Differential Diagnosis of Fibrotic Hypersensitivity Pneumonitis with Its Non-Fibrotic Phenotype and Usual Interstitial Pneumonia During High-Resolution Computed Tomography

Background. Diagnosis of hypersensitivity pneumonitis (HP) using high-resolution computed tomography (HRCT) is not an easy task. The most difficult aspects of the disease include differential diagnosis of its fibrotic (fHP) and non-fibrotic (nfHP) phenotypes, as well as their differentiation from usual interstitial pneumonia (UIP) in idiopathic pulmonary fibrosis. The determination of fibrous changes at an early stage of development can significantly accelerate the beginning of antifibrotic therapy and improve the prognosis.

Objective: to identify key HRCT signs for reliable differentiation of fHP and nfHP, to carry out differential diagnostics between fHP and UIP.

Material and methods. The data of 73 patients with morphologically verified HP, in whom HRCT had been performed, were retrospectively analysed. In 21 patients, nfHP was determined, and in 52 patients fHP was identified. The comparison group consisted of 24 patients with a typical radiological UIP pattern. The analysis of the changes detected during HRCT was carried out by qualitative and semi-quantitative methods. The significance of qualitative differences in a sign manifestation was assessed by Fisher’s exact test, semi-quantitative differences were evaluated using Mann–Whitney test.

Results. The results of the study allow to assume, that the presence and degree of manifestation of certain HRCT signs significantly differ between the selected groups of patients in qualitative and/or semi-quantitative terms. In cases of НP, the distribution of changes was mostly uniform and diffuse, with no clear predominance in certain lobes. In UIP, diffuse craniocaudal distribution took place, and in the axial plane, the changes were mainly subpleural in nature.

Conclusion. Based on the results of the study, it can be assumed that fHP significantly differs from nfHP in such features as the presence and degree of manifestation of ground glass and honeycombing symptoms, reticular changes and traction bronchiectases. When comparing the fHP and UIP groups, the distinctive signs of fHP were centrilobular nodules, mosaic pattern, as well as diffuse axial sign distribution.

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