Renal biopsy diagnosis of clinically silent multiple myeloma.

Acute renal failure due to multiple myeloma is uncommon but may be the presenting feature of the disease. When it occurs, the underlying multiple myeloma is usually easily diagnosed by the presence of a serum M protein, hypercalcemia, skeletal pain, or typical bone lesions. We report here four cases of patients who, at the time they developed acute renal failure, had none of these findings nor any other historical or physical evidence of multiple myeloma. A renal biopsy in all four cases revealed the typical diagnostic features of "myeloma kidney" and led to confirmation of the diagnosis by bone marrow examination. Tamm-Horsfall protein was identified within myeloma casts and the glomerular urinary space, suggesting that tubular obstruction and retrograde urine flow precedes the development of "myeloma kidney" and acute renal failure.