An 85-year-old gentleman presents to the clinic with nephrotic range proteinuria and a creatinine of 10.0 mg/dl. He reports a 20 lb weight loss over the last 2 months and says that he is having trouble keeping down anything solid. A SPEP and UPEP show a monoclonal kappa band.
What is the best diagnosis?
a. Light Chain Cast Nephropathy
b. Light Chain Deposition Disease
c. Light Chain Tubulopathy
d. AL-Type Amyloidosis
The correct answer is a (light chain cast nephropathy).
The biopsy shows several fractured casts with a cell reaction. The casts are PAS-negative and “chatter” marks are identified. The brighter staining for kappa as compared to lambda within the casts confirms the presence of a light chain cast nephropathy. Light chain deposition disease is a paraproteinemia which involves deposition of light chains within the glomerular and tubular basement membranes. It is true that there would be restriction in this case, but the biopsy shows the presence of casts. Light chain tubulopathy is a paraproteinemia which involves crystal and crystalloid-like structures within the tubules which show kappa or lambda restriction. AL-type amyloidosis involves deposition of a Congo-red positive eosinophilic material within the kidney.
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