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

Background: 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.

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. Pre-specified 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.

Results: Of 164 patients with a CT pattern of typical fHP, 49 had a multidisciplinary diagnosis of fHP with a probable or possible exposure identified (30%), 56 had fHP without an exposure (34%), 36 had a CTD-ILD (22%), and 23 had another multidisciplinary diagnosis (14%). Clinical and CT features differed across multidisciplinary diagnoses. Lung function decline and time to death or transplant were worse in fHP without a probable or possible exposure. Positive autoimmune serologies or a new rheumatologist-confirmed CTD diagnosis developed in 14% of patients with fHP without an exposure identified during follow-up.

Conclusion: 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.