Organizing pneumonia following ocrelizumab therapy in a patient with multiple sclerosis: A case report and comprehensive literature review

Introduction Ocrelizumab, an anti-CD20 monoclonal antibody, has revolutionized the treatment of multiple sclerosis (MS). While generally safe, it has been rarely associated with organizing pneumonia (OP), a form of interstitial lung disease linked to immune modulation. Case presentation We report a 48-year-old woman with relapsing MS who developed persistent fever, dry cough, and exertional dyspnea six months after her fourth ocrelizumab infusion. Imaging revealed bilateral consolidations and ground-glass opacities. Extensive microbiological and autoimmune workup, including bronchoalveolar lavage, excluded alternative etiologies. The patient was found to have marked hypogammaglobulinemia (IgG 192 mg/dL, IgA 24 mg/dL, IgM 8 mg/dL). A clinical diagnosis of OP with a suspected association with ocrelizumab was established based on characteristic clinical and radiologic findings after exclusion of alternative etiologies, without histopathologic confirmation. She was treated with intravenous immunoglobulin (0.4 g/kg/day for 5 days) and oral prednisolone (1 mg/kg/day for 2 months), resulting in complete clinical and radiological resolution. Ocrelizumab was discontinued, and no pulmonary recurrence or MS relapse was observed during 6-month follow-up. Conclusion Through a structured literature review, seven previously reported cases of ocrelizumab-associated OP were identified. Our case adds to this limited body of evidence and is one of the few to describe marked hypogammaglobulinemia at diagnosis, successfully managed with combined corticosteroid and immunoglobulin therapy. Prompt recognition and tailored immunosuppressive treatment can lead to favorable outcomes. Awareness of this rare complication is crucial as the use of ocrelizumab continues to expand.