ESSENTIALS OF DIAGNOSIS
Varying degrees of proteinuria, may have nephrotic syndrome.
Associated with coagulopathy, eg, renal vein thrombosis, if nephrotic syndrome present.
“Spike and dome” pattern on kidney biopsy from subepithelial deposits.
Secondary causes notably include hepatitis B virus and carcinomas.
Membranous nephropathy is the most common cause of primary nephrotic syndrome in adults, most often presenting in the fifth and sixth decades. It is an immune-mediated disease characterized by immune complex deposition in the subepithelial portion of glomerular capillary walls. The antigen in the primary form of the disease appears to be a phospholipase A2 receptor (PLA2R) on the podocyte in 70–80% of patients. Secondary disease is associated with underlying carcinomas (some of these cases may involve autoimmunity to podocyte-expressed thrombospondin type-1 domain-containing 7A [THSD7A]); infections, such as hepatitis B and C, endocarditis, and syphilis; autoimmune disease, such as SLE, mixed connective tissue disease, and thyroiditis; and certain drugs, such as NSAIDs and captopril. The course of disease is variable, with about 50% of patients progressing to ESRD over 3–10 years. Poorer outcome is associated with concomitant tubulointerstitial fibrosis, male sex, elevated serum creatinine, hypertension, and proteinuria greater than 10 g/day.
Patients with membranous nephropathy and nephrotic syndrome have a higher risk of hypercoagulable state than those with nephrosis from other etiologies; there is a particular predisposition to renal vein thrombosis in these patients.
Patients may be asymptomatic or may have edema or frothy urine. Venous thrombosis, such as an unprovoked deep venous thrombosis, may be an initial sign. There may be symptoms or signs of an underlying infection or neoplasm (especially lung, stomach, breast, and colon cancers) in secondary membranous nephropathy.
Hypoalbuminemia and hyperlipidemia are characteristic laboratory findings in the nephrotic syndrome. Evaluation for secondary causes including serologic testing for SLE, syphilis, and viral hepatidites, and age- and risk-appropriate cancer screening should be performed. Serum evaluation for circulating PLA2R antibodies to assess for idiopathic membranous nephropathy is possible; additionally, titers can be followed during treatment. Renal biopsy is indicated for all glomerular diseases except for classical presentations of diabetic nephropathy and minimal change disease. Biopsy findings in membranous nephropathy include increased capillary wall thickness without inflammatory changes or cellular proliferation (eFigure 22–15); when stained with silver methenamine, a “spike and dome” pattern results from projections of excess GBM between the subepithelial deposits (eFigure 22–16). Immunofluorescence shows IgG and C3 staining along capillary loops (eFigure 22–17). Electron microscopy shows a discontinuous pattern of dense deposits along the subepithelial surface of the basement membrane.
Membranous glomerulonephritis. (H&E stain.) (Used, with permission, from Jean Olson, MD.)