndrome.
The severity of acute viral hepatitis may vary from a mild asymptomatic infection to fatal acute liver failure. The latter is characterized clinically by the development, within 26 weeks of the onset of clinical illness, of abnormal coagulation with an international normalized ratio (INR) ≥1.5 and the presence of hepatic encephalopathy in a patient with no pre-existing liver disease (AASLD guideline) and pathologically by massive or severe bridging hepatocyte necrosis. The terms ‘fulminant hepatic failure’ and ‘subacute hepatitis’ or ‘subacute hepatic necrosis’ were used to describe serious injury developing before or after 8 weeks of illness. This distinction is currently used less now because it does not provide actionable prognostic information. Defining the cause of the acute hepatitis and the presence of comorbidities may link prognosis to a patient’s presentation. In patients with acute viral hepatitis, the surviving parenchyma may be characterized by varying degrees of regeneration. Nodular hyperplasia, two-cell-thick hepatocyte plates between sinusoids and mitotic figures within hepatocytes may indicate liver cell regeneration and a potential for recovery. Serum markers of patient prognosis in fulminant hepatic failure include alpha fetoprotein, Gc-protein and troponin levels. Additionally, measures of hepatic synthetic capacity such as factor VII and computed tomography-derived liver volume may also be prognostic. Death may result from complications of infection or renal failure rather than from hepatic synthetic dysfunction directly.
Portal hypertension and ascites are typically associated with chronic liver disease and rarely develop in patients with acute hepatitis. These complications, when they do occur in acute disease, may be the result of hepatocyte loss and consequent collapse of the sinusoidal network.
Acute viral hepatitis is typically characterized by injury to hepatocytes and is identified by a marked elevation of serum aminotransferase (transaminase) activities. Increases in serum transaminase values precede a rise in bilirubin and may peak before the development of jaundice. Jaundice, in the presence of significant elevation of transaminase values, indicates a severe degree of liver injury. Jaundice or icterus may persist at lower levels of serum bilirubin during recovery because of bilirubin that is conjugated to albumin in tissue, particularly if hyperbilirubinaemia has been prolonged. This bilirubin and albumin complex has been termed ‘delta bilirubin’. There may also be a decrease in hepatic synthesis of clotting factors that, if severe, is reflected in prolonged prothrombin time (PT) and elevated INR.
Cholestatic hepatitis is a clinical variant of acute viral hepatitis in which biliary dysfunction predominates. This syndrome is characterized by elevation of alkaline phosphatase (ALP) and bilirubin values with proportionately less elevation of transaminase levels. The cholestatic biochemical abnormalities may persist for weeks or months. The prognosis of this pattern of hepatic injury is generally favourable when not associated with prominent hepatocellular necrosis. Cholestatic viral hepatitis must be distinguished clinically from biliary obstruction by biliary imaging studies and from drug/toxin-induced liver injury by clinical history (see Table 6.2 ).
Acute viral hepatitis is characterized morphologically by a combination of inflammatory cell infiltration, macrophage activity, hepatocellular damage and regeneration. The proportion and detailed nature of these components vary widely according to the particular virus responsible, the host response and the passage of time. The pathological features are considerably different from those of classic acute inflammation in most other tissues, because they primarily represent a response of the patient’s immune system to viral antigens displayed on cells, rather than a vascular and cellular response to injury. Thus, neutrophil-rich infiltrates are not seen. Some features of acute inflammation are nevertheless present to a limited extent. For example, the liver in acute viral hepatitis is swollen and tender, its capsule is tense, and blood vessels are engorged.
Information on the macroscopic appearance of the liver in nonfatal acute hepatitis is mainly derived from laparoscopy and liver transplantation (LT). Initially the liver is swollen and red, its capsule oedematous and tense; exuded tissue fluid may be seen on the capsular surface. Focal depressions are the result of localized subcapsular necrosis and collapse. In patients with severe cholestasis, the colour of the liver is bright yellow or green. In fulminant hepatitis the organ shrinks and softens as a result of extensive necrosis, and the capsule becomes wrinkled. The left lobe may be more severely affected than the right. If the patient survives for weeks or months, tan to yellow-green nodules of regenerating parenchyma may be seen protruding from the capsular surface or deep within the liver ( Fig. 6.1 ), separated or surrounded by more haemorrhagic, or redder, necrotic areas. In other examples, necrosis is uniform throughout the organ. Of note, these nodules can be seen by radiographic imaging and at times are mistaken for cirrhosis, or even metastatic carcinoma, which could adversely affect the patient’s LT status.
Patients dying of acute liver failure often have damage to other organs, which may significantly contribute to the immediate cause of death. Findings at autopsy include pneumonia, septicaemia, cerebral oedema, GI haemorrhage and pancreatitis. Such lesions help to explain death when liver cell damage is limited in extent or there has already been substantial regeneration.
Light microscopy appearance: types of necrosis
The histological classification of acute hepatitis in this chapter is based on different patterns of hepatocellular necrosis. These patterns therefore are briefly reviewed before the microscopic changes of acute hepatitis are described in detail. More than one of the patterns of necrosis described next may be seen in different parts of the same liver and even within a single biopsy specimen.
Spotty (focal) necrosis and apoptosis
In the focal form of necrosis, which represents the fundamental lesion of acute viral hepatitis, individual hepatocytes within otherwise intact parenchyma die and are removed. The mode of death of hepatocytes probably includes both lytic necrosis and apoptosis (see Chapter 1 ), but the relative contribution of each may vary. In the case of apoptosis (or formation of acidophilic bodies), T lymphocytes likely play a role. Apoptotic hepatocytes are called ‘acidophil bodies’ because of their dark-red staining with eosin. (The name ‘Councilman bodies’ is generally used in the setting of yellow fever, as originally described by William Thompson Councilman.) The remnants of cells affected by either process are rapidly removed from the site by blood flow or phagocytosis. Clusters of pigment-laden macrophages are also frequently seen throughout the parenchyma in such cases, representing sites of phagocytosis of hepatocellular debris.
Confluent and bridging necrosis
The confluent type of necrosis involves groups of adjacent dead hepatocytes or the site where a group of hepatocytes has undergone previous necrosis and removal, so that areas of confluent necrosis are formed. These are often perivenular in location. Confluent necrosis linking vascular structures and portal zones is known as ‘bridging necrosis’. Bridging at the periphery of complex acini links terminal hepatic venules (central veins) to each other but does not involve portal tracts. This is called ‘central-central’ bridging in the lobular nomenclature. The other form of bridging necrosis links terminal hepatic venules to portal tracts (‘central-portal’ bridging). This form is best explained as necrosis of zone 3 of the simple acinus, as described by Rappaport, because this zone touches both terminal hepatic venule and portal tract. Zone 3 bridges are sometimes curved, in keeping with the shape of the zone. When confluent necrosis is more extensive, involving zones 2 and 1 in addition to zone 3, such that entire acini are destroyed, the process is described as ‘panacinar’ or ‘panlobular’ necrosis.
Interface hepatitis, formerly known as ‘piecemeal necrosis’, can be defined as death of hepatocytes at the interface of parenchyma and the connective tissue of the portal zone, accompanied by a variable degree of inflammation and fibrosis. Interface hepatitis was a defining feature of the formerly used category of ‘chronic active hepatitis’, but similar periportal inflammation and hepatocyte death are found in some cases of acute hepatitis.
Light microscopy appearance: patterns of acute viral hepatitis
Classic acute hepatitis
Features seen in the parenchyma in the classic form of acute hepatitis include liver cell damage and cell death, liver cell regeneration, cholestasis, infiltration with inflammatory cells and prominence of sinusoidal cells ( Fig. 6.2 ). The necrosis may be spotty or confluent. The histological changes, especially confluent necrosis, are often most severe near the terminal hepatic venule. The reason for this zonal distribution has not been established, but possible explanations include metabolic and functional differences among hepatocytes in different zones and the lower oxygen content of the blood in perivenular areas. There is a variable degree of condensation of the reticulin framework, but in the classic form of hepatitis, this does not amount to substantial alteration of structure and vascular relationships. Portal tracts are inflamed, and bile ducts may be damaged.
Little is known about the earliest changes of acute viral hepatitis in humans. Available information suggests that Kupffer cells are prominent and may show mitotic activity, and that hepatocellular necrosis occurs early in the disease course. In the setting of acquired hepatitis after LT, hepatocyte necrosis is seen as an early indicator of hepatitis.
Hepatocyte swelling is a common feature in acute hepatitis and results mainly from dilation of the endoplasmic reticulum. The swollen cells are pale staining as a result of intracellular oedema ( Fig. 6.3 ). Because of their combined swelling and rounding, these cells appear similar to the ‘ballooning degeneration’ seen in alcoholic and nonalcoholic fatty liver disease, but they should not be mistaken as indicative of such concomitant injuries. The nuclei of the affected cells are also swollen, because of the accumulation of proteins. Nucleoli of hepatocytes may be more prominent than usual, mitotic figures are occasionally seen, and multinucleation may be increased.
In addition to swollen cells, there are hepatocytes undergoing apoptosis with deeply acidophilic cytoplasm, in which the nucleus may be seen undergoing pyknosis. Such acidophilic hepatocytes are small compared with ballooned cells but may occasionally be larger than normal hepatocytes. Acidophilic cells have round or irregular outlines, sometimes assuming rhomboid, angular shapes, apparently determined by the pressure from adjacent swollen hepatocytes. Acidophil bodies—rounded, apoptotic cell remnants extruded from the hepatocyte plates and now located in the sinusoids ( Fig. 6.4 )—are probably a later stage of this process. These may or may not contain pyknotic nuclear remnants and may appear thick and refractile. Affected cells eventually undergo fragmentation and phagocytosis by macrophages. Some acidophil bodies are in close contact with lymphocytes or Kupffer cells, whereas others appear to lie free within liver cell plates or sinusoids, with no other cells in proximity. As with ballooned hepatocytes, acidophil bodies are not specific for acute viral hepatitis, although they often constitute a striking histological feature of the disease.
