Parenchymal Renal Disease
Gerald B. Appel
POINTS TO REMEMBER:
Findings on urinalysis that point to a glomerular origin include erythrocyte casts and dysmorphic erythrocytes.
The nephrotic syndrome (NS) is defined by more than 3.0 to 3.5 g of proteinuria daily accompanied by hypoalbuminemia, edema, and hyperlipidemia. Nephrotic proteinuria is predominantly due to albuminuria and always denotes a glomerular origin of the disease process.
The initial evaluation of the patient with NS includes laboratory tests to define whether the patient has a primary, idiopathic, or a secondary form of NS [e.g., measurement of fasting blood sugar, antinuclear antibodies, serum complement, hepatitis B virus, hepatitis C virus (HCV), and HIV serology]. Once secondary causes have been excluded, the treatment of the adult nephrotic patient usually requires a renal biopsy to define the pattern of glomerular involvement.
Minimal-change disease (MCD) is the most common pattern of idiopathic NS in children and comprises approximately 5% of idiopathic NS in adults. Patients typically present with sudden onset of weight gain and both periorbital and peripheral edema.
Membranous nephropathy (MN) is the most common pattern of idiopathic nephrotic syndrome in white Americans, while focal segmental glomerulosclerosis (FSGS) is the most common in African Americans.
The presence of sudden flank pain, deterioration of renal function, or symptoms of pulmonary emboli in a patient with MN should prompt an investigation for renal vein thrombosis.
In certain elderly patients with MN, an underlying carcinoma may be the occult cause of the renal lesion.
Complement levels and the results of other serologic tests are normal in FSGS. Serum levels of suPAR, the soluble urokinase receptor, have been found to be elevated in FSGS patients as opposed to proteinuric patients with other forms of NS.
Most patients with idiopathic NS, whether due to MN, FSGS, or MCD, will respond to immunosuppressive regimens with a remission of the nephrotic syndrome. Blockade of the renin-angiotensin-aldosterone system (RAAS) will reduce proteinuria in all nephritic patients.
IgA nephropathy is the most common pattern of idiopathic glomerulonephritis worldwide.
The diagnosis of IgA nephropathy is established by finding glomerular IgA deposits either as the dominant or as the codominant immunoglobulin on immunofluorescence (IF) staining. In addition to IgA, deposits of C3 and immunoglobulin G (IgG) are common.
IgA nephropathy often presents with one of two syndromes: asymptomatic microscopic hematuria and/or proteinuria (most common in adults), or episodic gross hematuria after upper respiratory tract infections or exercise (most common in children).
Evidence supports using RAAS blockade in all proteinuric IgA nephropathy patients and corticosteroids in those with larger amounts of proteinuria.
Rapidly progressive glomerulonephritis (RPGN):
RPGN includes glomerulonephritides with progression to renal failure in a matter of days to weeks and the presence of extensive extracapillary proliferation (i.e., crescent formation) in a large percentage of the glomeruli.
RPGN has been divided into three patterns, defined by immunologic pathogenesis: Those characterized by anti-GBM disease, those characterized by immune complex deposition (e.g., SLE and poststreptococcal GN), and those characterized by the absence of immune deposits or anti-GBM antibodies (i.e., pauciimmune).
Most cases of pauciimmune RPGN have circulating antineutrophil cytoplasmic antibodies (ANCA-positive RPGN).
Pauciimmune RPGN has the most favorable treatment response rate of all patterns of RPGN.
Many patients with parenchymal disease due to acute (AIN) and chronic interstitial nephritis (CIN) will have medication-related disease.
When eosinophils comprise more than 5% of the total urinary leukocytes it is strongly suggestive of AIN. Eosinophiluria may also occur in RPGN, cystitis, and prostatitis.
The chronic use of analgesics (e.g., nonsteroidal anti-inflammatory drugs) have been associated with CIN.
Glomerular involvement in HIV infection:
Infection with this virus has been associated with a number of patterns of renal disease, including acute renal failure, interstitial nephritis, and a unique form of glomerulopathy now called HIV-associated nephropathy (HIVAN).
Classic clinical features of HIVAN include a higher incidence among blacks, heavy proteinuria (usually with NS), renal insufficiency, and a rapid progression to ESRD with large echogenic kidneys on ultrasonography.Related posts:
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