Baseline high disease activity and short-term response to efgartigimod in AChR-positive generalized myasthenia gravis: a single-center registry-based cohort study

Myasthenia gravis disease activity has been proposed as a clinically relevant framework for identifying patients who may require treatment escalation. However, whether baseline high disease activity (HDA), as a category within this framework, influences response to neonatal Fc receptor (FcRn) antagonism remains unclear. We conducted a registry-based retrospective cohort study of adults with acetylcholine receptor antibody-positive generalized myasthenia gravis (AChR-Ab+ gMG) who completed one cycle of intravenous efgartigimod (10 mg/kg weekly for 4 weeks). Patients were classified into HDA and mild-to-moderate disease activity (M/MDA) groups using criteria based on the 2023 German MG guideline and adapted to the Chinese MG registry setting. The primary outcomes were minimal symptom expression (MSE) and clinically meaningful improvement (CMI) at week 4, compared between disease activity groups. Logistic regression was used to evaluate factors associated with MSE. A total of 93 patients were included, with 62 classified as HDA and 31 as M/MDA. At week 4, MSE was achieved by 60 patients (64.5%) and CMI by 89 patients (95.7%). No statistically significant between-group difference was observed for MSE or CMI. In multivariable analysis, baseline Myasthenia Gravis Activities of Daily Living (MG-ADL) score was associated with MSE (OR = 0.85, 95% CI: 0.73–0.99, p = 0.04), whereas disease activity category was not. In patients with available 12-week follow-up, no significant group-by-time interaction in MG-ADL change was detected. One serious adverse event was reported; no other serious adverse events and no new short-term safety signals were identified. No statistically significant association was detected between baseline HDA and short-term response in this cohort. The findings do not establish equivalence, and longer-term durability requires prospective multicenter evaluation.