Loss of individual hepatocytes leads to localized defects in the liver cell plates, with consequent distortion and condensation of the supporting reticulin framework, especially when the cell death is confluent. Although an overall increase in connective tissue is probably slight in acute hepatitis and therefore difficult to detect by light microscopy (with conventional staining methods), immunocytochemical and ultrastructural evidence indicates synthesis of collagen fibres and associated proteins such as fibronectin, as well as increased prominence of stellate cells. There may also be degradation of these components, so that presumably a dynamic balance determines the degree of fibrosis in an individual case. The distortion of cell plates is accentuated by regeneration of hepatocytes. This is recognized by the appearance of mitotic figures, rare in normal liver, and by a change in the structure of the cell plates; these become more than one cell thick or assume the structure of short cylinders known as liver cell ‘rosettes’. The end result of focal necrosis, reticulin condensation and regeneration is a diagnostically helpful disarray of the liver cell plates (see Fig. 6.3 ).
Cholestasis is common in acute hepatitis. It varies from the presence of scanty, small bile plugs in perivenular canaliculi to extensive bile plug formation with canalicular dilation. Intracellular bile is more difficult to recognize because bile is easily confused with lipofuscin pigment. For this reason, cholestasis should only rarely be diagnosed on the basis of routine stains in the absence of canalicular bile plugs. Morphological cholestasis may be accompanied by clinical and biochemical features of cholestasis, but this is variable.
The inflammatory infiltrate of acute viral hepatitis is mainly composed of lymphocytes, plasma cells and macrophages in varying proportions (see Figs 6.2 and 6.4 ). Within the parenchyma, the infiltrate is most abundant where liver cell damage is greatest, usually in the perivenular zones. Lymphocytes are often attached to endothelial cells of the central and portal venules. Mononuclear phagocytes, either activated Kupffer cells or circulating phagocytes, are seen as large, irregular cells in areas of liver cell dropout ( Fig. 6.5 ). They often show brown pigmentation from phagocytosis of bile or accumulation of lipochrome pigment. Iron is also abundant in some cases. The iron-containing phagocytes are sometimes found in the form of small clumps composed of several cells. Whatever the pigment, the periodic acid-Schiff (PAS) reaction after diastase digestion is usually strongly positive ( Fig. 6.5 ).
Most portal tracts in acute viral hepatitis are infiltrated with inflammatory cells to a greater or lesser extent, and in the classic form, lymphoid cells predominate. Cytotoxic T cells (CD45RO+) typically are more prominent than B cells (CD20+). Plasma cells are common, the majority containing IgG. Perls-positive, iron-rich macrophages may be present. Portal infiltration may be diffuse or focal. Mild bile duct damage is common and is seen as minor irregularities of shape, size and arrangement of the epithelial nuclei of the small, interlobular ducts. Less frequently, the ductal epithelium becomes vacuolated and disrupted; such lesions are seen most often near or within lymphoid follicles, but granulomas are not associated with the duct lesion as in primary biliary cholangitis. Irregular dilation of ductules is not typical but has been described in hepatitis A. In general, however, a finding of dilated, bile-containing ductules or canals of Hering, referred to as ‘ductular cholestasis’ or ‘cholangitis lenta’, should arouse a suspicion of sepsis, a complication of severe acute hepatitis in some patients. Bile duct damage in acute hepatitis does not usually correlate with a prolonged cholestatic clinical course, probably because there is not the widespread and progressive destruction of the duct system found in disorders such as primary biliary cholangitis.
The outlines of the portal tracts may remain intact and sharply delineated in classic acute hepatitis with spotty necrosis. More often, infiltration by lymphoid cells and accompanying disruption of the limiting plate of hepatocytes lead to an irregular outline (or interface hepatitis). Severe periportal necrosis and inflammation in acute hepatitis is discussed later.
All the previous features of classic acute hepatitis with spotty (focal) necrosis vary in extent. Therefore the appearance ranges from a mild hepatitis with minimal cell damage or inflammatory cell infiltration to widespread changes throughout the parenchyma. In the latter case the diagnosis is largely straightforward, but in the former the distinction from nonspecific reactive changes or nonhepatitic cholestasis may be difficult or even impossible. These characteristics of classic acute hepatitis with spotty (focal) necrosis also form the basis of the other three forms of acute hepatitis, which may be regarded as exaggerations of one or another component of the classic form.
Variants of classic acute viral hepatitis
Multinucleation may be prominent with the formation of giant hepatocytes ( Fig. 6.6 ). When this change is widespread, the appearances resemble those of neonatal giant cell hepatitis. In addition, cholestatic variants have been described, especially in association with hepatitis A and E. In these cases the degree of necrosis may be minimal and the cholestasis quite prominent, mimicking biliary obstruction.
Acute hepatitis with confluent (bridging) necrosis
In the confluent form of acute hepatitis, the features described for classic acute hepatitis with spotty (focal) necrosis are seen, but in addition, bridging in the form of confluent necrosis linking central venules to portal tracts (central-portal bridging) or linking central venules to each other (central-central bridging) may also be present.
Of these two forms of confluent necrosis, central-portal bridging may be more significant for the progression of the lesion than the central-central necrosis. For example, in patients who develop chronic liver disease, central-portal confluent necrosis may hasten the onset of cirrhosis by creating early disruption of the normal architectural relationships on conversion of the bridges into fibrous septa, which undergo contraction. In patients who do not develop chronic hepatitis, bridging necrosis of central-to-portal type may lead to a certain degree of scarring and distortion, sometimes seen in biopsy specimens taken many months after the acute attack. However, the prognostic significance of central-portal bridging necrosis remains controversial. Boyer and Klatskin believed that patients with this type of bridging necrosis were more likely to develop chronic hepatitis, a conclusion later supported by another study. However, both these groups included not only central-portal bridging as previously described, but also bridges linking portal tracts, probably representing periportal necrosis. Others do not consider bridging as a good predictor of chronicity. Nevertheless, bridging must be regarded as an important histological feature seen in the more severe forms of acute hepatitis.
The appearance of the necrosis varies according to the stage of the illness. In the early stages of bridge formation, substantial numbers of hepatocytes die. This is followed by disappearance of the affected cells, leaving a loose connective tissue stroma infiltrated with lymphocytes and macrophages ( Fig. 6.7 ). With time, the stroma collapses to form more or less dense ‘passive’ septa, which intersect the liver tissue. Confluent/bridging necrosis can develop in the early weeks of acute hepatitis, but its absence on a biopsy sample does not exclude the possibility that it will develop later.
The combination of necrosis, collapse and hepatocellular regeneration leads to architectural distortion that in turn can easily be mistaken for that of chronic hepatitis or cirrhosis when examining only haematoxylin and eosin (H&E)-stained slides. Helpful differentiating features include the presence of other lesions of acute viral hepatitis and the staining properties of the septa. In addition, the stroma in zones of recent necrosis will tend to show the residual structure of the cell plates on reticulin stain ( Fig. 6.8 ); this is not readily seen in chronic hepatitis or cirrhosis. The stroma is often more haemorrhagic or contains more macrophages than in typical chronic hepatitis. Trichrome stains may also show a two-tone appearance, with darker staining of established areas of scar due to thicker collagen bundles (comparable to the normal residual portal tract collagen), compared to lighter staining of areas of recent collapse, where the residual framework and lack of hepatocytes account for the staining ( Fig. 6.9 ). Also, recently formed passive septa are virtually devoid of elastic fibres ( Fig. 6.10 ), whereas the older septa of chronic hepatitis and cirrhosis contain increasing numbers of these fibres. Extensive liver cell destruction in acute hepatitis with confluent necrosis will also display significant ductular reaction at the interface of portal tracts and parenchyma, aspects of which are also often contained within the areas of bridging necrosis themselves; these are absent in the fibrous septa of chronic hepatitis.
Acute hepatitis with panlobular (panacinar) necrosis
The panlobular form of acute hepatitis represents the most severe degree of necrosis, with complete or near-complete destruction of hepatocytes in entire lobules. When several adjacent lobules undergo necrosis, the term ‘multilobular’ or ‘multiacinar’ is applicable. The term ‘massive hepatic necrosis’ has been used when the liver shows extensive, diffuse panlobular (panacinar) and multilobular necrosis >60–70%, as noted on examination of the entire liver on explant, autopsy or clinical visualization. This lesion is typically the morphological counterpart of the clinical condition of acute liver failure (see Table 6.2 ), or fulminant liver failure, which is often fatal. The term ‘submassive necrosis’ has also been sometimes used for lesions that involve global necrosis of 30–70% of the entire liver.
For reasons as yet unknown, panlobular necrosis may spare large areas of the liver (see Fig. 6.1 ), although the more viable zones usually show lesser degrees of damage, including bridging necrosis. Thus, determination of the degree of total loss of liver parenchyma based on needle biopsy alone is not recommended because of the topographical variability of the necrosis that can occur in acute viral hepatitis. Panlobular necrosis on a smaller scale is not necessarily accompanied by severe disease clinically and may be seen particularly in a subcapsular location (or rarely at other sites), adjacent to less severely damaged liver tissue. It is even likely that panlobular necrosis can occur in the entire absence of severe symptoms, because areas of past necrosis and collapse may be found incidentally in the liver of patients with no history of acute hepatitis. Conversely, some patients have severe clinical hepatitis in the absence of panlobular necrosis, and it must then be assumed that a large proportion of hepatocytes have sustained sublethal damage.
