Short-term and sustained clinical response following thymectomy in patients with myasthenia gravis

Background and purpose: This study was undertaken to investigate short- and long-term outcome following thymectomy in patients with acetylcholine receptor antibody (AChR-Ab)-positive myasthenia gravis (MG).

Methods: Rates of clinical response (defined as minimal manifestation, pharmacological remission, or complete stable remission) lasting for at least 1 year were retrospectively analyzed using Cox proportional hazard models. The occurrence of relapses was recorded during follow-up. Clinical factors associated with achieving an initial or a sustained response were analyzed.

Results: Ninety-four patients with a median age of 33 years (interquartile range [IQR] = 22-51), 68% with nonthymomatous MG and 32% with thymoma-associated MG, were included. An initial clinical response was reached in 72% (68/94). Neither sex, age at onset, thymus histology, delay to surgery after disease onset, surgical approach, corticosteroid treatment, nor clinical severity before thymectomy was significantly associated with achieving this endpoint. During long-term follow-up (median = 89.5 months, IQR = 46-189.5), only half of the patients with an initial response (34/68) had a sustained response without relapses. No clinical factors predicted whether the response would become sustained. In patients without immunosuppressive treatment before thymectomy (n = 24), a high AChR-Ab reduction rate after thymectomy was associated with a higher likelihood of achieving an initial response (p = 0.03).

Conclusions: Sustained long-term clinical response of MG patients after thymectomy is significantly lower than the initial response rates would suggest. The observation that none of the evaluated clinical factors was associated with a worse outcome supports the current clinical practice of patient selection for thymectomy. The relative decline of AChR-Abs after surgery appears to be a promising prognostic marker.