Chronic pancreatitis

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Chronic pancreatitis





Definition




Although the lost function can be replaced with pancreatic enzymes and management of diabetes mellitus, the most challenging symptom is pain.


Ammann et al. suggested that acute pancreatitis and chronic alcoholic pancreatitis are different stages of the same disease.1,2 Chronic pancreatitis represents the persistent damage after episodes of severe acute pancreatitis.3,4


The classification of CP as an separate disease was described in 1946 by Comfort et al.5 Since then, different classifications of CP have been presented. According to the Marseille Classification, CP is characterised by histological changes, persisting after the aetiologic agent has been removed.6 The Cambridge Classification (1983) defined CP as an ongoing inflammatory disease characterised by irreversible structural changes associated with abdominal pain and permanent loss of function.


In the Marseille–Rome classification of 1988 obstructive chronic pancreatitis, chronic inflammatory pancreatitis (with loss of exocrine parenchyma and replacement by fibrosis) and the chronic calcifying pancreatitis were described.


Recently, a new classification of CP has been suggested. Probable CP is characterised by a typical history and one or more of the following criteria: recurrent or persistent pseudocysts, ductal alterations, endocrine insufficiency (abnormal glucose tolerance test) or pathological secretin test. Definite CP is characterised by a typical history and at least one of the following criteria: typical histology from an adequate surgical specimen, moderate or marked ductal alterations, pancreatic calcification, marked exocrine insufficiency defined as steatorrhea, normalised or markedly reduced by enzyme substitution.7




Aetiology


Chronic pancreatitis is a highly complex process that begins with episodes of acute pancreatitis and progresses to end-stage fibrosis at different rates in different people due to different mechanisms. The most frequent causes are excess alcohol consumption (70–90%),9 cholelithiasis, autoimmune or individual genetic predisposition and anatomical variants such as pancreas divisum (Box 14.1).



In up to 20% of patients the reasons or predisposing factors are not identifiable. The peak presentation of the disease occurs in patients between 35 and 55 years of age. Long-term consumption of alcohol is associated with an increased risk of developing CP. The precise level of daily alcohol intake at which patients are at risk for developing CP has not been clearly recognised, but it is estimated at 60–80 g per day, although individual sensitivity to the toxic effects of alcohol varies. Women are at greater risk, as are non-Caucasians when compared to their Caucasian counterparts. High caloric intake of protein and fat, smoking and lack of vitamins and trace elements have been described as additional predisposing risk factors.



Clinical course


Recurrent episodes of abdominal pain is the main symptom of CP, leading to inability to work, early retirement and addiction to analgesics. Severe pain attacks are the leading causes for hospitalisation. In most patients, pain is characterised as deep, penetrating, radiating to the back, and mostly worse after meals. Pain is frequently nocturnal, usually felt centrally in the epigastric region or subcostally with radiation to the back or shoulder tip, and is often eased by leaning forward or lying down to one side with knees pulled up, the so-called ‘jack-knife’ position. Ammann et al. described two different types of pain. The first, type A, is characterised by recurrent bouts of short-term, relapsing pain episodes. Type B pain is characterised as prolonged and persistent, and it is associated with secondary complications of CP such as pseudocysts or biliary obstruction. The natural course of CP is characterised by a consecutive loss of pancreatic parenchyma by fibrosis leading to exocrine insufficiency with diarrhoea, steatorrhoea, malnutrition and weight loss. In advanced stages, patients may present with endocrine insufficiency (diabetes mellitus). The clinical course and histomorphological changes that characterise the disease are extremely variable. Overall, life expectancy is shortened by 10–20 years. The mortality is increased 3.6-fold compared with a population without CP. The annual treatment costs are approximately $17 000 per patient.


The inflammation leads to progressive and irreversible loss of functional parenchyma and replacement with fibrotic tissue. The ductal system displays strictures of the bile duct, and duodenal stenosis10 or the formation of pancreatic pseudocysts. Furthermore, CP can result in intraductal or parenchymal calcifications of the pancreas.



The natural course is that most patients with long-standing CP will become pain free due to a progressive ‘burning out’ of the organ.12,13 Episodes of pain may occur less frequently, whereas endocrine and exocrine insufficiency commonly worsens. The pancreatic parenchyma is irreversibly converted to fibrous tissue with associated diabetes and steatorrhoea.14


At the time of onset of CP, 8% of patients have at least a moderate degree of endocrine insufficiency, whereas in long-term follow-up approximately 80% have endocrine insufficiency.15,16 Studies have shown that it takes 10–20 years of a progressive inflammatory process to cause exocrine insufficiency by destroying the pancreatic parenchyma.17,18



At least 50–68% of patients with CP need surgery for management of complications or for intractable pain.20 Although spontaneous relief occurs, the effects of chronic pain can have lasting repercussions including depression, opiate addiction, unemployment and social alienation exacerbated by the stigma of alcoholism.


