Background: Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junction of skeletal muscles. Main treatments consist of pharmacologic and surgical treatments, such as a thymectomy. Even when patients receive recommended therapy, many still suffer from weaknesses. There is very limited data available regarding clinical responses to treatment and longterm outcomes of MG.

Objective: To study the long-term outcomes of clinical responses after thymectomies in patients with MG, as well as compare dosages of medication use before and after thymectomy and associating factors.

Materials and Methods: Retrospectively reviewed 123 MG patients treated by pharmacological treatment and thymectomy between 1997 and 2011 in Srinagarind Hospital, Khon Kaen University. Endpoints included improvement of clinical symptoms during follow-up time and the response to therapy-defined categories such as complete stable remission (CSR), pharmacologic remission (PR), improved, stabilized or worsened. The average dosage of pharmacological treatment before and after the procedure and factors associated with satisfactory outcomes are also studied.

Results: Among 123 patients, 94(75.8%) are females with a median age of 49.82 years (IQR 41.76 to 58.36) and average age of diagnosis of 37.45 years (27.51 to 45.33). The average period for thymectomy after diagnosis was 8.12 months (1.87 to 23.21). The surgical method of thymectomy is divided into transsternal and video-assisted thoracoscopic thymectomy, each with 115 and 8 patients respectively. The duration of follow-up was 36.18 months (19.82 to 76.9). Histological examination showed thymoma and non-thymoma were 20.32% and 79.68% respectively. In terms of overall response, 95.12% had a good response (CSR, PR, improved), while 4.88% had a poor response (stable, worse). 28 patients (22.76%) had CSR, 70 patients (56.91%) had PR and 19 patients (15.45%) had improvement of clinical symptoms. The disease had stabilized in 5 patients (4.07%), and 1 patient (0.81%) had worsening symptoms. Most of the patients required lower doses of pyridostigmine and prednisolone after surgery. Multivariate
Cox regression analysis revealed that those with an age of diagnosis before 40 years old and lower dose of pyridostigmine use at 12 months after thymectomy showed significantly higher rates of CSR.

Conclusion: Thymectomy along with pharmacologic therapy for MG patients showed satisfactory results in achieving remission
and improving clinical response rates. Favorable factors for satisfactory outcome were age of diagnosis before 40 years old and lower dose of pyridostigmine use at 12 months after thymectomy.

Keywords: Myasthenia gravis, Thymectomy, Outcome