Ocrelizumab-related organizing pneumonia in multiple sclerosis: insights from a case series and literature review

Background Organizing pneumonia (OP) is a rare interstitial lung disease that may occur secondary to drug exposure. Although OP has been described during rituximab treatment, the association with ocrelizumab remains elusive, with evidence limited to a few recent cases. We aimed to characterize ocrelizumab-related OP in the context of the existing literature. Methods Clinical, radiological, laboratory, therapeutic, and outcome data were retrospectively collected from multiple sclerosis (MS) patients with ocrelizumab-associated OP at our center and descriptively compared with 17 cases identified through a literature review. Results Among 626 ocrelizumab-treated MS patients, five cases of OP were observed (0.8%) (3 females, median age=54 years, range=27–64). OP developed after a mean treatment exposure of 5.1 years (standard deviation (SD=2.9) and a mean interval of 10.8 weeks (SD=10.4) following the last infusion. Clinical presentation was characterized by persistent antibiotic-refractory fever, sometimes accompanied by nonproductive cough. Chest CT consistently showed patchy groundglass opacities and consolidations. All patients received prednisone 0.5–1 mg/kg/day for a median duration of 30 days (range=15–60), followed by gradual tapering. Despite initial clinical response, respiratory relapses and residual radiological lung abnormalities were observed in four patients during a median follow-up of 29 months (range=4–47). Ocrelizumab was discontinued in all patients. Only one patient initiated ozanimod two years after OP onset. Discussion Our findings support the emerging evidence of ocrelizumab-related OP and show substantial consistency with previously reported cases. Further studies are needed to clarify the potential role of CD20+ lymphocyte depletion in OP pathogenesis.