Outcomes of a Typical Fibrotic Hypersensitivity Pneumonitis Pattern on Chest Computed Tomography.

Rationale: Guidelines have defined a "typical hypersensitivity pneumonitis (HP)" imaging pattern for fibrotic HP (fHP); however, the frequency, characteristics, and outcomes of different multidisciplinary diagnoses within this pattern are unknown. Objectives: The goal of this study was to describe the frequency at which different multidisciplinary diagnoses present with a typical fHP pattern and to identify clinically relevant differences across these diagnoses. Methods: Patients with a typical fHP pattern on chest computed tomography (CT) were identified from a prospective registry. Multidisciplinary diagnoses were established by consensus during a research-dedicated standardized multidisciplinary discussion of all available data. Prespecified diagnostic categories of interest included fHP with an exposure identified, fHP without an exposure identified, and connective tissue disease-associated interstitial lung disease (CTD-ILD), with each diagnosis defined by >50% likelihood after this structured multidisciplinary discussion. Clinical and radiological features and outcomes were compared across multidisciplinary diagnoses. Measurements and Main Results: Of 164 patients with CT patterns of typical fHP, 49 had multidisciplinary diagnoses of fHP with probable or possible exposures identified (30%), 56 had fHP without exposures identified (34%), 36 had CTD-ILD (22%), and 23 had other multidisciplinary diagnoses (14%). Clinical and CT features differed across multidisciplinary diagnoses. Lung function decline and time to death or transplantation were worse in patients with fHP without probable or possible exposures. Positive autoimmune serologies or new rheumatologist-confirmed CTD diagnoses developed in 14% of patients with fHP without exposures identified during follow-up. Conclusions: Patients with a typical fHP pattern on chest CT frequently have non-HP diagnoses (most often CTD-ILD), have differences in baseline characteristics and disease behavior across multidisciplinary diagnoses, and more frequently develop features of CTD during follow-up when an initial HP exposure is not identified.