The macroscopic appearance in this form of acute hepatitis is described earlier. Microscopically, acute hepatitis with panlobular necrosis is characterized by extensive liver cell loss, the presence of ductular-like structures around portal tracts, inflammatory cell infiltration and collapse ( Figs 6.11 and 6.12 ). The degree of collapse may be judged by the extent of approximation of adjacent portal tracts, which increases over time, and by the density of the collapsed reticulin framework. As in confluent/bridging necrosis, areas of recent collapse contain few if any elastic fibres, whereas staining for these fibres becomes positive later. Haemorrhage in the collapsing zone may be prominent in some cases (see Fig. 6.11 ). Inflammatory cell infiltration is mixed and variable in degree. The main infiltrating cells are often macrophages (see Fig. 6.12 ), which usually contain lipochrome pigment and should not be mistaken for residual hepatocytes. Mononuclear infiltrates in areas of surviving parenchyma are sometimes surprisingly mild compared with classic acute hepatitis. Ductular reactions contain cells with morphology ranging from hepatocytic to cholangiocytic, with many intermediate forms; some suggest these features represent a role for hepatobiliary stem cell response, although biliary metaplasia of injured hepatocytes may also play a role. Venulitis of central veins can be seen ( Fig. 6.13 ). Evidence of significant parenchymal cell regeneration is present even in fatal cases.
The common hepatotropic viruses can cause panlobular necrosis, but the mechanisms responsible for development of massive necrosis, instead of the more typical pattern of spotty necrosis, are unknown. Possibilities include overwhelming viral infection, superinfection with a second virus and microcirculatory failure. In some cases, mutants of the hepatitis B virus have been implicated.
Acute hepatitis with periportal necrosis
In this pattern the usual changes of classic acute hepatitis are seen to a greater or lesser extent, but there is also a substantial degree of necrosis in the periportal zones, accompanied by significant periportal inflammatory infiltration ( Fig. 6.14 ). Lymphocytes and plasma cells usually predominate in the portal and periportal infiltrate. Ductular reaction may be present. One effect of the periportal necrosis is apparent widening of the portal tracts and linking of tracts, as seen in two-dimensional sections. Changes in other parts of the parenchyma may be mild or severe. In some patients with hepatitis A, for example, the portal and periportal changes may be accompanied by minimal perivenular necrosis. In contrast, with other patients the biopsy may show a combination of periportal necrosis and central-portal bridging.
Unlike the periportal necrosis (interface hepatitis) of chronic hepatitis, trapped periportal hepatocytes are usually absent or scant in number in the necrotic zone of acute hepatitis. Nevertheless, a close resemblance is seen between these two types of necrosis. Patients with acute hepatitis may thus be incorrectly diagnosed with chronic hepatitis on biopsy. This error can usually be avoided if the patient’s history is unequivocal and available to the pathologist, and if an examination is performed for the typical parenchymal changes of acute hepatitis.
Evolution of the lesion
As previously noted, little is known about the early stages of acute hepatitis. The descriptions given in this chapter refer to the fully developed acute lesion, but the time over which this lesion develops varies widely from patient to patient. In some the lesion begins to regress after a few weeks, whereas in others the course is over many months. There is international agreement that the term ‘chronic hepatitis’ should be used for inflammation of the liver continuing without improvement for more than 6 months. However, there is overlap between acute and chronic disease; acute hepatitis may last for more than 6 months in some patients, regressing slowly thereafter, whereas chronic hepatitis may become established in the first few weeks or months.
Following the fully developed stage of acute hepatitis, there is a stage of regressing and finally residual hepatitis. During regression, necrosis diminishes or ceases and phagocytic activity predominates. Portal inflammation is still seen, and in severe hepatitis, there may be ductular reaction. In patients with marked cholestasis, bile stasis can persist after much of the inflammatory activity and necrosis has subsided, often in association with a cholestatic clinical course. Condensation of the reticulin framework marks zones of liver cell loss, and necrotic bridges undergo collapse to form passive septa. The risk of confusion with chronic liver disease and/or cirrhosis thus increases. In this regressing stage, however, the lesion can still be recognized as acute hepatitis on the basis of hepatocellular changes, parenchymal inflammation and phagocytic activity. In severe forms of acute hepatitis with collapsing stroma, the absence of established scarring, as evidenced by lack of dense bundles of collagen and elastic fibres, can help distinguish acute from chronic disease.
The stage of regression passes imperceptibly into a residual stage, which is much less characteristic and easily mistaken for a nonspecific reaction unrelated to viral hepatitis. Changes include slight alterations of architecture, minor degrees of septum formation, focal liver cell regeneration (as shown by variation in liver cell size and appearance from one area to another), inflammatory infiltration and Kupffer cell activation. Clumps of Kupffer cells containing iron or lipochrome pigment are often present. Cholestasis, if still present, is mild. Gradually, these residual changes fade, and the liver returns to normal. Minor degrees of inflammation and phagocytic activity may be seen up to 1 year or more after onset.
Differential diagnosis of acute hepatitis
Acute viral hepatitis is only one cause of an acute hepatitis syndrome, and the typical clinical question on presentation is the aetiology of new-onset hepatic injury. This challenge is generally a clinical question rather than a pathological differential, because diagnostic liver biopsy is usually not pursued in the acute setting. If a biopsy is done, the lesions of acute hepatitis are sufficiently diffuse within the liver to be diagnosed with confidence on small specimens. This may not hold true for some examples of panlobular necrosis, but this exception rarely presents real diagnostic problems when clinical data are taken into account. It should be noted, however, that it is difficult to distinguish a cause for acute hepatitis by morphological means alone, so clinical information and correlation are imperative.
The most common causes of an acute hepatitis syndrome include hepatotropic viral infection, drug toxicity, toxin or alcohol exposure and hepatic hypoperfusion. Other aetiologies may present as an acute hepatitis syndrome, but may be the presenting feature of a chronic underlying disorder such as autoimmune hepatitis, hepatic lymphoma or Wilson disease.
In general, acute viral hepatitis should be considered in any presentation of acute hepatitis and appropriate history obtained to assess possible exposure to each of the hepatotropic viruses. The aetiology of acute viral hepatitis is appropriately evaluated by assessing the presence of antibody to the respective viral types. Acute hepatitis A virus (HAV) infection is indicated by the presence of IgM anti-HAV antibody. Acute hepatitis B virus (HBV) infection is identified by the presence of hepatitis B surface antigen (HBsAg) with coexisting IgM anti-hepatitis B core antibody (IgM anti-HBc). Acute hepatitis C virus (HCV) infection is defined earliest by the presence of HCV RNA, although current assays for hepatitis C antibody (anti-HCV) are sensitive and able to detect anti-HCV after several weeks of infection. Diagnosis of hepatitis D virus (HDV) is hampered by the limited availability of standardized and approved testing. Acute infection with HDV is defined by the presence of HDV RNA in serum and antibody testing showing anti-HDV IgM. Although antibody may be both IgG and IgM, the IgM response usually predominates in acute infection. Anti-HDV IgM levels fall if acute infection resolves. HDV always exists in the context of hepatitis B co-infection because HDV requires the metabolic capability of HBV to survive. The testing for hepatitis E virus (HEV) is limited by the variable performance of serologic tests. HEV infection can be detected by the presence of an antibody to the virus (IgM anti-HEV) and detection of HEV RNA. The pretest probability of HEV infection impacts the interpretation of test results, and a significant proportion of ‘positive’ tests for anti-HEV done in areas of low prevalence may be false positive.
Other viral infections, such as Epstein–Barr virus (EBV) or cytomegalovirus (CMV), may also be responsible for acute liver injury. Histological clues may suggest these viral infections. In infectious mononucleosis (EBV related), for example, liver cell damage is usually absent or mild, and atypical lymphocytes are seen in sinusoids and portal tracts. In the other herpes-type viral infections (e.g. herpes simplex, CMV), the necrosis is often confluent rather than the single-cell spotty type, and a minimal associated lymphoid infiltrate is present in the sinusoids. The typical viral inclusions can often be seen. The histological findings of these viral infections are discussed in Chapter 7 . Other infectious agents, including syphilis, dengue fever and yellow fever, may be considered as the clinical history suggests.
Acute cholestatic hepatitis may be induced by hepatotropic viral infection but must be distinguished from acute, large-bile duct obstruction, which can present with prominent transaminase elevation during the first days of presentation. This pattern is generally followed by a rise in ALP and bilirubin values, especially when obstruction is high grade and unremitting. The presentation is usually accompanied by right upper quadrant or abdominal pain but may be occult, particularly in diabetic or elderly patients. Biliary imaging studies, such as ultrasound or magnetic resonance cholangiography, are sensitive in defining this pathology, particularly if the biliary obstruction is associated with jaundice.
Other relatively common cholestatic hepatitis syndromes include drug/toxin-induced liver injury and alcoholic hepatitis. Less frequently, this syndrome may be simulated by cholestasis of pregnancy, benign recurrent cholestasis or the exacerbation of a chronic underlying cholestatic disorder, such as primary sclerosing cholangitis or primary biliary cirrhosis. The bile duct lesion of acute hepatitis can usually be distinguished from that of biliary tract diseases (e.g. primary biliary cirrhosis) by the presence of the parenchymal features of acute hepatitis, lack of granulomatous duct lesions, ductopenia and other clinical and biochemical findings. Granulomas associated with bile duct lesions are almost never seen in acute hepatitis. The presence of lobular changes also helps distinguish hepatitis from primary biliary cirrhosis. However, sinusoidal lymphocytic infiltrates are relatively common, and even spotty necrosis is seen in primary biliary cirrhosis, so clinical correlation is always advised if the histological changes are equivocal. In addition, bile ductular reaction tends to be less prominent in hepatitis (except in more severe forms of hepatitis), and the periportal hepatocytes do not retain copper, as in the chronic cholestatic diseases. Overall, the key features for distinguishing these two entities may lie in the examination for granulomatous duct lesions or loss of the interlobular bile ducts in primary biliary cirrhosis.