Reduction of alcohol intake does not influence the course of pain in chronic alcoholic pancreatitis, but continued alcohol abuse is associated with significantly lower survival rates. Patients that stop drinking may get some improvement in exocrine function.21 Endocrine insufficiency does not alter the course of pain. For the individual patient, the course of the disease is unpredictable.2123



Pathophysiological findings and pain mechanisms in chronic pancreatitis


Despite the advances in our understanding of pathophysiology there is still no therapy directed toward the inflammatory process that leads to the regression of the disease. Therefore, symptom control is the primary aim of treatment. Several theories about the course of pain have been proposed but it is extremely multifactorial and variable between patients.



The acinar cells are directly damaged by alcohol. A change in microcirculatory perfusion and alterations in epithelial permeability lead to an imbalance in the pancreatic juice, and decreased fluid or bicarbonate secretion. Parenchymal necrosis of the pancreas may induce perilobular fibrosis that leads to intralobular fibrosis, ductal obstruction and periductal inflammation. Altered amounts of lithostatin in the pancreatic juice can lead to formation of protein plugs and stones in ducts and ductules.24


Pathomorphological findings in CP such as inflammatory infiltration of the pancreatic tissue, fibrosis, atrophy of the acinar cells, calcifications, pancreatic duct strictures and pseudocysts can affect focal segments of the gland, or be a diffuse finding throughout the whole organ.


Histomorphologically different forms of CP can be distinguished.



Calcifying CP


The most common form (calcifying CP) is characterised by recurrent bouts of acute pancreatitis with abdominal pain and development of intraductal calculi, protein plugs and parenchyma calcifications. These alterations of various degrees in different stages of the disease lead to pancreatic duct stenosis and consecutively to prestenotic duct dilatation. Additionally, epithelial alterations, inflammatory periductal infiltrations, parenchymal atrophy, necrosis and fibrosis can be found.25


Obstructive CP is often painless and caused by blockage of the main pancreatic duct due to tumour or an inflammatory process (post-acute pancreatitis) that leads to atrophy of the pancreatic tissue and prestenotic duct dilatation. No alteration of the ductal epithelium is found.26 Pancreatic duct stones are uncommon. Periductal fibrosis and inflammatory infiltration are mainly found around the larger ducts and in the pancreatic head. Diffuse fibrotic changes occur throughout the organ without lobular topography. Pancreatic main-duct stenosis may be caused by papillary stenosis (tumour) or inflammation, duodenal diverticula, pancreatic tumours, congenital or acquired duct abnormalities (pancreas divisum), or rarely by traumatic pancreatic duct injuries. Small-duct pancreatitis is an extremely rare form of CP that is defined as main duct diameter ≤ 3 mm, with fibrous and inflammatory tissue.27



Autoimmune pancreatitis


Autoimmune pancreatitis is characterised by the absence of typical risk factors for developing CP or hereditary factors. In the past this subtype was named primary inflammatory sclerosis of the pancreas, non-alcoholic duct destructive pancreatitis or lymphoplasmacytic sclerosing pancreatitis.28–30 The term autoimmune pancreatitis was introduced by Yoshida et al. in 1995.31 Autoimmune pancreatitis can present with a focal event or with multiple lesions. Pseudocysts and caliculi are rarely found. Four histological features are characteristic of autoimmune pancreatitis. Lymphoplasmacytic infiltration, consisting of lymphocytes and plasma cells (often with high levels of IgG4), macrophages, neutrophils and eosinophils result in an intestinal fibrosis.32 Additionally, periductal inflammation and periphlebitis can lead to luminal strictures or obliterative venulitis, respectively. Obstructive jaundice is caused by an effect on the common bile duct that may extend to the gallbladder and biliary tree. An increased level of IgG4 is a sensitive marker.33 Autoimmune pancreatitis is associated with other autoimmune disorders such as ulcerative colitis, Crohn’s disease, primary sclerosing cholangitis, Sjörgren’s syndrome, lymphocytic thyroiditis and primary biliary cirrhosis.34



Hereditary CP


Hereditary chronic pancreatitis (HCP) is a rare form with an incidence of approximately 3.5–10 per 100 000 inhabitants.35 The morphological findings in HCP are irregular sclerosis with focal, segmental or diffuse destruction of the parenchyma. Different mutations have been detected to be associated with HCP, most commonly R122H, an N291 mutation of the PRSS1 gene, and mutations of the CFTR and SPINK1 genes.36 The risk of developing pancreatic cancer is increased in HCP with PRSS1 mutation as compared with the normal population and chronic alcoholic pancreatitis.


Rare reasons for CP besides pancreatic duct obstruction due to tumours, strictures, diverticula and anatomical variations like pancreas divisum or annular pancreas are trauma and genetic mutation.




Pathogenesis of pain in chronic pancreatitis


Pain is the cardinal symptom in patients with CP. Together with often ongoing consumption of alcohol, it is most difficult to treat. The permanent pain impairs quality of life, leads to addiction to analgesics and results frequently in unemployment or early retirement.


