Clinical Characteristics of Thymic Tumor-associated Myasthenia Gravis

ABSTRACT

BACKGROUND & PURPOSE: Thymic tumors are frequently found in patients with myasthenia gravis(MG); the patients with thymoma seem to be more associated with severe MG. This study was performed to analyse the clinical characteristics of thymic tumor-associated MGs and to compare the patients with invasive and noninvasive thymomas. METHODS: We retrospectively reviewed the medical records of 305 MG subjects(MF = 112193, age = 30.4 ? 8.1 years) who had been diagnosed to have MG from January 1986 to June 1996, and analysed the clinical characteristics of MG subjects with thymic tumors. Forty seven patients were confirmed to have thymic tumor by the postoperative histopathologic findings(thymic tumor(TT) group) and 191 were known to have nonneoplastic thymus by chest CT or postoperative histopathologic findings(nonneoplastic thymus(NN) group). RESULTS: The incidence of thymic tumor-associated MG was 25.2%. The male to female ratio for the TT and the NN groups were 11 and 12, and the mean age of onset were 42.9 ? 11.2 years and 28.3 ? 17.5 years, respectively. When we evaluated the disease severity by Osserman's classification, 85% of the TT group and 51% of NN group were severely affected(Iib, III, IV). The generalization of symptoms occurred in 98% of the TT group and 66% of the NN group. The disease severity and the clinical outcome were not significantly different between the MGs with invasive thymoma, noninvasive thymoma and thymic carcinoma. CONCLUSION: Compared with those of MGs with nonneoplastic thymus, the thymic tumor-associated MGs showed several different clinical phenotypes, as in the followings; they showed no sex predominance, the onset age was older, more common generalization of myasthenic symptoms, and more patients were severely affected. The severity and outcome were not different between the MGs with thymic tumor.