Active ectopic thymus predicts poor outcome after thymectomy in class III myasthenia gravis

Abstract

Objective: The presence of ectopic thymic tissue has been considered one of the most significant predictors of poor outcome after thymectomy for myasthenia gravis, but the role of active ectopic tissue is unknown. The current study analyzed the importance of this factor on post-thymectomy outcome of patients with class III myasthenia gravis.

Methods: We retrospectively reviewed 106 patients with class III, anti-acetylcholine receptor antibody-positive, nonthymomatous myasthenia gravis (70 female, 36 male; mean age, 41 ± 17 years) who underwent transsternal extended thymectomy between 1980 and 2005. Quality of life was assessed from 1996 with the Short Form 36 questionnaire. Prognosticators were investigated using complete stable remission and normalized component summaries as end points.

Results: Major morbidity rate was 5% with no perioperative mortality. Ectopic thymic tissue was detected in 51 patients (48%), 34 of whom (67%) presented germinal centers. Complete follow-up was available in 96 patients (mean 160 ± 91 months). Fifty-two patients (54%) achieved complete stable remission, and 20 patients (21%) presented clinical and pharmacologic improvement. Lack of postoperative improvement in physical and psychosocial domains was significantly correlated with active ectopic thymus. At Kaplan-Meier evaluation, duration of symptoms (>12 months) (P = .04), oropharyngeal involvement (P = .02), germinal centers (P = .03), ectopic thymus (P = .001), and active ectopic thymus (P < .0001) were negative predictors of complete stable remission. The presence of active ectopic thymus was the most significant negative predictor of complete stable remission at Cox regression (P = .03).

Conclusions: Extended thymectomy yields good outcome in patients with nonthymomatous class III myasthenia gravis. The presence of active ectopic thymus was the most significant predictor of poor outcome. These patients should be rigorously followed and undergo early aggressive therapy.