[A post-thymomectomy case of myasthenia gravis which developed nephrotic syndrome with membranous nephropathy during azathioprine administration].

We report a 46-year-old woman who has been suffered from myasthenia gravis and underwent thymomectomy in December 1988. Her myasthenic symptoms improved by treatment with corticosteroid and azathioprine; the latter drug was administrated for more than one year. She noticed weight gain of 10 kg and edema in both legs and feet, which developed acutely in August 1994. Laboratory data showed that she suffered from nephrotic syndrome with a large amount of proteinuria (15 g/day). Renal biopsy revealed that biopsied glomeruli showed early stage of membranous nephropathy associated with acute tubular necrosis. Although therapeutic trials of steroid pulses could not eliminate proteinuria, substitution of cyclophosphamide for azathioprine brought marked improvement of the nephrotic syndrome with disappearance of the urinary protein excretion within 10 days. From reports of similar cases with myasthenia gravis in Japan and in Europe, therapeutic usage of azathioprine in patients with myasthenia gravis associated with thymoma should be cautious for appearance of nephrotic syndrome when azathioprine is continued for more than one year.