Neutropenia Associated With B Cell-Depleting Therapies in Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder.

Background And Objectives: Neutropenia is described as a rare adverse event associated with B cell-depleting therapy (BCDT) use in patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). However, little is known about longitudinal clinical outcomes. We estimated the real-world incidence of neutropenia among patients with neuroinflammatory disease treated with BCDT and characterized the clinical course.

Methods: We conducted a retrospective cohort study using electronic medical records to estimate the incidence rate of neutropenia in adults with MS/NMOSD from a neuroimmunology clinic in California between January 6, 2006, and November 2, 2015, treated with ocrelizumab, rituximab, ofatumumab, ublituximab, or inebilizumab. Each clinical course (recurrence, time to recovery of absolute neutrophil count [ANC], postneutropenia treatment) of neutropenia was then presented in a case series.

Results: In this cohort of 1,825 patients (6,009 person-years on BCDT), the largest cohort addressing this question to date, 37 developed neutropenia. The estimated incidence rate of neutropenia was 0.62 (95% CI 0.45-0.85) per 100 person-years. The median time from last infusion of current BCDT was 4 months (interquartile range [IQR] 1-6). The median nadir ANC was 390 (IQR 40-960); the nadir ANC was 0 for 6 patients (16%). All patients ultimately recovered to normal counts, except 2 patients developing fluctuating ANCs for months. Among the 32 patients not receiving filgrastim, the median time to ANC recovery was 11 days (95% CI 7-26). Course severity was asymptomatic/mild in 32% (n = 12) while 54% (n = 20) required hospitalization. A confirmed simultaneous infection or infectious prodrome occurred in 23 (62%). After recovery, 30 patients (81%) continued BCDT and 2 (7%) changed within BCDT class. Neutropenia recurred in 13 patients (35%), including 3 who discontinued BCDT after initial neutropenia. The estimated incidence rate of recurrent neutropenia was 0.22 (95% CI 0.13-0.39) per 100 person-years. The mean (SD) time to recurrence from initial neutropenia was 251 (SD: 355) days.

Discussion: This study is comprehensive and reflects a large cohort, examining incidence rates of neutropenia with BCDT in MS and NMOSD. Overall, neutropenia was still rare, occurring at a rate of 0.66 per 100 person-years, and infections were associated triggers in some patients. Yet, of relevance to clinicians, neutropenia was not benign: half required hospitalization and 35% experienced recurrence, which is higher than what was reported in clinical trials.