Delayed-Onset Rituximab Lung Injury in Neuromyelitis Optica Spectrum Disorder: A Case Report

Background: Rituximab (RTX) is a monoclonal antibody targeting CD20 on B cells. It has been used for many years as an effective off-label treatment for patients with neuromyelitis optica spectrum disorder (NMOSD). A serious, rare adverse effect of rituximab is interstitial lung disease (ILD), mainly reported in patients with lymphoma receiving combination therapy. Here, we report a progressive and fatal case of rituximab-induced interstitial lung disease (RTX-ILD) in a patient with NMOSD. Case presentation: A 34-year-old man with a history of aquaporin-4 (AQP4)-positive NMOSD was hospitalized for severe dyspnea and a nonproductive cough. He has been receiving RTX, 1000 mg intravenously every six months, for the past three years with no previous complications. Pulmonary symptoms progressed despite outpatient care, and imaging revealed ground-glass opacities and pleural effusion. After excluding infectious causes, drug-induced pneumonitis was suspected, and corticosteroid therapy was initiated. However, the patient died of progressive respiratory failure. Conclusion: RTX-ILD is a rare, potentially fatal adverse effect that should be considered in patients with NMOSD receiving RTX who develop respiratory symptoms. This complication may occur even after RTX therapy that was previously well tolerated.