Myeloma Cast Nephropathy and COVID-19: A Case Report of Multiple Myeloma Presenting as Acute Kidney Injury in the Setting of COVID-19

A 64-year-old African American male presented to the emergency department with subacute low back pain for two weeks and decreased urine output. He was found to have a potassium level of 9.2 mmol/L and was uremic with a creatinine level of 28.5 mg/dL and blood urea nitrogen (BUN) level of 201 mg/dL. He also tested positive for COVID-19. He was then started on continuous renal replacement therapy (CRRT). His urinalysis showed more than 500 mg/dL of protein. A workup for multiple myeloma was also conducted, and urine protein electrophoresis test was positive for free lambda light chains with a level of 17,700 mg/L and free kappa light chains with a level of 88.30 mg/L with a kappa:lambda free light chain ratio of 0.005. Additionally, serum Bence Jones protein level was elevated at 240 mg/dL, and serum beta-2 microglobulin level was elevated at 31.41 mg/L. An immunoglobulin (Ig) panel also showed low levels of IgG, IgA, and IgM. Kidney biopsy for this patient showed definite cast nephropathy and minimal chronic changes, with only one of over 20 glomeruli sclerosed and minimal interstitial deposits. The patient was started on chemotherapy with cyclophosphamide, bortezomib, and dexamethasone (CyBorD).