Membranous Nephropathy (Membranous Glomerulopathy) (Study Ou…
Membranous Nephropathy (Membranous Glomerulopathy) (Study Outline) 1. Background Definition: A nephrotic syndrome characterized by immune complex deposition along the glomerular basement membrane (GBM) leading to GBM thickening. Epidemiology: Most common cause of nephrotic syndrome in non-diabetic adults. Pathophysiology: Immune complex deposition → complement activation (MAC-mediated podocyte injury) → proteinuria. Etiologies: Primary (idiopathic): associated with anti–PLA2R antibodies (high-yield). Secondary: Infections: hepatitis B/C, syphilis. Autoimmune: SLE. Malignancies (solid tumors). Medications: NSAIDs, gold, penicillamine. Course: May remit spontaneously; may progress to CKD/ESRD. 2. History Edema: insidious onset; peripheral ± periorbital. Foamy urine from heavy proteinuria. Possible systemic symptoms depending on secondary causes: Arthralgias, rash (SLE). Weight loss/night sweats (malignancy). Chronic hepatitis symptoms. Thromboembolism risk: elevated; renal vein thrombosis is classic high-yield association. 3. Exam Findings Edema: pitting, may be generalized. Possible hypertension (less pronounced early). Signs of secondary disease: Hepatomegaly/jaundice (hepatitis). Malar rash or alopecia (SLE). Lymphadenopathy or cachexia (malignancy). Pleural effusions/ascites in advanced nephrotic states. 4. Making the Diagnosis Urinalysis: Nephrotic-range proteinuria (>3.5 g/day). Lipiduria with fatty casts, oval fat bodies. Blood tests: Hypoalbuminemia, hyperlipidemia. Consider anti-PLA2R antibody testing in suspected primary disease. Serologic tests for secondary causes: ANA, hepatitis B/C serologies, syphilis testing, age-appropriate malignancy screening. Imaging: usually normal kidney size. Renal biopsy (Gold Standard): Diffuse GBM thickening on light microscopy. “Spike and dome” appearance on silver stain (high-yield). Granular IgG/C3 deposits on immunofluorescence. Key distinction: Minimal change disease has normal light microscopy; membranous has GBM thickening. 5. Management (Exam Concepts) General nephrotic syndrome principles: Conceptual sodium restriction; monitor fluid status and renal function. Avoid nephrotoxins and adjust renally cleared medications. Proteinuria reduction: RAAS modulation principles to reduce intraglomerular pressure (high-yield exam concept). Immunosuppression concepts: Indicated in persistent or severe proteinuria or declining GFR (no regimens). Secondary cause management: Treat underlying hepatitis, autoimmune disease, or malignancy at exam-concept level. Hyperlipidemia management: conceptual lipid-lowering. Thrombosis risk: recognize high risk for renal vein thrombosis in nephrotic patients. Follow-up: monitor for spontaneous remission vs. progression toward CKD. Referral: essential for biopsy interpretation, immunologic workup, and specialized management. QUESTION A 58-year-old man presents with increasing leg swelling and frothy urine for the past month. He denies fever, rash, joint pain, or recent travel. Medical history includes osteoarthritis, for which he takes ibuprofen regularly. Physical exam reveals bilateral pitting edema up to the mid-shin. Blood pressure is 138/86 mmHg. Laboratory findings: Serum albumin: 2.3 g/dL Total cholesterol: 312 mg/dL Urinalysis: 4+ protein, fatty casts, no hematuria 24-hour urine protein: 7.1 g Hepatitis B/C serologies: negative ANA: negative Serum creatinine: 1.1 mg/dL Renal biopsy shows diffuse glomerular basement membrane thickening with granular IgG and C3 deposits on immunofluorescence and a “spike and dome” appearance on silver stain. Which of the following best explains this patient’s pathophysiology? A) Immune complex deposition causing subepithelial podocyte injuryB) T-cell cytokine–mediated podocyte effacementC) Autoantibody-mediated attack on mesangial antigensD) C3 nephritic factor–mediated dense deposit formation