We identified 116 NMOSD patients who were treated with a median annual dose of 2,077 milligrams of rituximab (IQR=1673-2710mg) for a median of 4.6 years (IQR=2.4-8.0). The majority (88%) were aquaporin-4 IgG seropositive. Fifty-eight (50%) patients received an induction dose of 1g or less. The most common initial rituximab maintenance dose was 1g every 6 months (n=80, 69%), with 22 (19%) receiving lower and 14 (12%) higher doses. Rituximab dosing was lowered in 34 (29%) and increased in 6 (5.2%) patients. Twenty-one (18%) relapsed following rituximab treatment, of which 7 occurred within 6 months of initiation. Patients who relapsed had similar demographic and clinical characteristics at rituximab initiation and there were no significant differences in induction, initial maintenance or median annual doses compared to relapse-free patients. Six patients (5.2%) died within 2 years of their most recent rituximab dose, 3 from advanced NMO and 1 from COVID-19 pneumonia. Rituximab was discontinued in 28 (24%) patients, 10 (8.6%) for infections, 5 relapses, 2 hypogammaglobulinemia, 2 infusion reactions and 2 for disease stability.

We found that annual rituximab dose of ~2gm adequately controlled disease activity in >95% of NMOSD patients yet led to discontinuation from infections or hypogammaglobulinemia in 10.3% in this diverse, population-based cohort. Taken together with the existing literature, these findings indicate that even lower rituximab doses may result in an improved risk/benefit profile.