Small airways impairment and air-trapping distinguish chronic hypersensitivity pneumonitis (CHP) from idiopathic pulmonary fibrosis (IPF)

Introduction In a recent multidisciplinary study, there was major disagreement between expert groups on the diagnosis of CHP, with IPF the major differential diagnosis. Identification of physiological differences that characterize small airways (SA) dysfunction and air-trapping (AT) might help narrow a diagnosis of CHP when atypical clinic-radiological attributes are present. Aim To evaluate key differences in SA dysfunction and AT in CHP compared to IPF. Methods Pulmonary function tests of patients with multidisciplinary diagnoses of CHP and IPF (n=118 each) of matched disease severity (% predicted FVC: 69.3±21.9 vs. 73.8±16.2, p=n/s and % predicted TLco: 39.2±14.8 vs 39.9±13.1, p=n/s) were retrospectively retrieved at the Royal Brompton Hospital. Indices related to SA and AT were compared. Data were analyzed using parametric tests following testing for normal distribution and expressed as mean±SD. A p-value Results Compared to the IPF cohort, CHP patients showed worse SA impairment as evidenced by lower % predicted values of MEF25, MEF50 and MEF75 (p Conclusions CHP differs from IPF in terms of SA function and AT. In future, integration of these characteristics with assessment of disease behavior, volumetric radiology and dynamic small airway tests may improve the accuracy of the often elusive diagnosis of CHP.