A Case of Cast Nephropathy Found as the Cause of Severe Renal Failure.

Cast nephropathy is rare kidney disease with slow progression. It is associated with multiple myeloma (MM). In this study, we report a case of cast nephropathy in an 86-year-old woman who was previously independent in her activities of daily living (ADLs). However, she was found to have severe renal impairment after vomiting and a decrease in her ADLs. Blood and urine tests revealed the renal disorder. The patient was immediately treated with hemodiafiltration. IgG, IgA, and IgM levels were decreased by immunoelectrophoresis. A kidney biopsy showed crystals and periodic acid-Schiff stain (PAS)-negative urinary casts in the tubules. Bence Jones protein-lambda type M protein was detected in the urine. The patient was diagnosed with cast nephropathy due to MM. Hemodialysis was continued. The patient's family and the patient did not wish to initiate chemotherapy. The decision was made to follow the patient's progress. In this case, a patient who was originally independent in her ADLs developed severe renal failure with an acute course. This case suggests the importance of differentiating MM based on renal failure, even if the presentation is not typical, as elderly patients may have an atypical presentation of the disease, which can avoid invasive procedures such as renal biopsy.