Decrease in Urinary Tract Infections Following Switch From Anti-Interleukin-6 Monoclonal Antibody to Ravulizumab in a Patient With Neuromyelitis Optica Spectrum Disorder (NMOSD): A Case Report

Satralizumab is an anti-interleukin-6 (IL-6) monoclonal antibody used for the treatment of neuromyelitis optica spectrum disorder (NMOSD). Although mild urinary tract infections (UTIs) or respiratory tract infections during immunotherapy may appear benign, they can progress to serious infections such as sepsis. We report a case of a 65-year-old woman with NMOSD who is currently under regular follow-up at our hospital and receiving biologic therapy. She was diagnosed with anti-aquaporin 4 antibody-positive NMOSD at the age of 53 and experienced multiple relapses thereafter. Approximately 10 years after disease onset, satralizumab was initiated, after which she developed recurrent UTIs. After switching to ravulizumab, the incidence of UTIs was halved despite no significant changes in prednisolone dose, HbA1c level, or urinary glucose level. The clinical course suggested a close association between satralizumab treatment and recurrent UTIs. This case highlights the potential increased susceptibility to recurrent UTIs associated with anti-IL-6 monoclonal antibody therapy. Clinicians should monitor for recurrent UTIs in NMOSD patients treated with satralizumab and consider alternative treatments, such as C5 complement inhibitors, if infections persist.