Factors Influencing the Conversion of Ocular Myasthenia Gravis to Generalized Myasthenia Gravis: A Retrospective Cohort Study

Purpose: The conversion rate of ocular myasthenia gravis (OMG) to generalized myasthenia gravis (GMG) lacks definitive predictors. Methods: This retrospective cohort study analyzed data collected at Siriraj Hospital between January 2007 and December 2019 to identify factors influencing OMG generalization and the time to conversion. The records of 200 OMG patients were reviewed and both acetylcholine receptor antibody (AChR Ab)-positive and AChR Ab-negative patients were included. Results: Seventy-eight (39%) developed GMG, with a median conversion time of 16 months (IQR 7.88, 33.75) and a 2-year conversion rate of 25.5%. AChR Ab positivity (adjusted HR 2.88, 95% CI 1.79-4.63), thymic abnormalities (adjusted HR 2.30, 95% CI 1.41-3.74), smoking (adjusted HR 1.78, 95% CI (1.04, 3.03), and pyridostigmine dosages > 180 mg/day (adjusted HR 2.33, 95% CI 1.41-3.87) were significantly associated with shorter conversion time. Conclusion: Thymic abnormalities and positive AChR Ab warrant routine assessment in all OMG patients. Smoking cessation is crucial, as it may impact conversion risk and time. Unlike previous findings suggesting a protective role of pyridostigmine, our data indicate a strong association between high-dose pyridostigmine and conversion to GMG, likely reflecting underlying disease severity. This underscores the need for individualized risk assessment in OMG management.