The effect of hypersensitivity pneumonitis guideline on the pathologic diagnosis of interstitial pneumonia

Abstract

Hypersensitivity pneumonitis (HP) and interstitial pneumonia (IP) have several overlapping characteristics, and a high diagnostic concordance rate of HP is rarely obtained. Thus, new guidelines, highly influenced by pathology, were devised for its diagnosis. We attempted to study the impact of the 2020 HP guidelines on pathological diagnosis of previously diagnosed cases of IP. Cases with fibrotic IP diagnosed in 2014 to 2019 were classified according to the 2020 HP guidelines into three categories: typical HP, probable HP, and indeterminate HP. The original pathological diagnosis and categorization based on the HP guidelines were compared. The clinical data including the serum data and the pulmonary function tests were compared among the groups. The study analyzed 247 consecutive cases classified into typical, probable, and indeterminate for HP, and alternative diagnoses. The number of cases that changed from an original diagnosis other than HP to HP based on the guidelines was 56 (23%). The clinical data of these cases bore greater resemblance to cases diagnosed as indeterminate for HP than those cases diagnosed as typical or probable HP. The ratios of typical and probable HP to those of the total cases were significantly low using cryobiopsy. Thus, with the application of the new guidelines, the pathological diagnosis of HP efficiently excluded HP cases but increased the rate of HP diagnosis for cases with fibrotic IP, which may not fit well to an HP diagnosis. Cryobiopsy may not be useful in imparting findings for fibrotic HP diagnosis using the new criteria.