Spatial distribution of fibroblastic foci in transbronchial lung cryobiopsy specimens

Transbronchial lung cryobiopsy (TBLC) is the standard procedure for diagnosing interstitial lung disease (ILD). However, no morphology-based evaluation method has been established to assess clinical outcomes. Fibroblastic foci (FF), an important histopathological feature of idiopathic pulmonary fibrosis, are also observed in various ILDs, and their distribution may be useful for diagnosis. We examined whether the presence and distribution of FF in TBLC specimens have diagnostic utility and whether these features are associated with pulmonary function decline after TBLC. Among 198 patients who underwent TBLC, 46 with connective tissue disease-associated ILD (CTD-ILD), 53 with fibrotic hypersensitivity pneumonia (FHP), and 42 with idiopathic nonspecific interstitial pneumonia (INSIP) were analyzed to assess the diagnostic significance of FF. To explore whether FF findings were associated with pulmonary function decline across treatment modalities, 114 patients were classified into observation (n = 45), anti-inflammatory/immunosuppressive therapy (n = 50), and antifibrotic therapy (n = 19) groups. FF were classified as peripheral (pFF), alveolar (aFF), centrilobular (cFF), and distorted/dense fibrotic (dFF) lesions. The number of cFF-positive patients and the number of cFF were higher in CTD-ILD and FHP than in INSIP. The number of pFF-positive patients and the number of pFF were significantly higher among patients receiving antifibrotic therapy who experienced a ≥ 10% decline in percent predicted forced vital capacity at the 1-year follow-up after TBLC. Our results suggest cFF were more associated with CTD-ILD and FHP than with INSIP. The presence of pFF warrants further investigation as a potential feature associated with subsequent pulmonary function decline.