In the initial stage of the disease the pain is intermittent and recurrent; later it persists. Painless pancreatitis is found rarely in alcohol-induced pancreatitis (< 10%), while pain-free periods are seen in late-onset idiopathic pancreatitis.37


The formation of duct dilatation and hypertension due to downstream obstruction of the pancreatic duct is the most widely accepted hypothesis for the cause of pain in CP.


Ebbehoj et al. found a significantly higher pancreatic tissue pressure in patients who had painful CP compared with pain-free controls. These findings are interesting but have not been reproduced by other investigators. The reason for increased pressure can be due to postinflammatory scarring of the pancreatic (main and side) ducts, pancreatic duct stones or stricture or haemosuccus pancreaticus that leads to obstruction. Other reasons are pancreatic abscess, ascites, bile duct stenosis or duodenal stenosis. Patients with a reduced intraductal pressure had better pain relief compared to patients with higher intraductal pressure.38 The assessment of pain is very difficult. Most trials in CP use classifications for description of pre- and postoperative pain or outcome such as excellent (no pain), good (better), fair (nil) and poor (worse); therefore, no comparison between different trials is possible. Pain relief is more common in patients that quit drinking. The underlying mechanism for pain in CP is poorly understood. Different concepts have been hypothesised, but none of them can completely explain the pain in this disease.



Additionally, it has been reported that phenotypic modification of primary sensory neurons may play a role in causing persistent pain. Focal release and uptake of mediators in the peptidergic nerves have been shown to be changed by initial pancreatic inflammation. Previous trials revealed that the number and diameter of the pancreatic nerves, as well as activity, are significantly increased in patients with CP. A correlation between pain and expression of growth-associated protein 43 and level of methionine-enkephalin was detected. It is hypothesised that increased pressure facilitates the influx of pain mediators into the nerves and causes a neuritis resulting in pain.


Another hypothesis is that pancreatic ischaemia is responsible for the pain. Ischaemia activates xanthine oxygenase, leading to toxic oxygen metabolites. An increased level of cytochrome P450 in patients with CP was found in several trials but treatment with an inhibitor of xanthine oxygenase did not reduce the pain.


It is also likely that an individual’s genetics plays a role in the overall pain experience. Genetic polymorphisms have been associated with disparate postoperative pain sensation and response to narcotics. Unfortunately, examination of candidate gene polymorphisms in visceral pain syndromes has been less convincing and clear evidence is lacking (Box 14.2).




Preoperative assessment and investigations


A thorough history and physical examination is pivotal for the diagnosis and adequate therapy of patients with CP. The evaluation of aetiological factors is essential to select patients for the different therapeutic options.



Laboratory evaluation


Beside routine variables, laboratory data should include cholestasis parameters and tumour markers for pancreatic carcinoma. Endocrine and exocrine function has to be evaluated. Typically, serum lipase and amylase levels are markedly elevated in the acute setting, but may be normal in CP as a result of severe acinar atrophy. The presence of leucopenia and thrombocytopenia suggests that splenic vein thrombosis may have resulted in hypersplenism. Some studies have shown an elevated serum cholecystokinin (CCK) level in CP patients. It is proposed that CCK may increase pancreatic enzyme secretion. Trypsin levels are particularly high in patients with alcoholic pancreatitis, even when amylase levels are normal. In patients with autoimmune pancreatitis, the IgG and in particular its subtype IgG4 will be raised, the latter having a sensitivity and specificity as high as 95–97%, respectively.



Imaging studies


For tailored therapy and especially for planning surgical therapy, imaging studies play a central role in the diagnostic work-up of CP patients.


Abdominal ultrasound is an effective method that may help to establish the diagnosis. The use of endoscopic ultrasound is more sensitive and specific. Many patients undergo multiple endoscopic retrograde cholangiopancreatography (ERCP) procedures for diagnosis and therapeutic interventions. The gold standard in diagnosis of CP and for the planning of surgical therapy is contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI). MRI offers the additional possibility to evaluate the ductal system by magnetic resonance cholangiopancreatography (MRCP). The advantage of CT is the better visualisation of parenchymal calcifications. Positron emission tomography (PET) may be helpful to differentiate between CP and pancreatic cancer (Box 14.3).




Treatment


The treatment of CP and its complications remains a major challenge. The most distressing symptom is intractable pain with continual abuse of analgesics.




Conservative therapy


The basis of adequate management of CP includes reduction of risk factors, replacement therapy for exocrine and endocrine insufficiency and nutritional supplementation, as well as pain therapy. Medical therapies such as dietary alterations, analgesics (non-steroidal anti-inflammatory drugs, paracetamol, prednisolone, dextropropoxiphene, tricylic antidepressives and in the late stages opioids), oral enzyme supplements and somatostatin analogues may improve symptoms. An important aspect in the treatment of CP patients is a multidisciplinary approach. Alternative therapies such as psychiatric or psychological input, transcutaneous electronic nerve stimulation, acupuncture, intrathecal pumps for opioids and spinal cord stimulation may be beneficial as adjunctive treatment (Box 14.4).


May 31, 2016 | Posted by in HEPATOPANCREATOBILIARY | Comments Off on Chronic pancreatitis
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