Utility of Blood Neutrophil to Diagnose Bacterial Infections under Satralizumab Treatment for Aquaporin-4 Antibody-positive Neuromyelitis Optica Spectrum Disorder: A Report of Two Cases.

Satralizumab is an anti-interleukin-6 receptor biologic that may mask bacterial infections. We report two patients with neuromyelitis optica spectrum disorder who developed afebrile bacterial infections with normal C-reactive protein levels during satralizumab treatment. During non-infectious periods under satralizumab treatment, the neutrophil count and neutrophil-to-lymphocyte ratio decreased, whereas the neutrophil change ratio, defined as the ratio of present to previous neutrophil counts, did not. At the time of infection, these variables were elevated compared to the intra-individual confidence intervals during non-infectious periods. These cases indicate the utility of neutrophil-related parameters in diagnosing bacterial infections during satralizumab treatment.