Factors influencing improvement and remission rates after thymectomy for myasthenia gravis.

BACKGROUND: Thymectomy has become an accepted option in the treatment of myasthenia gravis (MG). However, the optimal selection of patients for surgery remains controversial. OBJECTIVE: The objective of the study is to define factors influencing improvement and remission rates after thymectomy for MG. METHODS: We retrospectively reviewed our experience in the surgical management of patients with MG over the last 20 years, and analyzed if patient's age, sex, preoperative Osserman Stage, thymic histology, duration of symptoms, or radiological findings influenced outcome. RESULTS: There were 25 women and 10 men. Most of them presented with Osserman stage IIA (n = 12) and stage IIB (n = 17). Hyperplasia of the thymus was observed in 15 patients (43%), thymoma in 12 (34%), and atrophic or normal thymus in 8 (23%). Computed tomography (CT) had a positive predictive value of 91% in detecting thymoma and of 80% in detecting thymic hyperplasia. Over a mean follow-up of 96 months, MG improved markedly in 26 patients. Postoperative improvement was significantly greater in patients with advanced MG (stage IIB, III and IV), whereas a higher rate of remission occurred in patients with mild MG (stage I and IIA), and in those with thymic hyperplasia. No relation was observed between outcome and age, sex, duration of symptoms and abnormal CT findings. CONCLUSIONS: The beneficial effects of thymectomy are characterized by postoperative clinical improvement in most patients with moderate to severe preoperative myasthenic involvement and by a higher remission rate in patients with thymic hyperplasia and/or mild myasthenic symptoms.