Changes in Demographic and Clinical Characteristics of MuSK Myasthenia Gravis

BACKGROUND: Over the last two decades, an increasing number of late- and very-late onset myasthenia gravis cases (VLOMG) with acetylcholine receptor antibodies (AChR-MG) have been reported, whereas demographic studies on muscle-specific tyrosine kinase antibodies MG (MuSK-MG) are lacking. We investigated whether the proportion of patients with MuSK-MG with onset ≥ 50 years has increased and whether these patients show distinct clinical characteristics. METHODS: We retrospectively enrolled consecutive patients with MuSK-MG onset ≥ 16 years followed between 1980 and 2025 at our tertiary center. Demographic characteristics and maximum disease severity, classified according to Myasthenia Gravis Foundation of America classification, were analyzed. Patients were stratified into three age-at-onset subgroups. RESULTS: Overall, 120 patients were included. A significant increase in the median age at MuSK-MG onset was observed, from 36 years (IQR, 23-45.75) in the 1980s to 47 years (IQR, 29-69) in the 2013-2025 period (p = 0.033). Patients with onset ≥ 50 years increased from 2/17 (11.8%) to 19/39 (48.7%) (p = 0.015), including 12 VLOMG cases. Males increased from 23.5% to 35.9%. Maximum MG severity decreased over time, with a remarkable reduction of respiratory crises (p = 0.004), with no significant differences across age-at-onset groups. CONCLUSIONS: Demographic changes observed in AChR-MG also occur, though less prominently, in MuSK-MG.