In cholestasis from any cause, secondary changes in hepatocytes and accompanying inflammation may cause confusion with acute hepatitis. In cholestasis the changes are generally confined to the cholestatic areas, and liver cell plates show little or no disruption, although some regenerative changes can be present. Spotty hepatocellular necrosis can be a key histological feature to differentiate a cholestatic hepatitis such as hepatitis A from bile duct obstruction. Furthermore, bile retention is almost never seen in early stages of primary biliary cirrhosis, so in the absence of ductopenia, the presence of canalicular cholestasis would favour a hepatitis or obstruction. Portal changes vary according to the cause of the cholestasis and may also help to establish a correct diagnosis, but both hepatitis and biliary diseases may show varying degrees of portal mononuclear infiltrates and interface hepatitis.
Drugs and toxic agents should always be suspected as a possible cause of acute hepatitis syndrome (see Chapter 12 ). Correlation of the temporal relationship of liver disease to administration of the drug is essential in any type of possible drug reaction, either idiosyncratic or toxic. Hepatic injury is generally recognized at least 5 days after initiating drug exposure but may become evident during the first year of administration or later. The pattern of liver test abnormalities may be hepatocellular with prominent transaminase elevation, although some agents such as chlorpromazine generate a predominant cholestatic pattern of liver test results. Mixed patterns are also possible. Drugs, environmental toxins, ‘health’ supplements, vitamin preparations and over-the-counter (OTC) therapies all need to be considered as possible causes when evaluating acute hepatic injury. Most recently, the growing use of alternative medicine has focused attention on the potential hepatotoxicity of ‘natural’ products or herbal agents. Although systemic evidence of hypersensitivity, such as rash or eosinophilia, may support drug hepatotoxicity, these findings are not necessary for the diagnosis. Histopathological findings may include injury of varying severity, from bridging necrosis to massive necrosis. Features that should raise a greater degree of suspicion for an idiosyncratic type of drug hepatitis include a poorly developed or absent portal inflammatory reaction, abundant neutrophils or eosinophils, granuloma formation, sharply defined perivenular necrosis with little inflammation or a mixed pattern of hepatitic and cholestatic features with duct damage; the latter may be a prominent feature. Direct toxic reactions such as paracetamol (acetaminophen) toxicity typically have a uniform pattern of perivenular necrosis with a minimal inflammatory component.
Acute alcoholic hepatitis is usually an exacerbation of a chronic condition. The degree of elevated transaminase values is generally modest and does not reflect the severity of injury. Typically, aspartate transaminase (AST) levels are greater than alanine transaminase (ALT) values, and prominent elevation of γ-glutamyltransferase (GGT) is typical. GGT activity is a reflection of enzyme induction rather than the severity of hepatotoxicity. ALP and bilirubin values typically rise as transaminase values improve following abstinence.
In alcoholic hepatitis, ballooning of hepatocytes is usually seen in perivenular (central) zones, often accompanied by a predominantly neutrophilic infiltrate with or without new collagen fibres around affected hepatocytes; fatty change and Mallory–Denk bodies (MDBs) are often present (see Chapter 5 ). In contrast, nonalcoholic steatohepatitis (NASH; see Chapter 5 ) may have a more intense lymphocytic infiltrate and absent or less prominent MDBs. This entity is not typically in the clinical differential diagnosis, however, because of the lack of jaundice and the milder, more chronic nature of the transaminase abnormalities.
Autoimmune hepatitis can present as an acute hepatitis syndrome as well (see Chapter 8 ), with transaminase values more than five times the upper limit of normal. When this occurs, histological changes are similar to those of acute viral hepatitis with extensive hepatocyte necrosis and inflammatory infiltrates, especially in the perivenular (central) zone. Plasma cells are likely to be prominent in autoimmune hepatitis, but they may be variable in number in viral hepatitis and may be a common component of the inflammatory infiltrate in acute hepatitis A, so the presence or absence of these cells cannot be used as a definitive distinguishing feature. Serum markers for autoimmune antibodies as well as elevated γ-globulin levels >2 g/dL are typically present to distinguish these lesions.
Wilson disease can also rarely present as acute liver failure, and the histology can be similar to acute viral hepatitis (see Chapter 3 ). However, some of these patients may have underlying evidence of chronic injury, such as established scarring, demonstrated by densely staining collagen bands in the form of septa and increased elastic fibre deposition in septa. Tissue from Wilson disease patients may also show copper deposits on histochemical stains, but quantitative copper studies on liver tissue, serum caeruloplasmin or 24-hour urinary copper studies are typically of more value in establishing the diagnosis.
Additional causes of acute liver injury are pursued according to evidence supplied in the medical history. Liver pathology evaluation may be of value in focusing on unanticipated results and assessing the severity of injury. There may be no known cause for the hepatitis in as many as 20% of patients with acute liver failure. The histology of these cases is often similar to the types of changes described in this chapter for severe hepatitis with panlobular necrosis.
Lastly, areas of collapse in acute hepatitis must be distinguished from the fibrous septa of chronic liver disease, as previously discussed.
Sequelae of acute hepatitis
Table 6.3 lists the morphological consequences of acute viral hepatitis. Restitution to normal liver occurs in the classic forms of acute viral hepatitis, and the results of fulminant hepatitis are described earlier under acute hepatitis with panlobular necrosis. The spectrum of lesions of chronic hepatitis is discussed later in this chapter. A viral carrier state without significant histological changes (other than ground-glass hepatocytes in HBV carriers) may possibly develop in hepatitis B as a temporary state.
It is likely that cirrhosis may develop after acute hepatitis because of ongoing hepatitic changes or chronic hepatitis. The idea that cirrhosis can develop directly from massive hepatic necrosis, without the intervention of chronic hepatitis, is expressed in the old term ‘postnecrotic cirrhosis’. Karvountzis et al. followed 22 patients surviving acute hepatitis with coma and concluded that such patients rarely if ever developed chronic hepatitis. On the other hand, Horney and Galambos reported that chronic hepatitis had developed in three of nine patients on follow-up biopsies 6–60 months after fulminant hepatitis. Certainly, nodular regeneration of surviving parenchyma is seen in patients dying weeks or months after the acute attack, but this should not be considered ‘cirrhosis’ because the septa are formed by collapse of pre-existing fibres rather than by true, new collagen deposition (fibrosis); in addition, the nodularity is not usually uniform or diffuse. In a small number of patients who recover from the acute attack, there may be sufficient nodularity, portal-systemic shunting, fibrosis and portal hypertension to warrant a diagnosis of ‘inactive cirrhosis’ even in the absence of chronic hepatitis, but this is probably the exception rather than the rule.
A role for vascular occlusion in the pathogenesis of chronic liver disease and cirrhosis has been proposed, and similar lesions may play a role in postnecrotic scarring following acute hepatitis. The mechanism for the injury would probably start with phlebitis of the hepatic venules (see Fig. 6.13 ) or portal veins, with resultant vascular sclerosis. Occlusion of these veins, in turn, would lead to ischaemia or outflow obstruction in these areas, a process which would impair regeneration and enhance the formation of scar tissue in those zones with severe hepatocyte necrosis and dropout.
Hepatocellular carcinoma (HCC) is a long-term complication of hepatitis B and C. HCC is usually (but not always) seen in end-stage disease associated with cirrhosis and is generally not considered to be a direct sequelae of acute viral hepatitis (see Chapter 13 ).
Chronic viral hepatitis
Chronic viral hepatitis is a syndrome of persisting hepatotropic viral infection usually associated with chronic inflammation, hepatocyte injury and progressive fibrosis. By convention, infection for more than 6 months is considered evidence that spontaneous resolution of infection is unlikely and hepatitis is chronic. A clinical diagnosis of chronic viral hepatitis may be made on an initial clinical evaluation when clinical history or pathological findings suggest chronic infection even in the absence of earlier laboratory data. Chronic viral hepatitis is typically classified by the responsible infecting virus and modified by the extent of pathological injury and clinical compensation. Hepatotropic viruses responsible for this syndrome include hepatitis B, C, D and E. The injury from hepatitis A and E viruses may be severe and relapsing but usually represents acute injury rather than chronic hepatitis. Cases of chronic hepatitis E, however, have been reported in immunosuppressed patients, particularly after LT but also after chemotherapy.
The epidemiology of the various forms of viral hepatitis share modes of transmission, and thus a small but significant number of individuals may have chronic co-infection with multiple viruses. In addition to hepatotropic viruses, human immunodeficiency virus (HIV) also shares epidemiological features with the hepatitis viruses. Individuals with HIV co-infection may experience accelerated injury and progression of liver disease, particularly in the setting of impaired immune function. Progression of fibrosis in the patient with HIV co-infection receiving effective antiretroviral therapy may be similar to that in mono-infected patients (see Chapter 8 ).
The hepatotropic viruses form a group of diverse agents that utilize liver tissue as a site of replication and major pathological injury. The liver is the most common and predominant focus of injury, but the course of disease may vary considerably from person to person. Many patients are asymptomatic, and most are anicteric. Infection with hepatitis B or C may be discovered through screening, which is most fruitful in populations at high risk of exposure. Two-thirds of persons infected with HCV were born between 1945 and 1965. Recognizing this epidemiology, all persons born within this cohort in the United States are recommended to be tested for HCV ( Table 6.4 ). Symptoms of chronic hepatitis may be nonspecific, with fatigue being the most common. Patients may have mild discomfort in the right upper quadrant, pruritus, joint pain or anorexia. As liver disease progresses, muscle atrophy, jaundice, fluid retention and loss of mental acuity may develop.
|Populations at risk for exposure to hepatitis B|
|Populations at risk for exposure to hepatitis C|
The characteristic biochemical abnormality associated with chronic viral hepatitis is an elevation of ALT/AST levels. Typically, transaminase activities range from normal to <10 times the upper limit of normal. On occasion, patients may have flares of hepatitic activity, with enzyme levels >20 times the upper limit of normal. In patients with hepatitis C, this wide range of transaminase values is more often seen early in infection. In patients with hepatitis B infection, increased transaminase levels may be associated with seroconversion of HBe antigen positive to HBe antibody reactivity or new HDV superinfection.
