Efficacy and safety of low-dose rituximab in MuSK antibody-positive myasthenia gravis: a single-center retrospective study.

BACKGROUND: Rituximab (RTX) is increasingly used for refractory myasthenia gravis (MG), particularly muscle-specific kinase antibody-positive MG (MuSK-MG). However, the optimal dosing regimen remains to be standardized, and conventional high-dose protocols may increase treatment burden, cumulative exposure, and infection-related concerns. This study evaluated the clinical efficacy, safety, and immunological effects of a low-dose RTX regimen in patients with MuSK-MG. METHODS: We retrospectively analyzed 35 patients with MuSK-MG who received low-dose RTX at the First Affiliated Hospital of Guangzhou University of Chinese Medicine between January 1, 2017 and August 1, 2025. RTX was administered as 100 mg on day 1 and 500 mg on day 2, and the regimen was repeated every 6 months. All patients received at least two treatment cycles. Clinical outcomes were assessed using Myasthenia Gravis Activities of Daily Living (MG-ADL) scores at baseline and at 3, 6, and 12 months after treatment. Secondary outcomes included Myasthenia Gravis Foundation of America post-intervention status (MGFA-PIS), adverse events, and peripheral CD19+ B-cell percentages in 24 patients. RESULTS: The mean baseline MG-ADL score was 9.5 ± 5.6 and decreased to 2.1 ± 2.3 at 3 months, 1.0 ± 1.8 at 6 months, and 0.5 ± 0.9 at 12 months (all p < 0.001 vs. baseline). At 3, 6, and 12 months, 21 (60.0%), 25 (71.4%), and 28 (80.0%) patients achieved minimal manifestation status (MMS) or better was 6 months, respectively. Kaplan-Meier analysis showed a median time to MMS or better of 6 months. Both the bulbar involvement (BI) and non-bulbar involvement (non-BI) subgroups showed significant clinical improvement, although the trajectories of MG-ADL improvement differed between subgroups. In the 24 patients with available immunological data, the median CD19+ B-cell percentage decreased from 12.6% before treatment to 0.30% at 6 months (p < 0.001). Adverse events were mild, and no serious infusion reactions, severe infections, or hepatic or renal dysfunction were observed. CONCLUSION: Low-dose RTX was associated with rapid and sustained clinical improvement and effective peripheral B-cell depletion in patients with MuSK-MG, with acceptable tolerability. These findings support low-dose RTX as a potential therapeutic option for MuSK-MG, although prospective multicenter studies with standardized dosing and longer follow-up are needed.