Thymoma hyalinized by steroid therapy in myasthenia gravis.

We encountered a 72-year-old woman with myasthenia gravis and thymoma who received glucocorticoid therapy for respiratory failure before undergoing thymectomy. After the antiacetylcholine receptor antibody titer was normalized, and the thymoma shrunk with prednisolone, the patient was free from symptoms. On pathological examination, the majority of the thymoma (type B2) had been hyalinized. Preoperative steroid therapy was effective in stabilizing myasthenia gravis and in inducing apoptosis of both epithelial and lymphocytic components of the thymoma.