Coexistence of myeloma cast nephropathy, light chain deposition disease, and nonamyloid fibrils in a patient with multiple myeloma.

Plasma cell dyscrasias can present as myeloma cast nephropathy, AL amyloid, or light chain deposition disease. We describe the unusual kidney biopsy findings of concurrent myeloma cast nephropathy and glomerular nonamyloid fibrillary deposits composed of immunoglobulin G (IgG) heavy chains and λ light chains in a patient with multiple myeloma who presented with acute renal failure. We performed laser microdissection and mass spectrometry-based proteomic analysis, which showed that the fibrillary deposits likely contained Igγ1 constant region and λ light chain constant region, whereas κ light chains and serum amyloid P proteins were absent. Treatment of multiple myeloma resulted in resolution of the renal manifestations, suggesting a common underlying mechanism for the cast nephropathy and heavy and light chain deposition disease. We show that laser microdissection and mass spectrometry is an extremely useful ancillary test for the diagnosis of heavy and light chain deposition diseases.