Kidney Injury in Multiple Myeloma: A Kidney Biopsy Teaching Case.

Myeloma-related kidney disease has several manifestations; the 2 most common histologic diagnoses are myeloma cast nephropathy and acute tubular necrosis. We describe a case of different kidney pathologies occurring concomitantly in a patient found to have immunoglobulin A κ multiple myeloma. A White woman in her 70s presented with an 8-month history of back pain and was found to have nephrotic-range proteinuria and acute kidney injury. Serum calcium level was 12.6 mg/dL. Kidney biopsy showed κ light chain only proliferative glomerulonephritis with monoclonal immunoglobulin deposits, crystalglobulinemia, light chain proximal tubulopathy with κ light chain deposits, mild tubular atrophy, and interstitial fibrosis. Free κ light chain ratio was >1,000 mg/dL and free κ light chain level was 4,670 mg/dL. Within a week following treatment of hypercalcemia and initiation of chemotherapy, her acute kidney injury and hypercalcemia resolved. This case highlights the many kidney manifestations of multiple myeloma and that prompt management targeting these manifestations, including hypercalcemia, can improve clinical outcomes.