Differential response to rituximab in anti-AChR and anti-MuSK positive myasthenia gravis patients: a single-center retrospective study.

BACKGROUND

B-cell targeted therapy with rituximab has shown durable response in treating refractory myasthenia gravis (MG). This study compares the response to rituximab between patients with acetylcholine receptor autoantibody positive (AChR+) and muscle-specific kinase autoantibody positive (MuSK+) MG.

METHODS

This retrospective study included 33 patients with either AChR+ or MuSK+ MG who were treated with rituximab from 05/31/2003 to 05/31/2017. Pretreatment and post-treatment immunotherapy regimens, clinical symptoms, and examination findings were evaluated.

RESULTS

Median MGFA Class of II at baseline improved to an asymptomatic median classification at 12-months and last follow-up (p-values <.001) post-rituximab. Improvement in MGFA class was not significantly different between the groups. Twenty-one patients achieved clinical remission (12/17 AChR+, 9/16 MuSK+) with time to remission of 441.4 ± 336.6 days for AChR+ versus 230 ± 180.8 days for MuSK+ patients (p-value 0.049). The mean prednisone dosage requirement decreased significantly in both groups post-rituximab. AChR+ patients required more hospitalizations for exacerbation post-rituximab (p-value 0.046).

CONCLUSION

Rituximab treatment response is observed in both AChR+ and MuSK+ patients supporting the role of B cell depletion in the management of MG. While there was no significant difference between these groups in terms of clinical improvement, symptom-free state, and prednisone burden, MuSK+ MG patients may experience greater benefits, including earlier time to remission, fewer exacerbations and hospitalizations post-treatment.