Challenges in Recognizing Airway-Centered Fibrosis: Observer Concordance and Its Role in Fibrotic Hypersensitivity Pneumonitis.

BACKGROUND:The interobserver agreement regarding airway-centered fibrosis (ACF), the key diagnostic feature of fibrotic hypersensitivity pneumonitis (fHP) has not been sufficiently addressed to date. We applied digital image analysis to investigate this issue and extracted histological features of ACF to correlate with fHP diagnosis. METHODS:A total of 111 selected glass slides from 17 fHP and 30 idiopathic pulmonary fibrosis (IPF) were scanned and seven expert pulmonary pathologists were tasked with digital annotation of ACF. Interobserver agreement on annotated ACF was assessed using Fleiss' kappa value. ACF recognized by majority of pathologists (4 or more) were considered as consensus ACF (cACF), and their frequencies were compared between fHP and IPF cases. RESULTS:Fleiss' kappa agreement in ACF recognition was 0.32 among seven pathologists. A significant difference between cryobiopsy and VATS specimens regarding an average ACF count per slide (p = 0.012) was found. The number of cACFs in a single case ranged from 0 to 20 (mean 5.71) for fHP cases and 0 to 13 (mean 1.80) for IPF cases (p = 0.011). When limited to surgical biopsies, the average number of cACF was 10.3 for fHP vs. 1.68 for IPF (p < 0.001). The common characteristic features of cACF in fHP were their confinement to the vicinity of respiratory bronchioles, frequent association with peribronchiolar metaplasia, and mild to moderate lymphocytic infiltration. CONCLUSIONS:The recognition of ACF varies widely among pathologists. We identified common histologic features of ACF in fHP cases, proposing criteria for ACF recognition in fHP.