Different characteristics of nonthymomatous generalized myasthenia gravis with and without oropharyngeal involvement

Thymectomy represents a safe and valid approach for patients with myasthenia gravis. However, some factors may influence the efficacy of thymectomy. The objective of this study was to evaluate the clinical characteristics of generalized myasthenia gravis with oropharyngeal involvement and compare the postoperative outcome of generalized myasthenia gravis without and with oropharyngeal involvement.

From 1991 to 2002, there were 202 patients with nonthymomatous generalized myasthenia gravis (GMG), who underwent thymectomy by the transsternal approach or thoracoscopy. According to the clinical classification of the Myasthenia Gravis Foundation of America (MGFA), these patients have been subdivided into two groups: GMG without oropharyngeal involvement and GMG with oropharyngeal involvement. Complete stable remission, as defined by the MGFA Medical Task Force, was the primary endpoint for efficacy.

In all, 182 patients were followed up for at least 5 years. There were 135 cases of GMG without oropharyngeal involvement and 47 cases of GMG with oropharyngeal involvement. There were significant differences in postoperative pneumonia, ventilatory support time, and myasthenic crisis between patients with GMG with and without oropharyngeal involvement (p values were 0.040, 0.021, and 0.007, respectively). At 5 years of follow-up, the cumulative probability of reaching complete stable remission in GMG without oropharyngeal involvement was 18.5% at the end of the first year, and rose steadily in subsequent years (26.7%, 37.0%, 39.1%, and 40% at 2, 3, 4, and 5 years, respectively). In GMG with oropharyngeal involvement, it was 6.4%, 14.9%, 23.4%, 29.9%, and 31.9%, respectively, in the continual follow-up years. The first 3 years were associated with a significantly greater probability of achieving complete stable remission (p = 0.047 for the first year, p = 0.025 for the second one, and p = 0.048 for the third one). The later 2 years had no significant difference on complete stable remission.

Laryngeal myasthenia gravis is more severe and the prognosis after thymectomy is not as optimistic as for patients without oropharyngeal involvement.