A Case of Progressive Pulmonary Fibrosis due to Hypereosinophillic Syndrome

Progressive pulmonary fibrosis (PPF) describes interstitial lung disease (ILD) with a progressive fibrotic phenotype. Hypereosinophillic syndrome (HES) frequently involves the lung but rarely progresses to PPF-ILD. We report a 44-year-old man with a long-standing history of HES refractory to conventional management whose clinical course was complicated by progressive fibrotic ILD. Despite resolution of peripheral eosinophilia and treatment with corticosteroids, immunosuppressive therapy, anti–interleukin-5 therapy, and antifibrotic therapy, fibrotic lung disease continued to progress, culminating in severe pulmonary hypertension and end-stage lung disease. He developed refractory hypoxic respiratory failure, ultimately necessitating emergent combined heart–lung transplantation. This case highlights eosinophilic inflammation as a potential driver of progressive pulmonary fibrosis, even in the absence of peripheral eosinophilia, and underscores the importance of early recognition of fibrotic transformation and timely referral for advanced therapies in patients with HES.