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LCDD Linear Kappa Light Chain Deposits — ESENeph MCQ

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HardGlomerulonephritisLCDD Linear Kappa Light Chain DepositsESENeph

A 40-year-old man presents with nephrotic syndrome. He has no systemic symptoms. Renal biopsy shows mesangial expansion with periodic acid-Schiff (PAS)-positive deposits. Congo red stain is negative. Immunofluorescence shows monotypic kappa light chain deposition along the tubular basement membranes, Bowman's capsule, and glomerular basement membrane in a linear pattern. Serum free light chains show elevated kappa with abnormal ratio. What is the diagnosis?

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Correct answer: C — Light chain deposition disease (LCDD)

The combination of monotypic (kappa) light chain deposition in a LINEAR pattern along tubular basement membranes, Bowman's capsule, and GBM — with Congo red negativity — is diagnostic of light chain deposition disease (LCDD), a monoclonal gammopathy of renal significance (MGRS). Unlike AL amyloidosis (which is Congo red positive with fibrillar deposits), LCDD has non-fibrillar, granular deposits that do not form amyloid fibrils. LCDD most commonly involves kappa light chains (opposite to AL amyloidosis which is more commonly lambda). The nodular mesangial expansion on PAS mimics diabetic nodular glomerulosclerosis (Kimmelstiel-Wilson). Treatment targets the underlying clonal B-cell disorder with clone-directed chemotherapy.

Reference: Nasr et al 2012 – LCDD; KDIGO 2021 – MGRS Consensus; Leung et al 2019