Acetylcholine Receptor Antibody Positivity, RNST Abnormality, and Thymoma Predict Generalization in Ocular Myasthenia Gravis: A South Korean Cohort Study

Background: Ocular myasthenia gravis (OMG) can remain restricted to ocular symptoms or progress to generalized myasthenia gravis (GMG). However, the rate of generalization and its predictors may vary across populations, and data on South Korean patients remain inadequate. This study investigated the conversion rate from OMG to GMG and identified clinical, serologic, electrophysiologic, and thymic predictors of this generalization in a South Korean cohort. Methods: This retrospective cohort study included 89 patients who initially presented with OMG and were followed up for at least 2 years. The primary outcome was conversion to GMG during follow-up. The investigated predictors included demographic variables, initial ocular manifestations, acetylcholine receptor antibody (AChR-Ab) status and titer, repetitive nerve stimulation test (RNST) findings, thymic abnormalities, and immunosuppressive treatment. Kaplan–Meier analyses and Cox proportional-hazards models were used to evaluate the GMG-free survival rate and risk factors for conversion. Results: During follow-up, 10 patients (11.2%) progressed to GMG, with this conversion occurring within 2 years in 8 patients (9.0%). All converters were AChR-Ab positive. AChR-Ab positivity, RNST positivity, thymic abnormality, and thymoma were associated with GMG conversion in univariable analyses. RNST positivity in any tested muscle (hazard ratio [HR] = 12.66, 95% confidence interval [CI] = 2.68–59.76, p = 0.001) and thymoma (HR = 10.67, 95% CI = 3.06–37.27, p < 0.001) was associated with generalization. These associations persisted in the restricted multivariable Cox model. Conclusions: The rate of GMG conversion was relatively low in this South Korean OMG cohort, and most conversions occurred within 2 years. The presence of AChR-Ab positivity, RNST abnormality, or thymoma may characterize high-risk patients who require closer monitoring during the early disease course.