IgA-kappa type multiple myeloma affecting proximal and distal renal tubules

A 45-year-old male was admitted because of chest pain, lumbago, and bilater al ankle pain. Examination disclosed hypophosphatemic osteomalacia, acquire d Fanconi syndrome, and abnormalities in distal nephron such as distal rena l tubular acidosis and renal diabetes insipidus. Further exploration reveal ed IgA kappa multiple myeloma excreting urinary Bence Jones protein (kappa- light chain). Renal biopsy revealed thick basement membranes and electron-d ense crystals in proximal tubular epithelial cells. Immunofluorescent studi es revealed deposition of kappa-light chain in renal tubular epithelial cel ls that caused the renal tubular damage. Although the osteomalacia was reli eved by medical treatment, the urinary Bence Jones protein and the renal tu bular defects were not improved by the chemotherapy for the myeloma. The pa tient died of exacerbation of multiple myeloma at 50 years of age.