Relationship between fibroblastic foci and respiratory function: Does the abundance of fibroblastic foci reflect a recent decline in respiratory function?

Abstract

Aims

Fibroblastic foci (FF) are main findings in idiopathic pulmonary fibrosis (IPF) but are not specific to IPF. Pirfenidone and nintedanib are standard antifibrotic treatments for IPF and affect factors associated with fibroblasts. A proportion of interstitial lung diseases (ILDs) are progressive fibrosing ILDs (PF-ILDs). This progressive fibrosing phenotype includes various ILDs, including fibrotic hypersensitivity pneumonitis (FHP) and connective tissue disease-related ILD (CTD-ILD). We examined the relationship between FF and a relative decline in respiratory function.

Methods and results

Among patients with lung transplantation (LT), those diagnosed with IPF, nonspecific interstitial pneumonia (NSIP), CTD-ILD, and FHP for whom respiratory function test results within 24 months before LT were retrospectively available were included (n = 67). Patients were classified as PF-ILD+ or PF-ILD- based on the criteria for the progression of a relative decline in the predicted value of forced vital capacity (FVC) within 24 months before LT. We classified FF into peripheral (pFF), alveolar (aFF), centrilobular (cFF), and distorted or dense fibrotic lesions (dFF). The number of FF/cm² at each location was counted, and its percentage was calculated. Spearman's rank correlation coefficient between a relative decline in %FVC and total FF/cm² in NSIP was 0.721. The dFF/cm² and dFF/total FF ratios were higher and the aFF/total FF ratio was lower in the PF-ILD+ group than in the PF-ILD- group.

Conclusion

Total FF correlated with relative declines in %FVC in NSIP. Higher dFF/total FF ratios were associated with progressive status, and higher aFF/total FF ratios were associated with less progressive status.