Long-Term Prognosis and Transition Period until Progression in Fibrotic Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is an interstitial lung disease that may present as fibrotic (fHP) or non-fibrotic (nfHP). Fibrosis is associated with progression and poor outcomes; however, the transition to progressive pulmonary fibrosis (PPF) and its predictors remain unclear.

We retrospectively reviewed adult patients diagnosed with HP at a tertiary hospital (2010 and 2022). Patients were classified as having fHP or nfHP and were followed up for at least 1 year. Clinical, functional, radiological, and histological variables were analyzed. PPF was defined according to the 2022 clinical practice guideline of the American Thoracic Society (ATS), European Respiratory Society (ERS), Japanese Respiratory Society (JRS), and Asociación Latinoamericana de Tórax (ALAT).

Of 298 HP patients, 191 were included (153 fHP and 38 nfHP). Among patients with fHP, 76 (49.7%) developed PPF after a median of 3.2 years. Median survival was 4.8 years in fHP with PPF versus 6.3 years without, with 1.6 years from PPF onset to death or transplantation. The independent predictors of PPF and survival were lower forced vital capacity, elevated lactate dehydrogenase, fibroblastic foci, and microscopic honeycombing.

Nearly half of fHP patients progressed to PPF within a few years, with markedly reduced survival. Early recognition of high-risk patients may support timely antifibrotic treatment and improve outcomes.