Acute renal failure in multiple myeloma is most frequently caused by cast nephropathy, when excess monoclonal free light chains co-precipitate with Tamm-Horsfall protein in the distal nephron, causing tubular obstruction. The natural history of cast nephropathy after diagnosis is unknown. This report provides supporting histological evidence that, as serum free light chain concentrations fall, intratubular casts may resolve within weeks.

We report the case of a 61-year-old Caucasian woman who presented with multiple myeloma and dialysis-dependent acute renal failure, with serum kappa free light chain concentrations of 15,700 mg/litre (normal range 3.3 to 19.4 mg/litre). Renal biopsy demonstrated cast nephropathy with waxy casts in distal tubules and collecting ducts. There was an interstitial inflammatory cell infiltrate with diffuse fibrosis and tubular atrophy. Following rehydration, chemotherapy and free light chain removal using high cut-off haemodialysis, free light chain concentrations fell to less than 5% of the starting level (500 mg/litre). A repeat renal biopsy 6 weeks after the first showed resolution of cast nephropathy.

These observations indicate that cast nephropathy can quickly resolve on rapid reduction of monoclonal serum free light chains. This has important implications for the development of treatment strategies aimed at improving renal recovery rates for patients in this setting.