Effects of Changing Diagnosis Guidelines for Fibrotic Hypersensitivity Pneumonitis

Interstitial lung disease, CT scan
Investigators called for further research to evaluate the new diagnostic guideline of fHP in a real-world cohort of patients with chronic FILD.

Use of a new diagnostic guideline for hypersensitivity pneumonitis (HP), published in 2020, has resulted in half of patients with HP also being diagnosed with idiopathic pulmonary fibrosis (IPF), according to authors of a recent study published in the American Journal of Respiratory and Critical Care Medicine.

The investigators who conducted this retrospective observational cohort study sought to examine the consistency in clinical practice between the new diagnostic criteria for HP and other diagnostic criteria, such as for IPF. They therefore assessed the relationship between diagnosis based on the new HP guideline vs multidisciplinary discussion (MDD) diagnosis based on existing IPF guidelines and idiopathic interstitial pneumonia statements.  

They examined electronic medical records from consecutive patients with chronic fibrotic interstitial lung disease (FILD) who were undergoing surgical lung biopsy at a single hospital in Japan between January 2008 and August 2016. The high-resolution computed tomography scans and biopsy specimens on file were reanalyzed based on the new HP diagnostic guidelines.

Among the 280 consecutive patients with chronic FILD whose medical information was reviewed, MDD diagnoses based on existing IPF guidelines and idiopathic interstitial pneumonia statements were IPF in 137 patients and non-IPF FILD in 143 patients. The latter group included idiopathic nonspecific interstitial pneumonia in 32 patients, chronic HP in 27 patients, unclassifiable interstitial lung disease in 73 patients, and other diagnoses in 11 patients. Using the new guidance, a total of 95 patients were classified as having fibrotic HP (fHP), which included 20 patients with MDD-chronic HP.

The study authors noted that theirs “is the first study to evaluate the new diagnostic guideline of fHP in a real-world cohort of 280 chronic FILD patients,” adding that approximately half of patients determined to have fHP by the 2020 HP guideline also had a diagnosis of MDD-IPF, and approximately one-third of patients with MDD-IPF also had a diagnosis of fHP based on the new HP diagnostic guideline.

In conclusion, they emphasized that further research is needed “to elucidate the consistency between the IPF diagnostic criteria and the HP diagnostic criteria.”


Takei R, Yamano Y, Kataoka K, et al. New guideline diagnosis of fibrotic hypersensitivity pneumonitis in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med. Published online ahead of print May 25, 2021. doi:10.1164/rccm.202102-0407LE