Ultrastructural identification of a proximal tubulopathy without crystals in a relapsed multiple myeloma patient

A multiple myeloma patient, who had been treated with a hematopoietic stem cell transplant, underwent a renal biopsy for investigation of a possible relapse of disease as indicated by increased serum creatinine and positive urinary Bence-Jones protein containing increased kappa light chain. Paraprotein-related renal disease was not evident by light microscopy or immunofluorescence microscopy however electron microscopy demonstrated a proximal tubulopathy with intracytoplasmic non-crystalline inclusions. The ultrastructural findings suggested possible end-organ involvement by the disease and follow-up studies subsequently revealed a relapsed multiple myeloma in the patient. The case exemplifies the usefulness of electron microscopy in detecting paraproteins that, in some instances, may be difficult to demonstrate by other techniques.