Renal · Glomerulonephritis
The facts most likely to be tested
Membranous nephropathy is the most common cause of nephrotic syndrome in Caucasian adults.
The pathophysiology involves subepithelial immune complex deposition leading to glomerular basement membrane (GBM) thickening.
Light microscopy reveals diffuse capillary and GBM thickening without significant hypercellularity.
Silver stain (Jones stain) demonstrates the classic spike and dome appearance caused by GBM material protruding between immune deposits.
Immunofluorescence shows granular deposits of IgG and C3 along the capillary loops.
Primary membranous nephropathy is most commonly associated with autoantibodies against the phospholipase A2 receptor (PLA2R).
Secondary causes are frequently linked to solid organ malignancies, SLE, hepatitis B, or medications like NSAIDs.
Vignette unlocked
A 55-year-old male presents to the clinic with a two-week history of progressive lower extremity edema and frothy urine. Physical examination reveals 3+ pitting edema to the knees and a blood pressure of 145/90 mmHg. Laboratory studies show a serum albumin of 2.8 g/dL, a total cholesterol of 320 mg/dL, and a 24-hour urine protein excretion of 5.5 g. Renal biopsy is performed, and silver staining reveals diffuse GBM thickening with a spike and dome pattern.
Which of the following is the most likely underlying pathophysiology of this patient's condition?
Subepithelial immune complex deposition
The vignette describes classic nephrotic syndrome with a biopsy showing the 'spike and dome' pattern, which is pathognomonic for membranous nephropathy caused by subepithelial immune complex deposition.
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High yield triage
Etiology / Epidemiology
Most common cause of nephrotic syndrome in Caucasian adults; 70% are primary (idiopathic) due to anti-PLA2R antibodies.
Clinical Manifestations
Presents with nephrotic syndrome (edema, hypoalbuminemia, hyperlipidemia); spike and dome appearance on biopsy.
Diagnosis
Renal biopsy is the gold standard; shows thickened glomerular basement membrane with subepithelial deposits.
Treatment
ACE inhibitors or ARBs for proteinuria; cyclophosphamide or rituximab for high-risk patients.
Prognosis
High risk of renal vein thrombosis; 30-40% progress to end-stage renal disease without treatment.
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Epidemiology & Etiology
Primary disease is autoimmune, mediated by anti-PLA2R antibodies. Secondary causes include malignancy (solid tumors), SLE, infections (HBV, HCV), and drugs like NSAIDs or gold.
Pertinent Anatomy
The pathology is localized to the glomerular basement membrane (GBM). Immune complex deposition occurs in the subepithelial space, leading to diffuse thickening without significant hypercellularity.
Pathophysiology
Circulating immune complexes deposit in the subepithelial space, activating the complement membrane attack complex (C5b-9). This causes podocyte injury, resulting in massive proteinuria and loss of glomerular filtration integrity.
Clinical Manifestations
Patients present with classic nephrotic syndrome: edema, hypoalbuminemia, and hyperlipidemia. Renal vein thrombosis is a major complication due to loss of antithrombin III. Look for flank pain and hematuria as red flags for thrombosis.
Diagnosis
Renal biopsy is required for definitive diagnosis. Light microscopy shows diffuse GBM thickening. Immunofluorescence reveals granular IgG and C3 deposits along the capillary loops.
Treatment
Initial management focuses on ACE inhibitors or ARBs to reduce proteinuria and blood pressure. High-risk patients require immunosuppression with rituximab or cyclophosphamide. Avoid nephrotoxic agents and monitor for infection during immunosuppressive therapy.
Prognosis
Approximately 33% of patients undergo spontaneous remission, while 33% progress to end-stage renal disease. Long-term monitoring of serum creatinine and urine protein-to-creatinine ratio is mandatory.
Differential Diagnosis
Minimal Change Disease: normal light microscopy, foot process effacement only
Focal Segmental Glomerulosclerosis: segmental sclerosis on biopsy, often associated with HIV/heroin
Diabetic Nephropathy: Kimmelstiel-Wilson nodules, history of long-standing diabetes
Amyloidosis: apple-green birefringence on Congo red stain
Lupus Nephritis: positive ANA/dsDNA, full-house immunofluorescence