Thymectomy outcomes in myasthenia gravis: comparative analysis between treatment before and after five years

Abstract

Background: Thymectomy is one of the standard treatments for myasthenia gravis (MG) with positive anti-acetylcholine receptor antibody. It is primarily validated and performed early in the natural history of the disease. This study aimed to evaluate the benefits of thymectomy performed five years later of MG and the impact of remission or minimal symptoms. Objective: To demonstrate that thymectomy performed after 5 years of disease can be beneficial and still considered as a treatment option, especially in the Brazilian Public Health System, with scarce treatment options. Methods: Analysis of data from medical records at a tertiary care center in Neuromuscular Diseases at the Hospital das Clínicas de São Paulo. A comparative clinical evaluation was performed using the MG-ADL and MG-Composite scales between the pre-surgery attendance and the last clinical evaluation. Results: Data from 188 patients with myasthenia gravis treated with thymectomy were analyzed. 83 patients were tested and were positive for anti-Ach antibody. Patients treated with thymectomy, approximately 22% (43) underwent thymectomy after 5 years of diagnosis, with an average of 11 years between diagnosis and surgery. About 77% of patients underwent thymectomy within 5 years of MG, with 72% achieving disease remission after 1 to 2 years. The mean MG-ADL scale score at the last assessment of patients with thymectomy >5 years was 2.72 points and mean MG Composite scale score was 4.24 points. Clinical remission or minimal disease symptoms occurred in 51% of patients treated after 5 years. Conclusion: The MGTX study and its extension confirm the benefit of thymectomy performed up to 5 years of MG presentation. Cohorts and observational series have shown that a longer time between the onset of MG and thymectomy is associated with worse outcomes (lower chance of remission, slower response), with a longer preoperative duration predicting delayed or absent response. Our observational study of retrospective and prospective data showed that approximately half of patients experienced disease recurrence and symptom improvement according to clinical scales with delayed thymectomy, at a relatively high mean time of over 10 years. In a recent meta-analysis of patients with late-onset non-thymomatous MG (LOMG – onset after 50yo), thymectomy after 5 years has been shown to have less or no benefit compared to conservative treatment. Therefore, further studies and evaluations of thymectomy in patients with longer duration of neuromuscular disease should be conducted, with the aim of adding this long-term treatment to the list of treatments for myasthenia gravis.