Responsiveness to low-dose rituximab in refractory generalized myasthenia gravis

We aim to investigate the effect of a low dose of rituximab (RTX) in improving the clinical symptoms of refractory generalized myasthenia gravis (MG). Eight patients with refractory generalized MG were treated with a low dose of 600 mg RTX. Patients were evaluated by serial clinical scales, flow cytometry of peripheral blood B, T and NK cells, immunoglobulin, complement levels and antibody titer. The quantitative MG score (QMGS), manual muscle testing (MMT), MG-related activities of daily living (MG-ADL) and MG-specific quality-of-life (QOL) were recorded at baseline as well as 1, 3, and 6 months after RTX infusion. The initial improvement was recorded at 1 month after treatment. QMGS, MMT and MG-ADL were significantly improved and the average steroid dosage reduction was 43% (p = 0.018) at 6 months. 600 mg RTX was sufficient to deplete B cells and maintain low B-cell counts until 6 months after infusion. Treatment with RTX did not result in a significant change in the percentage of CD4+, CD8 T-cells while an average increase in the percentage of NK cells. Our study found successful B cell depletion was parallel to symptoms remission and change in serum C3 and C4 levels. Serum AChR antibody levels were independent of clinical response and not influenced by RTX. Therefore, low dose of 600 mg RTX may be sufficient in depleting B cells, maintaining low B-cell counts and improving the clinical symptoms of MG in 6 months.