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- The clinical features of nephrotic syndrome are present.
- The glomeruli are not inflamed.
- The glomerular capillary basement membrane appears thickened.
- There is an absence of glomerular inflammation.
- Idiopathic membranous nephropathy (MN) is relatively common and remains the leading cause of nephrotic syndrome in white adults. It is diagnosed by ruling out secondary causes.
- Secondary MN forms may account for up to one-third of cases and are associated with autoimmune diseases.
- Malignancy increases with increasing age.
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Sixty years ago E.T. Bell coined the term membranous glomerulonephritis to describe the renal pathology of a group of patients with the clinical features of nephrotic syndrome in whom the glomeruli were not inflamed but in whom the glomerular capillary basement membrane appeared thickened. The synonymous terms extramembranous nephropathy and epimembranous glomerulonephritis have also been used to describe the disease. The word glomerulonephritis is, however, misleading as one of the main features of the condition is the absence of glomerular inflammation; because of this the word nephropathy is more often employed.
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Idiopathic MN is a relatively common immune-mediated glomerular disease and remains the leading cause of nephrotic syndrome in white adults. In the majority of cases, the etiologic agent is unknown, and the disorder is termed idiopathic. Secondary MN forms may account for up to one-third of cases and are associated with autoimmune diseases (eg, systemic lupus erythematosus, SLE), infections (eg, hepatitis B and C), medications [eg, nonsteroidal antiinflammatory drugs (NSAIDs), d-penicillamine, gold], and neoplasias (eg, colon cancer, kidney cancer) (Table 26–1). The association with malignancy increases with age, reaching up to 20% in patients over the age of 60 years. Since idiopathic and secondary forms have similar clinical presentations, the designation of idiopathic is made by ruling out secondary causes by a careful history, physical examination, and laboratory evaluation of the patient. The disease is rare in children, and when it does occur, is commonly associated with an immunologically mediated disorder such as SLE.
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There is considerable evidence to support the hypothesis that idiopathic MN is an autoimmune disease. However, the pathogenic mechanisms that cause immune deposits of immunoglobulin G (IgG) and ...