Myasthenia gravis with thymic epithelial tumour: a retrospective analysis of a Japanese database

Objectives: Myasthenia gravis (MG) has been reported to correlate with earlier stage and Type B thymomas by the World Health Organization classification. We analysed a large database of clinical characteristics of patients with MG and thymic epithelial tumours to elucidate whether the severity of MG affected postoperative survival of those with thymic epithelial neoplasms.

Methods: We conducted a multi-institutional study on the patients who had undergone surgical treatment for thymic epithelial tumours between 1991 and 2010. We examined Masaoka stage, pathological type, serum titre of antiacetylcholine receptor antigen, severity of MG and postoperative prognosis of the patients with or without MG.

Results: Of the 2835 registered patients at 32 institutes belonging to the Japanese Association for Research on the Thymus, 2638 were eligible for the study. MG was present in 598 patients (23%). Patients with MG had thymic epithelial tumours with significantly earlier stage (P = 0.0082) and significantly smaller tumours (P = 0.000) than those without. Type A, Type AB thymomas and thymic carcinomas were less frequently observed in patients with MG. Three of 304 patients (1%) with thymic carcinomas had MG preoperatively. Serum titres of antiacetylcholine receptor antibodies were positive in 98% of patients with MG, and 23% of those without. Patients with generalized MG had significantly higher titres of antiacetylcholine receptor antibodies than those with ocular MG (P = 0.000). The postoperative 30-day mortality rate was 0.3%. Postoperative 5- and 10-year survival rates of thymoma patients with MG and those without MG were 94 and 96, and 89 and 89%, respectively. We found no statistical difference in the postoperative survival rate or recurrence-free rate between the two groups. We found no significant statistical differences of these rates by MGFA classification or surgical approach.

Conclusions: We conclude that earlier stage, smaller size or Type B thymomas are more frequently associated with MG, and MG may have no impact on the overall survival of patients with thymoma. We suggest that postoperative survival time of the patients with MG and thymic epithelial tumours may be mainly affected by the tumours, not by MG.