Clinical Predictors and Histologic Appearance of Acute Exacerbations in Chronic Hypersensitivity Pneumonitis

Background: Acute exacerbations (AEs) in idiopathic pulmonary fibrosis (IPF) are critical factors for its clinical course and prognosis. We have seen AEs and poor prognosis consequent to AE in patients with chronic hypersensitivity pneumonitis (HP), as has been seen in patients with IPF. The aim of this study was to evaluate the clinical features of the patients with AE in those with chronic UP. Methods: We reviewed 100 consecutive patients with chronic bird fancier lung (BFL) from 1993 to 2006, and analyzed the clinical characteristics, including history, and laboratory and immunologic, imaging, BAL, and histologic findings. Results: AE developed in 14 patients during this observation period (AE group), whereas 86 patients remained stable (non-AE [NAE] group). The 2-year frequency of AE among patients with chronic BFL having usual interstitial pneumonia (UIP)-like lesions seen on surgical lung specimens was 11.5%. Patients with AE were more likely to be smokers (p = 0.003). In pulmonary function test results, the mean total lung capacity (TLC) and diffusing capacity of the lung for carbon monoxide (DLCO) were lower in patients with AEs (TLC: AE patients, 63.0 +/- 16.8%; NAE patients, 81.6 +/- 20.0%; DLCO: AE patients, 41.9 +/- 19.0%; NAE patients, 60.0 +/- 19.4%). The mean number of lymphocytes in BAL fluid were lower (AE patients, 13.7 +/- 7.5 lymphocytes; NAE patients, 37.2 +/- 29.7 lymphocytes), while the number of neutrophils were greater in AE patients (AE patients, 10.7 +/- 17.6 neutrophils; NAE patients, 3.6 +/- 4.4 neutrophils). Histologic and/or radiologic findings revealed that all AE patients had UIP-like lesions. Diffuse alveolar damage was observed in six cases, whereas organizing pneumonia superimposed on preexistent fibrotic lesions was observed in two cases. Conclusions: The present study showed several predictive factors for AE at the time of diagnosis. Low TLC and DLCO, low lymphocyte levels in BAL fluid, and a UIP-like pattern in histology at the time of diagnosis may be the risk factors for AE. (CHEST 2008; 134:126,5-1270)