The curious case of light chain cast nephropathy in a renal allograft recipient

Myeloma cast nephropathy in renal allograft recipients without pre-transplant diagnosis of multiple myeloma is rare. A 32-year-old hypertensive male presented to our institute as a prospective renal allograft recipient. Hemoglobin was 10.1 mg/dl. He did not have hypercalcemia, and the albumin/globulin ratio was 1.33. Urinalysis did not show any proteinuria or active sediments. Ultrasonography of the abdomen showed bilateral contracted kidneys. He underwent an uneventful renal transplant surgery and had immediate graft function. After 1 month, he tested positive for severe acute respiratory syndrome coronavirus 2 and developed graft dysfunction. Graft biopsy showed features of myeloma cast nephropathy. He had elevated lambda chains with an involved-to-uninvolved free light chain ratio of >100. Serum immunofixation electrophoresis showed a monoclonal band in the lambda region. Bone marrow biopsy showed plasmacytosis with 18.6% immature plasma cells. He improved on cyclophosphamide, bortezomib, and dexamethasone regimens.