A 70-year-old man with multiple myeloma has urinary Bence-Jones protein. The principal mechanism of 'myeloma kidney' (cast nephropathy) is:

• A Monoclonal IgG deposits in glomerular mesangium activating complement
• B Hyperuricemia causing urate crystals in collecting ducts
• C Hypercalcemia-induced nephrocalcinosis of the cortex
• D Free light chains precipitating with Tamm-Horsfall protein in distal tubules forming obstructive casts ✓

Explanation

Myeloma kidney (cast nephropathy) results from filtered free light chains binding Tamm-Horsfall (uromodulin) protein in the distal tubule and collecting duct, forming large obstructive laminated casts surrounded by giant cells. This is distinct from light-chain deposition disease (mesangial deposits) or AL amyloidosis. Hyperuricemia and hypercalcemia can also injure kidneys in myeloma but are not the principal mechanism of cast nephropathy.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.