Clinical outcome and predictive factors of irradiation-associated myasthenia gravis exacerbation in thymomatous patients

Exacerbations of myasthenia gravis (MG) in patients during radiotherapy for thymoma have never been adequately documented. This study aimed to identify potential risk factors for the occurrence of MG exacerbation during irradiation and to determine whether MG exacerbation during radiotherapy could affect the long-term clinical outcome of these patients. A total of 51 thymoma patients with MG receiving postoperative radiotherapy from January 2000 to March 2013 were retrospectively reviewed. Variables potentially affecting the occurrence of MG exacerbation were evaluated using Chi-square test or student’s t test. The difference in the chance of achieving complete stable remission (CSR), pharmacologic remission (PR), and general remission (GR) in the patients with and without MG exacerbation was determined by the log-rank test. Fifteen patients deteriorated during the irradiation. Univariate analysis showed that the MG duration between MG onset and irradiation was significantly longer in patients with MG exacerbation than patients without it (p = 0.029). The ratio of patients with a history of myasthenic crisis and bulbar symptoms were also higher in patients with exacerbation of MG than patients without exacerbation of MG, although it did not reach statistic significant. The log-rank test revealed that patients without MG exacerbation had higher PR and GR rates (p = 0.017 and p = 0.009, respectively). The worsening of symptoms appears to be related to the longer MG duration and more severe MG before irradiation. Moreover, the patients with MG exacerbation had a worse prognosis compared with patients without MG exacerbation. Our study highlights the need for preventing the occurrence of MG exacerbation in these patients.