Environmental factors affecting the risk of generalization for ocular-onset myasthenia gravis: a nationwide cohort study

Background: The environmental effects on the prognosis of ocular myasthenia gravis (OMG) remain largely unexplored.Aim: To investigate the association between specific environmental factors and the generalization of OMG.Design: The cohort study was conducted in China based on a nationwide multicenter database.Methods: Adult patients with OMG at onset, who were followed up for at least 2 years until May 2022, were included. We collected data on demographic and clinical factors, as well as environmental factors, including latitude, socioeconomic status (per capita disposable income [PDI] at provincial level and education) and smoking. The study outcome was the time to the development of generalized myasthenia gravis (GMG). Cox models were employed to examine the association between environmental exposures and generalization. Restricted cubic spline was used to model the association of latitude with generalization risk.Results: A total of 1396 participants were included. During a median follow-up of 5.15 (interquartile range [IQR] 3.37-9.03) years, 735 patients developed GMG within a median of 5.69 (IQR 1.10-15.66) years. Latitude of 20-50(degrees)N showed a U-shaped relation with generalization risk, with the lowest risk at around 30(degrees)N; both higher and lower latitudes were associated with the increased risk (P for non-linearity <0.001). Living in areas with lower PDI had 1.28-2.11 times higher risk of generalization. No significant association was observed with education or smoking.Conclusions: Latitude and provincial-level PDI were associated with the generalization of OMG in China. Further studies are warranted to validate our findings and investigate their potential applications in clinical practice and health policy.