A75-27 Spectrum of Radiological Bronchiolocentric Interstitial Pneumonia Patterns in a Large Japanese Interstitial Lung Disease Registry

Rationale

The PROMISE study is a nationwide interstitial lung disease (ILD) registry conducted at 133 tertiary referral centers accredited by the Japanese Respiratory Society, comprising 2,798 patients with ILD. In 2025, the Update of the International Multidisciplinary Classification of the Interstitial Pneumonias: A recent ERS/ATS Statement introduced bronchiolocentric interstitial pneumonia (BIP) as a major morphological pattern; however, its radiological framework and associated disease spectrum remain controversial. Although BIP imaging patterns have been reported to substantially overlap with radiologic features of hypersensitivity pneumonitis (HP), investigations of the disease spectrum encompassed within HP imaging patterns based on multidisciplinary discussion (MDD) incorporating clinical-radiologic (CR) or clinical-radiologic-pathologic (CRP) assessment remain limited.

Methods

Using the PROMISE registry, we identified patients whose high-resolution CT (HRCT) findings met criteria for a typical HP pattern (CT-T-HP-P) or a pattern compatible with HP (CT-C-HP-P) according to current HP guidelines. Both CT-T-HP-P and CT-C-HP-P were defined as radiological BIP patterns according to the recent ERS/ATS Statement. Among these patients, we evaluated the spectrum of CR diagnoses (CR-Dx), pathological diagnoses when available, and CRP diagnoses (CRP-Dx).

Result

Among 2,526 registered fibrotic-ILD patients, HRCT patterns were classified as CT-T-HP-P in 199 cases (7.8%), CT-C-HP-P in 797 cases (31.6%), and indeterminate for HP in 1,530 cases (60.6%). Among patients with CT-T-HP-P or CT-C-HP-P (996 cases), CR diagnoses included HP in 465 (46.7%), connective tissue disease associated ILD (CTD-ILD) in 58 (5.8%), drug induced lung injury in 4 cases (0.4%), aspiration related lung disease in none, and idiopathic disease in 260 (26.1%), including unclassifiable ILD (UC-ILD) in 184 (18.5%) followed by idiopathic pulmonary fibrosis (IPF) in 174 (17.5%). Histopathological evaluation, including transbronchial lung cryobiopsy and surgical lung biopsy, was performed in 400 (40.2%). Based on CRP diagnoses, HP was identified in 211 (52.8%), CTD-ILD in 13 (3.3%), and idiopathic disease in 172 (22.3%), including UC-ILD in 83 (20.8%) followed by IPF in 53 (13.3%). The concordance rate between CR and CRP diagnoses was 80.0% (Figure). Histopathology revealed BIP patterns, including airway-centered interstitial pneumonia, airway-centered interstitial fibrosis, bronchiolocentric interstitial pneumonia, or bronchiolocentric interstitial fibrosis, in 181 (45.3%).

Conclusion

Among patients with radiological BIP patterns, HP accounted for approximately one-half of cases, whereas UC-ILD and IPF comprised nearly one-third of the cohort. Histological BIP was identified in approximately half of the patients. These findings indicate that radiological BIP patterns encompass a heterogeneous disease spectrum, including a substantial proportion of UC-ILD and IPF.

This abstract is funded by: Boehringer Ingelheim