To characterize how the relapse-prevention effect of maintenance therapy changes over time in MOGAD.

Myelin oligodendrocyte glycoprotein antibody–associated disease (MOGAD) often relapses. Preventing further attacks is central to care, but the timing and durability of benefit from maintenance therapy, and whether antibody titer modifies this effect, remain uncertain.

We performed a retrospective cohort study using an institutional database of patients with MOGAD at Mass General Brigham in Boston. Relapse risk was modeled with piecewise exponential additive mixed models. Nonsteroidal maintenance therapy (rituximab, intravenous immunoglobulin, mycophenolate mofetil) was represented with smooth functions of time-since-treatment-start after a 30-day grace period and time-since-disease-onset, with clinical covariate adjustment. Hazard ratio (HR) curves for therapy versus off-therapy were obtained by averaging model-based hazards. Analyses were repeated by binary MOG IgG titer (≥1:1000 vs <1:1000).

We included 154 patients with at least two MOG IgG titer measurements during follow-up. Maintenance therapy was associated with an early reduction in relapse hazard after initiation, most evident when started within approximately 2 years after onset. Evaluated two years after treatment start, estimated HRs for relapse (therapy vs off-therapy) were 0.15 (95% CI, 0.03–0.67) when therapy began 0.5 years after disease onset, 0.22 (95% CI, 0.07–0.73) when started at 2 years, and 0.36 (95% CI, 0.10–1.21) when started at 3 years. Initiation beyond this window showed little additional reduction in relapse risk. The time-varying effects were broadly similar across higher and lower MOG titers.

In MOGAD, relapse-prevention benefits of maintenance therapy appear greatest when started earlier in the disease course and wane over time. These estimates may help guide initiation and de-escalation decisions.