Does a Type of Inciting Antigen Correlate with the Presence of Lung Fibrosis in Patients with Hypersensitivity Pneumonitis?

Introduction: Hypersensitivity pneumonitis (HP) is an interstitial inflammatory lung disease that develops as a result of exposition to various, mostly organic antigens. In some patients, fibrotic HP is diagnosed. Factors predisposing to the development of fibrotic lung disease in HP patients are not well documented in the literature. The genetic susceptibility of the patient, type of inciting antigen, and type of exposure, as well as various demographic and clinical variables, may influence the fibrotic process. Aim: The aim of the present study was to investigate whether the type of inciting antigen increases the risk of fibrotic lung disease in HP patients. Methods: Clinical data of consecutive patients with HP diagnosed between 2019 and 2023 were retrospectively reviewed. The exposition to the inciting antigens was investigated by the standardized questionnaire. Recent HP classification into fibrotic (fHP) and non-fibrotic (non-fHP) types was applied. Results: Sixty-six patients diagnosed with HP were analyzed. All patients filled out the exposure questionnaire, and 62 (94%) reported at least one possible exposure. The most prevalent exposures reported were avian, water systems, feather duvets, and hay/straw. Exposure to avian antigens as well as to coal/biomass heating were significantly more prevalent among patients with fHP compared to those with non-fHP (70% vs. 40%, p = 0.03 and 27% vs. 5%, p = 0.04, respectively). Nevertheless, in the multivariate analysis, older age at diagnosis was the only factor influencing the development of fHP (OR 1.064, 95% CI 1.004 to 1.138, p = 0.04). Reported avian antigen exposure correlated well with positive precipitins to avian antigens, whereas no correlation was found between hay/straw exposure and positive antibodies to termophilic actinomycetes. Conclusions: Exposure to birds and coal heating was the most frequently present factor in subjects with fHP, but only older age at diagnosis remained a significant fHP predictor in the multifactor analysis.