Distinctive features and outcome-associated factors in generalized myasthenia gravis: A comparison of bulbar- and extremity-predominant subtypes

Abstract

Background: Risk factors for the conversion of ocular-onset myasthenia gravis (MG) to generalized MG (GMG) have been studied, but the characteristics of initially generalized onset MG subtypes remain unclear. This study aimed to identify distinguishing features of GMG by classifying patients into bulbar-predominant (GMG-B) and extremity-predominant (GMG-A) subgroups, and to evaluate prognostic factors associated with poor treatment response.

Methods: A retrospective analysis was conducted on patients between January 2009 and January 2024 who met predefined inclusion and exclusion criteria. Demographic, clinical, electrophysiological, laboratory, and treatment data were collected. Statistical analyses were performed to identify features of GMG subtype and markers of poor treatment response.

Results: A total of 118 patients were included (58 GMG-A, 60 GMG-B). GMG-B was associated with older age at onset, late-onset MG (>50 years), and male gender, whereas GMG-A was more common in early-onset MG (<50 years), female patients, and those with thymic pathology. MuSK antibody positivity strongly predicted poor treatment response, while AChR antibody positivity was associated with favorable outcomes.

Conclusion: This study is the first to examine distinctive features of GMG subtypes without preceding ocular symptoms and prognostic factors. Demographic variables (age at onset, onset category, and gender) and thymic pathology were significant predictors of GMG subtypes. Among laboratory markers, MuSK antibody positivity was the only independent predictor of poor treatment response.