Outcomes in Relation to the Age at Onset in Patients With Myasthenia Gravis

Patients with myasthenia gravis (MG) exhibit significant heterogeneity based on age at disease onset. However, existing retrospective studies in China remain confined to single-center settings with limitations in sample size adequacy. The aim of this study was to compare clinical characteristics, treatment responsiveness, and long-term postintervention status of patients with MG across different onset ages.

This was an observational, cross-sectional, multicenter, retrospective study. We reviewed the medical records of patients diagnosed with MG who were hospitalized in 3 MG centers of China from January 2012 to December 2022. Demographic information, clinical characteristics, and therapeutic data were extracted from the electronic medical record system, and responsiveness to treatment was followed up. Patients were classified into 3 age subgroups: juvenile MG (age at onset <18 years), early-onset MG (onset ≥18 and <50 years), and late-onset MG (onset ≥50 years). Time to minimal manifestation (MM) or better status was assessed using Kaplan-Meier curves and Cox proportional hazards regression models.

Among 2,574 patients with MG meeting inclusion criteria, 1,023 (39.7%) had juvenile MG, 568 (22.1%) had early-onset MG, and 983 (38.2%) had late-onset MG. Juvenile MG showed a peak onset at 0-4 years (61.9%), predominantly affecting female individuals (58.3%) and presenting mainly with ocular symptoms (90.2%). While most juvenile patients responded well to treatment, pubertal onset (OR 5.2 [95% CI 2.75-9.98]), thymic hyperplasia (OR 11.4 [95% CI 5.64-22.99]), and positive acetylcholine receptor antibodies (OR 3.1 [95% CI 1.65-5.65]) were risk factors of secondary generalization. In adults, late-onset MG was more common than early-onset MG, with male predominance (53.0%) and greater comorbidity burden (40.6%), including hypertension, diabetes mellitus, and coronary heart disease. The proportion of patients with late-onset MG (66.7%) achieving MM or better status was lower than that of patients with early-onset MG (74.7%) (p < 0.001). Multivariable analysis identified late-onset MG (HR 0.8 [95% CI 0.69-0.91]), thymic abnormalities (HR 0.8 [95% CI 0.67-0.91]; HR 0.7 [95% CI 0.61-0.88]), and generalized MG (HR 0.8 [95% CI 0.71-0.96]) as factors associated with poorer outcomes.

This large cohort study highlights distinct clinical and prognostic differences in MG by age at onset. Pubertal-onset juvenile MG and late-onset MG represent vulnerable groups, with late-onset MG demonstrating poorer prognosis.