A 67-year-old man has fatigue, bone pain, and a creatinine of 5.8 mg/dL. Serum calcium is 11.8 mg/dL, haemoglobin 8.9 g/dL, and urine dipstick for protein is trace despite a 24-hour urine protein of 3.9 g/day. Urinalysis is otherwise bland. What is the MOST likely cause of his kidney failure?
- A Membranous nephropathy with heavy albuminuria
- B Cast nephropathy from filtered monoclonal free light chains ✓
- C Amyloidosis with AL deposits confined to the glomeruli
- D Hypercalcaemic nephrogenic diabetes insipidus alone
Correct answer: B. Cast nephropathy from filtered monoclonal free light chains
Explanation
Myeloma cast nephropathy occurs when filtered monoclonal light chains form obstructing casts with Tamm-Horsfall protein in distal tubules. Because standard dipsticks detect albumin and not free light chains, the discordance between a trace dipstick and substantial 24-hour protein is the classic clue. Hypercalcaemia aggravates renal vasoconstriction and dehydration here, but the magnitude of renal failure with this protein pattern points to cast nephropathy.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.