In many patients with chronic viral hepatitis, ALT/AST values are normal. Although the correlation between transaminase values and the degree of liver injury is not precise, in general, asymptomatic individuals with consistently normal transaminase values have a more favourable prognosis than those with elevated levels. However, patients can have significant pathological abnormality, even cirrhosis, despite normal ALT values. In one study, 16% of patients with consistently normal ALT values had significant necroinflammation or fibrosis. Disease progression has been demonstrated in patients with hepatitis C and consistently normal transaminase values.
Hepatic synthetic dysfunction is demonstrated, as chronic hepatitis progresses, by a fall in serum albumin and rise of INR and serum bilirubin. The presence of cirrhosis may be suspected with signs of portal hypertension such as splenomegaly, and laboratory results may show a decrease in platelet count. The AST/platelet ratio correlates with the presence of cirrhosis.
Once a patient is defined as having chronic viral hepatitis caused by a specific hepatotropic virus, it is important to assess the severity of illness and the presence or absence of complications, such as portal hypertension or HCC. Liver biopsy, although imperfect, is useful in this assessment and is the most secure assessment of the stage of disease. Transient elastography, liver imaging and serological methods of assessing the severity of hepatic fibrosis have been extensively studied and are increasingly used to assess for cirrhosis.
These noninvasive methods lack the ability to define the pattern of fibrosis or coexisting pathology. Because of their noninvasive nature and limited expense, these modalities are increasingly used to assess fibrosis, particularly in patients with chronic hepatitis C. Transient elastography measures hepatic fibrosis in patients with chronic hepatitis C with precision approaching liver biopsy; accuracy is highest in identifying patients with advanced stages of fibrosis.
Chronic viral hepatitis is characterized by a combination of inflammatory cell infiltration, hepatocyte death, atrophy and regeneration, and fibrosis. These components, while all present in acute viral hepatitis to some degree, have a different relative proportion and distribution in chronic viral infection. The proportion and distribution may also differ between one viral infection and another, as well as in the same patient with the same infection, over time.
Patterns of inflammation and scarring are discussed here first, followed by the types of scarring that may be seen, if and when the disease progresses. The possible mechanisms of injury and repair responsible for these gross and light microscopy changes are then summarized. Finally, practical issues are discussed regarding routine biopsy specimen assessment in chronic viral hepatitis, including grading/staging and recognition of common concomitant diseases.
The macroscopic appearance of livers with chronic viral hepatitis in advance of cirrhosis has not been systematically described. However, anecdotal observations of such livers obtained at autopsy or in partial hepatectomy for tumours indicate that livers may appear normal, may have focal areas of fibrosis, with a somewhat gritty texture, or may have a diffuse or focally lobulated appearance indicative of fibrous septa and local regeneration ( Fig. 6.15 ). The colour of the liver at these early stages is generally the normal, beefy red because these patients are rarely cholestatic. Some yellow colouring will indicate steatosis.
As cirrhosis develops, there is increasingly diffuse nodularity and obvious fibrous scarring. Classically, cirrhosis associated with chronic viral hepatitis appears either macronodular or mixed micro- and macronodular, although purely micronodular cirrhosis may be seen ( Fig. 6.15 ). A predominantly macronodular cirrhosis seems to be the pattern most often present in patients younger than 40, whereas strictly micronodular cirrhosis in chronic hepatitis should raise the question of concomitant alcoholic liver disease. Nodules may vary in colour, ranging from beefy red to dark green of cholestasis to yellow of fatty change. Some nodules may appear necrotic because of compromised blood supply. Larger portal vein branches may be thrombosed.
Light microscopy appearance: patterns of necrosis, inflammation and fibrosis
Hepatocyte injury and inflammation in chronic hepatitis is referred to as ‘activity’, which is ‘graded’ (see later). Distribution of inflammatory cells may vary from case to case or even in sequential biopsies from the same patient. However, all cases of chronic viral hepatitis are distinguished by a relatively dense mononuclear infiltration of the portal tracts.
Mononuclear infiltration of portal tracts is the defining lesion of chronic hepatitis of any cause. Some or all portal tracts may be involved, and the portal infiltrates are usually much denser than those seen in acute viral hepatitis. The portal tracts may be of normal size or may appear widened by the influx of mononuclear cells. The infiltrate includes predominantly CD4+ helper/inducer T lymphocytes with an admixture of plasma cells; γδ T cells do not appear to be increased beyond their normally low levels. Some portal macrophages may also be seen to contain periodic acid-Schiff (PAS)-positive, diastase-resistant material and iron pigment, representing the removal of hepatocyte debris.
Portal inflammation will often fill and expand the portal fibrous stroma, pushing structures aside without obvious injury. Lymphoid aggregates or fully formed follicles may be seen; while most common in hepatitis C, they are also seen in other forms of hepatitis. However, inflammation with damage or even destruction of bile ducts may also be seen, particularly in hepatitis C. Inflammation may also encroach on the portal blood vessels, in particular the portal veins ( Fig. 6.16 ). Endotheliitis may be present, and there may be associated fresh or organizing venous thrombosis; such lesions may be particularly evident with trichrome stains.
The region of liver tissue where the hepatic parenchyma comes into contact with the mesenchymal stroma of the intact or scarred portal tract is referred to as the stromal-parenchymal interface. Thus, hepatocyte apoptosis and inflammation of this area are generally referred to as ‘interface hepatitis,’ the currently favoured term. Previously, this classic histological feature of active chronic hepatitis was called ‘piecemeal necrosis,’ referring to the way in which the limiting plate of hepatocytes was eroded in a ‘piecemeal’, i.e. focal, manner ( Fig. 6.17 ).
In regions of interface hepatitis, there is a predominantly mononuclear infiltration, although in these regions, Fas ligand-positive CD8+ suppressor/cytotoxic T cells predominate. Close contact of hepatocytes with these lymphocytes, as well as with macrophages and plasma cells, is seen. ‘Emperipolesis’, the invagination of lymphocytes into hepatocytes, has been described. Although the inflammation interweaving among hepatocytes at the interface is sufficient by itself for describing the lesion as interface hepatitis, apoptotic hepatocytes may also be seen in these areas.
Lobular hepatitis and confluent necrosis
Another form of inflammatory activity in chronic viral hepatitis is found within the hepatic lobule away from the portal areas or septal scars. Such lesions may be referred to as ‘lobular hepatitis’ or ‘spotty necrosis’ ( Fig. 6.18 ). The inflammatory infiltrates in these areas of activity are the same as those seen in interface hepatitis, but their relative importance to the development of scarring and progression in chronic viral hepatitis remains uncertain.
Some foci of lobular hepatitis are relatively devoid of mononuclear cells. In these areas, there may be acidophil bodies, clustered macrophages containing PAS-positive, diastase-resistant material indicating prior cell death, or simply cellular debris and loosely aggregated collagen and reticulin fibres. Such lesions are similar to the lobular damage found in acute viral hepatitis.
If large areas are involved, one may refer to the lesion as ‘confluent necrosis,’ which typically is found around central veins but, if still more severe, may span from there to other central veins or to portal tracts, when the term ‘bridging necrosis’ is used. Such bridging necrosis is considered the most ominous finding in terms of progression toward scarring and cirrhosis. In some cases, when one or more entire lobule has been destroyed, it may be referred to as ‘panlobular collapse’ or ‘multilobular collapse’. In these areas, portal tracts will be in abnormally close proximity, separated only by regions filled with necrotic debris, macrophages, loose or more mature collagen and elastic fibres. A ductular reaction, which is now recognized as activation of an hepatic stem cell compartment, is also present and is considered potentially both a regenerative response to hepatocyte injury and senescence and, paradoxically, an instigator of fibrogenesis ( Fig. 6.19 ).
Confluent necrosis in a patient with known chronic viral hepatitis may indicate specific clinical situations related to the known virus (e.g. in HBV, superinfection with HDV or serologic HBeAg-to-HBeAb conversion; in HCV, acute but self-limited flare), but other concomitant injuries should be considered, including immunosuppression and concomitant autoimmune hepatitis or drug/toxin-mediated injury. Clinical correlation is important to investigate all these possibilities when confluent necrosis is seen.
Fibrosis and hepatocyte regeneration
Although some patients with chronic viral hepatitis do not show fibrous scarring, most will have some disruption. The extent of fibrosis and architectural disruption is referred to as the ‘stage’ of disease and may be assessed by means of semiquantitative scoring systems. In chronic viral hepatitis the scarring will usually start as an extension of the portal stroma and progress through the formation of portal-to-portal and portal-to-central fibrous septa. Fibrous septa linking portal tracts to central hepatic veins may represent scarring in regions of bridging necrosis. Septal fibrosis is an important indicator of prognosis, marking the shift from minimal to clinically significant fibrosis. In clinical terms, identification of significant fibrosis implies a decision to treat the patient in order to prevent the progression to cirrhosis.
Perivenular and pericellular fibrosis may also be seen. The perivenular fibrosis usually develops after collapse and condensation of the reticulin meshwork in an area of confluent necrosis. Such perivenular scars are bland and generally acellular, often lacking extensive accompanying interface hepatitis and linking central veins to neighbouring portal tracts or to other hepatic veins, in which case they probably represent healed bridging/confluent necrosis. As previously described regarding comparisons between acute and chronic viral hepatitis, if these scars persist, mature, densely aggregated forms of collagen will deposit, easily demonstrable with trichrome stain. Elastin fibres will follow, usually beginning between 3 and 6 months and becoming denser afterward. Thus, staining of elastic fibres with orcein or Victoria blue stains is a useful tool for evaluating age of a scar.
