OBJECTIVETo evaluate the different pathological and clinical characteristics of thymomas with and without myasthenia gravis (MG) and to determine whether the presence of MG influences the prognosis in thymoma patients.

METHODSThe clinical data from 228 consecutive patients (median sternotomy were used in 153, video-assisted thoracoscopic themectomy were used in 75) operated on from January 1992 to December 2007 was analyzed retrospectively. These thymoma patients had been subdivided into two groups: thymoma with MG (n = 125) and thymoma without MG (n = 103). All thymic epithelial tumors were classified according to the WHO histologic classification and the Masaoka clinical staging system. The result was evaluated according to the Myasthenia Gravis Foundation of America's criterion. The clinical features of the 2 test was compared between the two groups by χ² test, and the survival were compared between the two groups by Cox analysis.

RESULTSThere were no peri-operative deaths. 19 cases were inoperable (6 in the group with MG, 13 without MG (χ² = 4.52, P = 0.035)). The proportions of type A and thymic carcinoma were 0 in the group with MG, 10.5% (11/103) and 11.6% (12/103) respectively in the group without MG. According to the Masaoka's clinical staging, in the group MG, 24.8% (31/125) patients were stage III and IV; in the group without MG, 33.0% (34/103) patients were stage III and IV. There was a significant difference between hyperplastic paraneoplastic thymus coexisting in 28.8% (36/125) patients with MG and only 5.8% (6/103) in patients without MG (χ² = 20.91, P = 0.000) Microthymoma was identified in the paraneoplastic thymus of 3 patients with MG. There were 198 patients followed up, the rate was 86.8% (198/228). There was no recurrence in patients with type A and a few patients with type AB, B1, B2, B3 thymoma and thymic carcinoma recurred. The actuarial 5- and 10-year survival rates were 89.3% and 81.2% for patients with MG respectively, and 90.0% and 78.9% for patients without MG respectively. Within 5 years postoperatively, 6 of 9 patients with MG died of myasthenia crisis, while 6 out of 7 deaths in patients without MG were attributable to inoperable tumors (stage IV) and thymic carcinoma.

CONCLUSIONSThe existence of myasthenia gravis has little influence on the prognosis of thymomas, but it is good for early diagnosis and treatment. Extended thymectomy should be performed to all patients with thymoma, no matter they have myasthenia gravis or not. The main cause of death is myasthenia crisis for thymoma patients with MG and stage IV and (or) thymic carcinoma for patients without MG.