High-resolution CT features distinguishing usual interstitial pneumonia pattern in chronic hypersensitivity pneumonitis from those with idiopathic pulmonary fibrosis

Purpose Radiologic diagnosis of chronic hypersensitivity pneumonitis (CHP) presenting a usual interstitial pneumonia (UIP) pattern is challenging. The aim of this study was to identify the high-resolution CT (HRCT) findings which are useful to discriminate CHP-UIP from idiopathic pulmonary fibrosis (IPF). Materials and methods This study included 49 patients with well-established bird-related CHP-UIP, histologically confirmed, and 49 patients with IPF. Two groups of observers independently assessed HRCT, evaluated the extent of each abnormal HRCT finding. When their radiological diagnosis was CHP-UIP, they noted the HRCT findings inconsistent with IPF. Results Correct CT diagnoses were made in 79% of CHP-UIP and 53% of IPF. Although no apparent difference was seen in the extent of each HRCT finding, upper or mid-lung predominance, extensive ground-glass abnormality, and profuse micronodules were more frequently pointed out as inconsistent findings in CHP-UIP than IPF (p = 0.007, 0.010, 0.001, respectively). On regression analysis, profuse micronodules [OR 13.34 (2.85-62.37); p = 0.001] and upper or mid-lung predominance of findings [OR 2.86 (1.16-7.01); p = 0.022] remained as variables in the equation. Conclusion In this cohort, some IPF cases were misdiagnosed as CHP-UIP. Profuse micronodules and upper or mid-lung predominance are important clues for the differentiation of CHP-UIP from IPF.