Fibrous expansion of the portal tract probably results from a vigorous process of injury and repair. There is as yet little agreement on the use of the terms ‘periportal fibrosis’ and ‘portal fibrosis’. Whichever term is used, it refers to fibrous stroma extending from the portal tract beyond its usual boundaries. This fibrosis is usually conceptualized as following Rappaport’s acinus zone 1 and thus eventually leads to linking of one portal tract to another. These septa usually contain mononuclear inflammatory cells as described earlier and may be associated with interface hepatitis ( Fig. 6.20 ). The fibrosis is usually mature, darkly staining with trichrome stains, and containing abundant type I collagen in addition to type III collagen ( Fig. 6.21 A ) and reticulin fibres ( Fig. 6.21 B ). Again, elastic fibres are easily demonstrated, indicating that the scars are of at least several months’ duration. Immunohistochemical staining for α-smooth muscle actin highlights numerous activated stellate cells in these regions, and these cells are thought to be largely responsible for most of the scarring ( Fig. 6.21 C ), although other mesenchymal cells, including portal myofibroblasts and bone marrow-derived fibroblasts, as well as fibroblasts derived from epithelial to mesenchymal transition, may also contribute.
Regeneration of hepatocytes becomes increasingly evident in parallel with the formation of fibrous septa and advancing stages of disease. The thickening of liver cell plates to two or three cells thick demonstrates this regeneration. H&E or silver stains for reticulin can demonstrate these changes. An incomplete periportal nodular transformation may thus be noted around portal tracts that are becoming fibrotic. However, in the later stages of developing cirrhosis, hepatocyte regeneration greatly diminishes along with an increasingly proliferative ductular reaction at the stromal-parenchymal interface. This reaction is believed to be activation of the intrahepatic facultative stem cell compartment as pre-existing hepatocytes reach replicative senescence in response to the chronic injury.
Regression of fibrosis and cirrhosis
Development of scarring in a chronically diseased liver is actually the result of a balance in favour of matrix deposition in a liver dynamically producing and degrading matrix at all time points. Despite decades of dogma that scar formation was a unidirectional process, regression of fibrosis has now been demonstrated in all forms of chronic liver disease. In particular, a large body of clinical evidence from patients treated for chronic HBV or HCV infection suggests that regression from hepatic fibrosis occurs if the underlying liver injury is resolved or successfully treated. Removal of the etiological agent decreases inflammatory and fibrogenic cytokine levels, increases collagenase activity and promotes the disappearance of activated hepatic stellate cells. Most importantly, the reduction of liver fibrosis has been associated with clinical improvement.
The dogma of the irreversibility of cirrhosis, with cirrhosis generally thought to be the ‘end stage’ of chronic liver disease, has also been challenged over the years. Indeed, the validity of the term ‘cirrhosis’ itself, indicating an end-stage liver disease, has come into question. Regression of cirrhosis is complex, however, since cirrhosis itself is a complex disease, characterized not only by fibrosis deposition but also by severe architectural disarray with important vascular modifications, ultimately leading to development of portal hypertension. Thus, cirrhosis regression implies reabsorption of collagen as well as rebuilding of the normal lobular architecture, which is difficult to demonstrate, particularly in needle biopsy samples that are prone to sampling error. Nevertheless, clinical demonstration of cirrhosis regression has been provided in studies involving large cohorts of patients with chronic hepatitis B and C effectively treated with antiviral drugs. Despite these demonstrations, whether and to what extent cirrhosis may reverse remains a debated issue. In an experimental study, Issa et al. observed that in cirrhotic rodents intoxicated with carbon tetrachloride (CCl 4 ), fibrotic septa failed to regress completely, even 1 year after therapy withdrawal and recovery of the animals, resulting in an attenuated macronodular pattern. A similar ‘remodeling’ of cirrhosis has been described in humans. Wanless et al. examined a series of 51 explanted cirrhotic livers and provided evidence that micronodular cirrhosis may transform into macronodular or incomplete septal cirrhosis, a condition characterized by persistent vascular changes. These findings support the concept that regression of fibrosis (in cirrhosis) and regression of cirrhosis are not equal.
In their study, Wanless et al. described eight histological features thought to reflect parenchymal remodeling related to fibrosis regression. These features were referred to as ‘hepatic repair complex’ and can be grouped into features evincing three regenerative phenomena: fragmentation and regression of scar (e.g. delicate perforated septa [ Fig. 6.21 D ], isolated thick collagen fibres [ Fig. 6.21 E ], delicate periportal fibrous spikes, hepatocytes within or splitting septa [ Fig. 6.21 F ]), evidence of prior now-resolving vascular derangements (e.g. portal tract remnants [ Fig. 6.21 G ], hepatic vein remnants with prolapsed hepatocytes [ Fig. 6. 21 H ], aberrant parenchymal veins [ Fig. 6.21 I ]) and parenchymal regeneration in the form of hepatocyte ‘buds’. These hepatocyte buds are small clusters of hepatocytes, usually emerging from within portal/septal stroma, and represent regeneration from the stem cell niche rather than entrapment of parenchyma by active scarring. The value of assessing changes in the hepatic repair complex in routine clinical practice is not established, although it has been suggested that observing these features may be a more sensitive way to detect fibrosis regression in chronic hepatitis.
General mechanisms of injury and repair apparently are common to all hepatotropic viral infections, with some involving viral determinants and others defined by host response, the complex interplay of which determines the outcome of viral hepatitis. Direct cytotoxicity of the hepatotropic viruses is probably a smaller contributor. Indeed, a large number of virus–host interactions take place in virus-infected cells. For example, viruses are able to usurp host factors to aid in the translation and replication of the viral genome. On the other hand, many viruses may neutralize the host innate immune system by encoding factors that mimic host cell ligands to inhibit host cell signalling or proteinases that degrade factors of the innate immune response. Importantly, the continued testing and development of antiviral drugs and immunomodulators are allowing clinicians increasingly to influence the balance and therefore alter outcomes of these infections.
In acute hepatitis the most appropriate response is when the immune system can outpace the spread of the infection, eliminating viral particles from all infected cells or eliminating the infected cells directly. With efficient regeneration of hepatocytes, either from mature hepatocyte division or from activation of stem/progenitor cell compartments, the liver can recover, re-establishing normal architecture and function. However, if the viral infection is not kept in check by an active immune response, progressive immune destruction of the liver results in acute liver failure.
Studies in animal models and clinical observations provide evidence that viral hepatitis is initiated by an antigen-specific intrahepatic cellular response that sets up a cascade of antigen-nonspecific cellular and molecular effector systems. Both the cellular and the humoral limbs of the immune response act toward viral clearance by different mechanisms. The initial response to viral infection involves the killing of infected cells with cytotoxic T lymphocytes (CTLs) such as natural killer (NK) cells or virus-specific CTLs. NK cells are able to kill immature dendritic cells and secrete proinflammatory cytokines, thus supporting the priming of T cells and orchestrating the recruitment of other immune cells to the site of infection.
Different mechanisms may help viruses to survive. For example, viral gene products may inhibit apoptosis of infected cell populations. From the viral point of view, blocking the apoptotic system is of value to ensure ongoing viral replication, but this may be fatal in terms of carcinogenesis. Host cellular and molecular factors may also impact cell apoptosis. For example, it has been recently demonstrated in a mouse model of chronic HBV infection that cellular inhibitor of apoptosis proteins (cIAPs) attenuate tumour necrosis factor signalling during HBV infection and restrict the death of infected hepatocytes, thus allowing viral persistence. Moreover, mutations of the viruses may lead to escape from both humoral and cell-mediated immune responses. Infection of extrahepatic, immunologically tolerant or privileged sites may encourage viral persistence.
Alternatively, the immune system may be generally or selectively impaired in response to the specific virus. Patients with a generalized immunosuppression, such as those co-infected with HIV or patients receiving immunosuppressive therapy for unrelated diseases, are at increased risk for developing chronic infection after acute exposure to a hepatitis virus. Selective immune system defects may also occur, either pre-existing (perhaps genetically determined) or influenced or induced by viral factors.
Regardless of the specific mechanisms involved, the virus is able to infect hepatocytes beyond the ability of the immune system to kill the infected cells or to induce suppression of the viral replication, thereby maintaining a chronic presence in the liver and provoking, to variable degrees in different individuals, ongoing immune-mediated damage to the liver and its sequelae. In many patients the outcome of this damage is development of scarring, sometimes leading to cirrhosis. Furthermore, the chronically inflamed and infected liver becomes fertile ground for hepatocarcinogenesis, through genetic and epigenetic alterations and oncogenic effects mediated by viral proteins, inactivation of tumour suppressor genes, dysregulation of multiple signal transduction pathways and altered microRNA pathways.
The role of humoral immunity
Virus-specific antibodies play a relatively limited role in the development of viral hepatitis. Specific antiviral antibodies can protect against infection initially; thus vaccine-induced anti-HAV and anti-HBs antibodies can prevent these infections. Humoral immunity against hepatitis C, however, is not protective of infection, although both innate and adaptive humoral responses to HCV infection modify viral infection of hepatocytes and mediate pathogen removal. Humoral responses to the viruses can lead to immune complex diseases such as glomerulonephritis, vasculitis and cryoglobulinaemia.
