Tubular proteinuria during treatment with cyclosporin A--a case report.

A patient with relapsing polychondritis developed a progressive destruction of tracheal cartilage despite treatment with immunosuppressive and cytotoxic agents. Cyclosporin A therapy was instituted and has been continued for more than two years, concomitant with a steady improvement and remission of the disease. During the treatment period an increased urinary excretion of beta 2-microglobulin was measured, indicating renal tubular damage. The tubular proteinuria preceded an elevation of serum creatinine and a drop in creatinine-clearance. Thus, beta 2-microglobulin might be a sensitive indicator of nephrotoxicity and of value for the evaluation of the long-term side effects of Cyclosporin A particularly in patients with extrarenal disease.