Background and objective: Fibroblastic foci (FF) composed of an accumulation of fibroblasts or myofibroblasts may be related to the progression of pulmonary fibrosis leading to respiratory insufficiency. Several studies have shown that the number of FF is a significant prognostic factor in usual interstitial pneumonia (UIP). The purpose of the present study was to examine whether the extent of FF is related to impairment of respiratory function and prognosis in patients with biopsy-proven fibrosing interstitial pneumonia, including UIP and fibrotic non-specific interstitial pneumonia (fNSIP). Methods: Fifty patients with histologically confirmed interstitial pneumonia including UIP or fNSIP were investigated, and correlations between FF and pulmonary function were evaluated. FF area was calculated as the proportion of total area (%FF) and the number of FF (FF/cm2) in the whole histological specimen from each patient. Results: The UIP group showed significantly higher %FF and FF/cm2 than the fNSIP group. When UIP and fNSIP patients were analysed together, the group of patients who had died (death group) revealed significantly higher %FF and FF/cm2 compared with the group of survivors, and the impairment of vital capacity and diffusing capacity of carbon monoxide was correlated with %FF and FF/cm2. Conclusions: FF correlated with impaired pulmonary function and may be a useful parameter to predict prognosis in patients with UIP and fNSIP. A significant correlation was demonstrated between histological findings and respiratory function in fibrosing interstitial pneumonia. Our findings indicate that fibroblastic foci are a reliable predictor of prognosis in usual interstitial pneumonia and fibrotic non-specific interstitial pneumonia.
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