The role of cellular immunity
As mentioned, cell-mediated immunity, particularly the CTL response, is thought to be central to the elimination of viral infections of the liver (see Chapter 1 ). Functional cytotoxic CD8 T cells are essential for the resolution of acute HBV and HCV infections; after activation they are able to kill infected cells and secrete cytokines with direct antimicrobial properties. Failure to generate a productive antiviral response results in persistent viral replication that promotes chronic liver disease. Factors affecting outcome of activation of CD8 T cells specific for hepatocyte-expressed antigen include the nature of the antigen-presenting cell, physical location of primary activation, the presence or absence of inflammation and the antigen dose.
Activation of CD4+ T-helper (Th) cells throughout the major histocompatibility complex (MHC) class II pathway is also important for viral clearance, whether by stimulating CTL responses, inducing different patterns of cytokine production, or through some direct, Fas-mediated cytotoxic activity. Recruitment and activation of these immune cells have been shown to be partly mediated and promoted by platelet aggregation in the hepatic microcirculatory system, leading to release of platelet-derived substances such as serotonin.
However, the number of potentially infected cells in the liver can far outweigh the available, but proliferating, virus-directed lymphocytes. Thus, although direct cell–cell interactions are probably important, diffusible cytokines produced or induced by these lymphocytes may be a more important factor in viral clearance. CD1d-reactive T cells, variants of NK cells, are seen to play important roles in production of these diverse cytokines as well, mediating through both Th1 and Th2 pathways. In addition, classic FOXP3+ CD4+ regulatory T (Treg) cells, interleukin-10 (IL-10)-producing Treg1 cells, transforming growth factor β (TGFβ)-producing Th3 cells and CD8+ Treg cells all may play important roles.
The role of cytokines
Cytokines are essential in the body’s defense mechanism, either directly by inhibiting viral replication or indirectly by determining the predominant pattern of host immune response, which is regulated by human genetic background and modulates outcomes of chronic viral hepatitis. For example, specific cytokines have proven involvement in anti-HCV-directed adaptive immune responses that determine the maintenance or resolution of viral infection. Furthermore, HCV itself can modulate cytokine expression, thereby helping to escape efficient immune responses.
The interferons have been shown to inhibit multiple viral infective/replicative processes, from entry into the cell to viral gene translation and protein synthesis. Through these activities, viral clearance from infected cells, even in the absence of cell death, can occur, extending the antiviral capabilities beyond the limits of cell-mediated immunity. It is well established that types I, II and III interferons directly inhibit the replication of hepatitis B virus. The importance of interferons for viral control is implied by their long-term clinical utility in treating some patients with hepatitis C. Interferons also induce production of host cell proteins, including HLA class I and II antigens. Macrophages, NK cells and CTLs are also stimulated by interferons.
Tumour necrosis factor (TNF), produced by macrophages and T cells, stimulates chemotaxis, activation of macrophages and induction of class I and II antigens and T-cell activation and modulates acute-phase protein transcription, among other functions. A direct antiviral effect of TNFα in HBV-infected hepatocytes has also been demonstrated. Interleukin-1 (IL-1) is a highly proinflammatory cytokine produced by multiple cell types, including epithelial cells, macrophages, dendritic cells, endothelial cells and B cells. IL-1 may play a role in viral clearance and can protect against HBV infection. IL-1 actions include enhancement of lymphocyte and fibroblast proliferation and activation and induction of acute-phase reactants. IL-6, produced by monocytes, fibroblasts and endothelial cells, induces B-cell differentiation and acute-phase proteins and is a growth factor for T cells. IL-6 has been found to induce a direct anti-HBV effect in replicating hepatocytes.
Cytokines can also be produced during chronic phases of infection, when they are not much involved in the inhibition of viral replication, but instead contribute to immunopathogenesis. Indeed, cytokines have been involved in orchestrating the inflammatory response during disease progression in the liver, influencing the development of fibrosis and cirrhosis. Profibrotic cytokines, including IL-4 and IL-13, may also play a role in fibrosis. Thus these cytokines have overlapping as well as distinct effects. At the same time, all cytokines may not be favourable, with evidence now suggesting a role for IL-10 and TGFβ in supporting chronic viral persistence.
The role of microRNA
Recent studies have focused on the possible role of microRNAs (small, noncoding RNAs) in viral infections, demonstrating that many host microRNAs are modulated to accomplish viral persistence, whereas others are modulated by the host to achieve viral clearance. For example, cellular microRNAs may influence HBV replication directly by binding to HBV transcripts or indirectly by targeting cellular factors relevant to the HBV life cycle. On the other hand, HBV infection can trigger changes in cellular microRNA expression associated with distinctive expression profiles, depending on the phase of liver disease. Changes in plasma microRNAs may also have a role in the persistence of HCV infection. HCV can subvert both pre-microRNA-122 and mature microRNA-122 to aid in the protection of the viral RNA genome from degradation by host cells. Furthermore, a microRNA signature, including microRNA pathways involved in cell proliferation, tissue regeneration, preservation of the epithelial phenotype and fibrogenesis, has been associated with progression of chronic viral hepatitis.
The role of vascular injury
Hepatocyte injury often precedes cirrhosis but is insufficient for its development. Even after significant hepatocyte necrosis, the liver can regenerate to a normal architecture without permanent fibrosis. Moreover, despite distribution of significant hepatocyte injury evenly throughout the hepatic lobule in chronic hepatitis, the formation of fibrous septa only occurs in limited regions. Some fibrous septa probably develop as scar tissue to replace bridging necrosis caused by direct hepatocyte injury. However, some septa form in response to regions of parenchymal extinction after injury and thrombosis of intrahepatic arteries and veins with resultant parenchymal atrophy. In chronic hepatitis this injury is probably a ‘bystander’ phenomenon, resulting from the inflammatory response directed against, but not limited to, the infected parenchymal cell. Once cirrhosis is established, stasis leads to further thrombosis of portal and hepatic veins and secondary parenchymal loss that is independent of the activity of the original disease.
Mechanisms of fibrogenesis and fibrosis regression
Scarring during chronic liver disease represents a balance between new deposition of matrix and its resorption. As long as the disease persists, the balance favours deposition and scar formation. If the disease is inhibited or eliminated, fibrosis and even cirrhosis can regress. The progression and resolution of fibrosis involve parenchymal and nonparenchymal liver cells, as well as infiltrating immune cells. Chronic hepatocyte death is a critical step of fibrogenesis, inducing activation of cell inflammatory and profibrogenic pathways. Dead hepatocytes release their cellular contents and generate reactive oxygen species (ROS) that activate resident macrophages (Kupffer cells) to release profibrogenic factors, especially TGFβ.
The principal cell responsible for collagen deposition and scar formation in the liver is the hepatic stellate cell (HSC), although it is becoming clear that this class of cells is highly heterogeneous and that other cells and processes, including portal myofibroblasts, epithelial-mesenchymal transition cells and marrow-derived cells, also may play significant roles. After liver injury, fibrogenic signals promote transdifferentiation of HSCs to proliferative and contractile myofibroblasts. The activation of HSCs into myofibroblasts is regulated by their interaction with several cell types. Indeed, besides injured hepatocytes, the hepatic macrophages, endothelial cells and lymphocytes drive HSC activation. Viral components may also directly contribute to fibrogenesis. For example, experimental evidence suggests that the HCV core protein, as well as nonstructural HCV proteins, may directly trigger HSC activation and thus the initiation of fibrogenesis. Oxidative stress, resulting from free-radical activity and decreased efficiency of antioxidant defences, plays a prominent role in the activation of HSCs.
Autophagy, a highly regulated intracellular pathway that preserves energy homeostasis, has recently been implicated in driving HSC activation by providing critical energy substrates through the hydrolysis of retinyl esters to generate fatty acids. The HSC that is primed by ‘initiating’ stimuli can then respond to a variety of cytokines that upregulate collagen synthesis and deposition, including TGFβ, IL-1 and IL-4, many of which are primarily or secondarily produced in inflammatory responses typical of chronic viral hepatitis.
Epigenetic regulation is important in controlling HSC activation, since regulatory events must occur quickly after injurious stimuli. Among epigenetic signals, microRNAs seem to play an important regulatory control in HSC activation and fibrosis, a discovery that opens new perspective in the field of antifibrotic therapy research.
Angiogenesis and sinusoidal remodelling are typical features of liver fibrogenesis. Hypoxia plays a crucial role in eliciting angiogenesis and, along with HSCs, is the most prominent source of vascular endothelial growth factor (VEGF) and angiopoietin-1. In chronic viral hepatitis the amount of angiogenesis and hepatic VEGF expression is associated with the grade of fibrosis. HCV may activate several pathways and systems implicated in angiogenesis. The core E1, NS3 and NS5A proteins induce mitochondrial dysfunction, resulting in generation of new ROS that leads to induction of hypoxia-inducible factor 1 (HIF1) and upregulation of VEGF. HBV can also influence angiogenesis. In particular, the regulatory protein X is able to stimulate angiogenesis directly through activation and stabilization of HIF1.
Regression of fibrosis requires breaking up and digestion of collagen and elastin fibres, which make up the principal components of the scar. Various metalloproteinases accomplish some, if not all, of these tasks and are produced by HSCs and other nonparenchymal cells, particularly those of macrophage lineage. However, the appearance of fractured, ‘perforated’ septa with hepatocytes within, or completely interrupting, the septa, usually in the absence of inflammation or activated macrophages, suggests that hepatocytes themselves may play a major role. Expression of various metalloproteinases by hepatocytes supports this concept.
Loss of activated HSCs is a central event in the resolution of liver fibrosis and may be caused by senescence and apoptosis. Cellular senescence is a genetically controlled program preventing cell division once cells exceed a finite proliferative capacity. Senescent HSCs are targeted by NK cells for clearance in vivo , thus contributing to fibrosis resolution. In animal models, apoptosis is the predominant clearance mechanism of activated HSCs, and an inverse association between HSC apoptosis and fibrosis has been observed in chronic HCV infection. Recent studies showed that HSCs can also revert to an inactive phenotype during liver fibrosis regression.
