Postthymectomy myasthenia gravis: relationship with thymoma and antiacetylcholine receptor antibody.

BACKGROUND: Myasthenia gravis occasionally develops in a postthymectomy patient with no preoperative history of this disease.

METHODS: We retrospectively assessed the clinical course, history, and findings of myasthenia gravis, and examined the serum titers of antiacetylcholine receptor-binding antibody in patients who had undergone thymectomy.

RESULTS: We enrolled 67 patients with thymoma and 11 with other thymic tumors, all of whom underwent thymectomy. Twelve thymoma patients had had myasthenia gravis preoperatively, and their serum titers were all positive for antiacetylcholine receptor-binding antibody. Thirteen of 55 patients (24%) who had had no preoperative myasthenia gravis, but none with other thymic tumors (p < 0.0001), had a similar positive reaction. Five of the 55 thymoma patients without preoperative myasthenia gravis presented with the disease 3 to 46 months after thymectomy. These 5 patients showed no significant clinical or pathologic features, and in only 1 did the tumor recur. However, they all, including 2 patients who had shown negative antiacetylcholine receptor-binding antibody titers preoperatively, showed the presence of antiacetylcholine receptor antibody after onset. No postoperative elevation of the antiacetylcholine receptor binding antibody titer was observed in any postthymectomy patient who had no myasthenia gravis.

CONCLUSIONS: We found that patients in whom postthymectomy myasthenia gravis developed showed high titers of antiacetylcholine receptor-binding antibody at the onset of the myasthenia gravis. We suggest that a positive preoperative antiacetylcholine receptor antibody level may be a risk factor for postthymectomy myasthenia gravis.