Effects of preoperative duration of symptoms on patients with myasthenia gravis.

In 80 patients with type II nonthymomatous myasthenia gravis who underwent extended thymectomy, we investigated preoperative duration of symptoms, prognosis after thymectomy, immunological findings, and germinal center formation in the thymus. Our findings included the following. First, the palliation rate after thymectomy ranged from 73 to 100% and was independent of the preoperative duration of symptoms. The remission rate was high in patients with a short preoperative duration. Second, the lymphocyte count of peripheral blood decreased as preoperative duration increased. Third, the percentage of positive reactions to purified protein derivative of tuberculin decreased as preoperative duration increased: 100% in the one-year group, 78% in the two-year group, 75% in the three-year group, and 56% in the four-year group. Fourth, the degree of germinal center formation in the thymus was higher in patients with a longer preoperative duration. The correlation between germinal center formation and preoperative duration was significant. Finally, the T-cell population in peripheral blood and immunoglobulin, and antibody to acetylcholine receptor in serum, had no significant relationship with the preoperative duration of myasthenia gravis.