The extent to which fibrosis may regress is not yet fully clear. It has been observed that collagen cross-linking (which characterizes old fibrotic matrix) and presence of wide and paucicellular septa are critical determinants of fibrosis reversibility. Elastin deposition, as seen in advanced fibrosis/cirrhosis, may also contribute to the resistance to fibrosis reversion. On the other hand, recent fibrotic deposition, characterized by thin reticulin fibres and diffuse inflammatory infiltrate, is more likely to be fully reversible.
Multiple chronic viral infections
Co-infection by multiple hepatotropic viruses
Since hepatitis B, C and D viruses are all parenterally spread, it is not surprising that dual or triple infection of these viruses occurs. Viral interference appears to be most common in co-infections experimentally and clinically, usually HCV interfering with HBV replication, although the reverse has also been reported when HBV followed HCV infection. The clinical course, however, does not seem to be consistently altered by such co-infections, although case-fatality rates may be higher than in mono-infection.
Histopathologically, no specific findings suggest multiple infections, and the diagnosis depends on serological investigations. However, immunohistochemical studies have revealed suppression of HBV core antigen by simultaneous HCV infection. In a patient serologically positive for hepatitis B surface antigen (HBsAg), the absence of demonstrable tissue staining for HBV antigens may indicate that co-infection not only with HDV, but also with HCV, should be clinically suspected by the pathologist.
Co-infection by hepatotropic viruses and human immunodeficiency virus
Since HBV, HCV, HDV and HIV are all parenterally acquired, and HBV and HIV are also frequently transmitted sexually, co-infection of these hepatitis viruses and HIV is common. Additionally, co-infection between HIV and HAV has been identified, although this does not seem to lead to a difference in the severity of illness when HIV replication is controlled and host immunity is intact. With impaired immunity in late-stage HIV infection, mortality increases, and HAV viral levels may be higher and resolution delayed, compared to mono-infected individuals. HIV co-infection with HEV has been reported, and the course of HEV may be prolonged in the patient with impaired immune function.
Although acute hepatitis B is less frequently icteric in the patient with untreated HIV infection, viral persistence and development of chronic infection are more common. Most studies indicate diminished histological activity of chronic hepatitis B, although greater activity has also been reported. Reactivation of hepatitis B has also been reported with untreated HIV co-infection. Rarely, the fibrosing cholestatic variant of hepatitis B is seen, as in hepatitis C. With HDV, co-infection with HIV seems to worsen liver damage, as evidenced by increased serum transaminase levels and worsened histological severity. Replication of HBV both by itself and with HDV is increased and may be demonstrated by more diffuse staining for hepatitis B and delta antigens in tissue specimens.
Co-infection of HCV and HIV is also common. As HIV-infected individuals survive longer with new antiviral therapies, the importance of treating HCV infection in these patients increases. Acute hepatitis C seems to be more often symptomatic and much more likely to result in liver failure when HIV is simultaneously acquired. Many studies indicate that untreated HIV infection with significant immunosuppression increases the severity and accelerates the course of chronic hepatitis C, although successful anti-HIV treatment accompanied by immune reconstitution seems to lead generally to a more typical HCV course. Even with minimal or absent immunosuppression in such treated patients, however, fibrosis may still be more prevalent and more rapid, although the mechanism is uncertain. Conversely, it has also been suggested that HCV infection is a poor prognostic indicator for HIV disease, and patients with co-infection, even with successful immune reconstitution, have increased mortality and morbidity due to viral interactions directly or interactions with the many medications required to treat both infections. Fortunately, treatment of HCV in patients with HIV is now highly effective with direct-acting antiviral therapy. Efficacy of treatment is comparable to HCV mono-infected persons, and treatment options are similar, with special attention to potential antiviral drug–drug interactions.
Differential diagnosis of chronic hepatitis
Many disease states can mimic chronic viral hepatitis, and other, nonviral conditions can cause the same chronic hepatitic patterns of injury. To evaluate this fully in a biopsy or resection specimen, clinical history must be obtained. In all cases, if a diagnosis of chronic viral hepatitis is contemplated, serological tests for hepatitis B, C and D must be performed. In the absence of positive viral serology, other diseases must be considered.
Other causes of chronic hepatitis
Infecting viruses are not the only aetiology of the typical histological features of chronic hepatitis. Autoimmune hepatitis is characterized by hypergammaglobulinaemia and autoantibodies such as antinuclear antibodies or anti-liver–kidney microsome (LKM) antibodies (see Chapter 8 ). Histologically, abundant plasma cells in the inflammatory infiltrate and severe activity, i.e. confluent necrosis (perivenular or bridging necrosis or parenchymal collapse), suggest an autoimmune process rather than a viral infection. Serological studies demonstrating autoantibodies, in the absence of those confirming viral infection, should establish the diagnosis. However, one caveat is that in chronic hepatitis C, and less often in chronic hepatitis B, serological studies may indicate the presence of circulating autoantibodies (mostly non-organ specific) because chronic viral infection may lead to breakdown of self-tolerance and induction of autoantibodies. For example, chronic hepatitis B infection may stimulate the formation of circulating immune complexes of viral antigens and reactive antibody. These complexes may fix complement and induce tissue damage such as vasculitis, arthritis and glomerulonephritis. Chronic hepatitis C is also associated with autoimmune phenomena. HCV and less frequently HBV are associated with mixed cryoglobulinaemia. It is worth considering that most individuals with hepatitis C or B and non-organ-specific autoantibodies do not meet the diagnostic criteria for autoimmune hepatitis, and only a minority of patients are thought to present true overlap.
Metabolic diseases may also have chronic hepatitic patterns of injury. α1-Antitrypsin deficiency can have the same necroinflammatory lesions and pattern of scarring, but histological demonstration of α1-antitrypsin globules by H&E, PAS staining after diastase digestion or immunohistochemistry will confirm the diagnosis. Typically, liver disease is seen in individuals with ZZ phenotype. Phenotypes such as SS or a heterozygous pattern are not predictably related to chronic liver disease. Care must be taken, however, to exclude concomitant viral infection serologically; as in the setting of metabolic diseases, an increase in liver injury may be caused by a superimposed viral infection.
Similarly, Wilson disease can cause the same pattern of injury, but histological confirmation, while suggested by abundant Mallory–Denk bodies, fatty change or even some copper accumulation in periportal hepatocytes, can be achieved only in combination with clinical and biochemical findings. The diagnostic tests are complex, but low levels of serum caeruloplasmin, increased urinary copper or evidence of increased tissue stores of copper (by histochemical staining, or better by quantitative assessment of an adequate sample) are helpful. However, none of the test results is pathognomonic for Wilson disease and may be abnormal in patients with other causes of abnormal copper retention, such as primary biliary cirrhosis or primary sclerosing cholangitis. Wilson disease should be remembered as a confounding impostor and considered in the differential diagnosis of nonviral chronic liver disease irrespective of age.
Some drugs can also cause chronic hepatitis, including: α-methyldopa, isoniazid, oxyphenisatin, nitrofurantoin and diclofenac (see Chapter 12 ). Some of these drugs may actually induce autoantibodies, suggesting induction of an autoimmune hepatitis. Again, the absence of serological markers of viral infection will help diagnostic accuracy, and careful history taking will often reveal the offending toxin.
Diseases that mimic chronic viral hepatitis
Any disease leading to dense lymphoplasmacytic infiltrate in the portal tracts may mimic chronic viral hepatitis. For example, primary biliary cholangitis (or cirrhosis) (PBC) not only often has a dense portal infiltrate, but may also have foci of interface and lobular hepatitis. A diagnostic biopsy for PBC demonstrating granulomatous destruction of bile ducts is unlikely to cause this confusion. A later-stage lesion, with prominent ductular reaction and features of chronic cholestasis adjacent to fibrotic septa, is also unlikely to cause confusion. However, nondiagnostic early lesions of PBC may be difficult to distinguish from chronic viral hepatitis, particularly hepatitis C, because hepatitis may have marked bile duct damage and even loss. In these cases, clinical correlation is important, since PBC is predominantly characterized by marked elevation of ALP and GGT, increased serum IgM, as well as antimitochondrial (or other) autoantibodies. ALT/AST values are generally less than five times the upper limit of normal, although these may fluctuate to higher levels. Similar confusion may be encountered, but less frequently, with a nondiagnostic biopsy specimen for primary sclerosing cholangitis. Again, clinical correlation is essential, evaluating possible chronic inflammatory bowel disease (usually ulcerative colitis) and characteristic bile duct abnormalities on imaging studies.
Lymphoma or leukaemic infiltrates may also mimic the inflammatory infiltrate of chronic viral hepatitis, particularly when the infiltrate is most prominently portal with overflow into neighbouring sinusoids. In such cases, careful inspection of the lesion will reveal an absence of true interface hepatitis at the margins of portal tracts, where the malignant cells extend past hepatocytes that are atrophic but not truly apoptotic. Similarly, parenchymal hepatocytes may appear atrophic, but acidophil bodies are generally absent. The typical scarring of progressive chronic hepatitis is also not usually present in such specimens. Most importantly, the infiltrating cells will have features suggesting a lymphoproliferative disorder, including monomorphism or marked atypia.
Semiquantitative scoring in chronic hepatitis
Application of scoring systems
The first scoring system specifically designed for the study of chronic hepatitis was developed by Knodell et al. It was modified by Ishak et al. in 1995 ( Tables 6.5 and 6.6 ), as well as by Batts and Ludwig ( Table 6.7 ) and the METAVIR cooperative group of French investigators ( Fig. 6.22 ). These remain the most frequently used systems, and all have advantages and disadvantages.