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MIDD Light Chain Deposition — ESENeph MCQ

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HardGlomerulonephritisMIDD Light Chain DepositionESENeph

A 35-year-old man with previously normal renal function presents with AKI (creatinine 600 umol/L) and nephrotic syndrome. He has a monoclonal IgG kappa paraprotein. Biopsy shows non-amyloid monoclonal Ig deposits along tubular and glomerular basement membranes (linear staining for kappa light chain and IgG on IF). Congo red is negative. What is the diagnosis?

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Correct answer: E — Monoclonal immunoglobulin deposition disease (MIDD/LCDD)

Linear monoclonal Ig deposits (typically kappa light chain) along basement membranes (TBM and GBM) with Congo red-negative, non-fibrillar granular deposits on EM is diagnostic of monoclonal immunoglobulin deposition disease (MIDD), specifically light chain deposition disease (LCDD) if light chain dominant. Unlike AL amyloidosis (Congo red positive, fibrillar), MIDD has granular non-fibrillar deposits. Unlike cast nephropathy (intratubular casts), MIDD has basement membrane deposition. Treatment targets the underlying clone (Bortezomib-based regimens).

Reference: KDIGO 2021 – GN Guideline; Leung et al 2012 – MIDD Review