Comparison of outcomes and postoperative immunotherapy between patients with non-thymomatous and thymomatous myasthenia gravis following thymectomy.

Background: Outcomes after thymectomy differ greatly between non-thymomatous and thymomatous myasthenia gravis (MG), meriting an in-depth exploration.

Objective: To examine the treatment and prognosis of non-thymomatous and thymomatous MG patients after thymectomy.

Design: A multicenter, retrospective, case-control study focused on MG patients following thymectomy from November 2010 to January 2024. After propensity score matching, 284 patients (142 with non-thymomatous MG and 142 with thymomatous MG) were included, with a median follow-up of 2.94 years.

Methods: Four outcomes were examined: minimal manifestations status (MMS) or better at the final visit, sustained clinical response, postoperative myasthenic crisis, and long-term mortality. Kaplan-Meier, logistic regression, cox regression, nomogram, receiver operating characteristic curve, decision curve, and calibration curve analyses were used for assessment.

Results: Non-thymoma patients had a lower proportion of postoperative myasthenic crisis (5.6% vs 13.4%, p = 0.026) and long-term mortality (1.4% vs 9.9%, p = 0.002) but a higher proportion of sustained clinical response (66.2% vs 52.1%, p = 0.016) than thymoma patients. For both non-thymomatous and thymomatous MG, anti-acetylcholine receptor antibody (AChR-Ab) positivity was the independent predictor for MMS or better at the final visit (p = 0.048; p = 0.016) and sustained clinical response (p = 0.035; p = 0.037). Most severe Myasthenia Gravis Foundation of America (MGFA) classification and high-grade Masaoka histopathology were independent predictors for postoperative myasthenic crisis (p < 0.001; p = 0.010) and long-term mortality (p = 0.006; p = 0.014) for thymomatous MG. Postoperative prednisone combined with tacrolimus (Pred + TAC) was associated with achieving sustained clinical response (p = 0.026; p = 0.030) and prednisone tapering for both groups.

Conclusion: Non-thymomatous MG exhibited a more benign course with better outcomes. AChR-Ab positivity indicated a better prognosis for both groups, while thymomatous MG with severe MGFA classification and high-grade histopathology requires close monitoring and follow-up. Postoperative Pred + TAC could be an effective immunotherapy option for beneficial outcomes.