Crystalloid deposits in the kidney

Light chain‐producing lymphoproliferative disorders such as multiple myeloma are frequently complicated by renal impairment. Typically, the renal biopsy of a patient with renal failure caused by multiple myeloma shows cast nephropathy, but occasionally crystals may be seen. We describe the case of a patient with acute renal failure caused by multiple myeloma in which, on renal and bone marrow biopsy, there were widespread crystalloid deposits. Crystalloid nephropathy is a very rare condition associated with multiple myeloma and other light chain‐secreting disorders. An underlying lymphoproliferative disorder should be considered in the differential diagnosis if crystalloid deposits are seen on a renal or other tissue biopsy.