How Can Dupilumab Cause Eosinophilic Pneumonia?

Reports of eosinophilic pneumonia (EP) as a side effect of dupilumab administration are limited in previous studies. Herein, we report two cases in which EP developed subsequent to the administration of dupilumab for eosinophilic chronic rhinosinusitis (ECRS). Case 1: A 55-year-old woman presented with ECRS, eosinophilic otitis media, and bronchial asthma, and was treated with dupilumab for ECRS. Five weeks later, fever and dyspnea developed, and infiltration shadows were observed in her lungs. The peripheral blood eosinophil count (PBEC) was 3848/μL (26%), bronchoalveolar lavage fluid showed eosinophilic infiltration, and EP was subsequently diagnosed. Her condition improved following prednisolone treatment. Case 2: A 59-year-old man presented with fatigue and dyspnea after receiving dupilumab for ECRS. He had infiltrative shadows throughout his left lung field, and his PBEC was 4850/μL (26.5%). Prednisolone was initiated, and his condition improved. EP developed in both patients during the period of elevated PBEC after dupilumab administration, and dupilumab was suspected to be the causative agent in their EP. Hence, EP should be considered as a differential diagnosis when fever and dyspnea appear following dupilumab administration.