Prognostic impact and factors associated with steroid-responsiveness in patients with hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an immune-mediated interstitial lung disease in which systemic corticosteroids remain first-line therapy despite limited evidence, especially in fibrotic forms. This study aimed to identify clinical, radiological, and biological features associated with functional response to steroids. We retrospectively analyzed 43 consecutive patients with HP treated with systemic corticosteroids and followed for at least 6 months. Patients were classified according to changes in forced vital capacity (FVC) as responders (≥5% increase), non-responders (≥5% decrease), or indifferent (±5%). Eighteen patients (42%) were responders, 15 (35%) indifferent, and 10 (23%) non-responders. Non-responders showed a consistently worse functional trajectory. A fibrosing high-resolution computed tomography pattern and baseline consolidations were more frequent in this group, as were precipitating antibodies against P. notatum and A. fumigatus. Conversely, bronchoalveolar lavage lymphocytosis >20% was more common among responders. Baseline FVC% and relative diffusing capacity of the lung for carbon monoxide were higher in non-responders, whereas demographic characteristics, smoking history, antigen exposure, comorbidities and autoantibody positivity did not differ significantly across groups. Fewer than half of patients experienced functional improvement after steroid therapy. Radiological fibrosis, consolidations, and specific precipitating antibodies were associated with lack of response, whereas bronchoalveolar lavage lymphocytosis predicted improvement. These findings highlight the heterogeneity of HP and may help identify patients unlikely to benefit from corticosteroids, supporting earlier consideration of alternative therapeutic strategies.