Widespread crystalline inclusions affecting podocytes, tubular cells and interstitial histiocytes in the myeloma kidney.

Numerous crystalline inclusions were observed in glomerular and tubular epithelial cells in a 46-year-old female patient with multiple myeloma and renal dysfunction. On light microscopy, epithelial cells were filled with homogenous materials and were remarkably swollen. Infiltrations of histiocytes with expanded cytoplasm were also seen in the interstitium of the kidney and bone marrow. On electron microscopy, cytoplasmic inclusions had crystalline structure showing rhomboid and oval shapes. Immunofluorescence study revealed that these cells were positive for IgG-kappa. The combination chemotherapy followed by autologous stem cell transplantation led to a partial resolution of her renal dysfunction, continued by a slight reduction in the number of crystalline-containing podocytes at the second renal biopsy. Crystal inclusions in the kidney are rarely found and cause renal impairment in multiple myeloma.