Acute Exacerbation and Proposed Criteria for Progressive Pulmonary Fibrosis in Patients with Fibrotic Hypersensitivity Pneumonitis and Idiopathic Pulmonary Fibrosis

Acute exacerbation (AE) occasionally develops in the course of fibrotic hypersensitivity pneumonitis (HP).The aim of the study was to compare AE of fibrotic HP with that of idiopathic pulmonary fibrosis (IPF).Consecutive patients with pathologically confirmed fibrotic HP and IPF diagnosed based on a multidisciplinary discussion were included in the analysis. AE in patients with fibrotic HP and IPF was evaluated retrospectively.This study included 309 and 160 patients with fibrotic HP and IPF, respectively. Their 50% survival times were 96.1 and 78.0 months, respectively (hazard ratio [HR]: 0.54 [95% confidence interval, CI: 0.36-0.77], log-rank test; p < 0.001). Notably, the cumulative AE rates of fibrotic HP were 3% at 1 year and 10% at 3 years. Moreover, the corresponding rates of IPF were 8% at 1 year and 20% at 3 years (HR: 0.66 [95% CI: 0.45-0.93], log-rank test; p = 0.034). The 90-day survival rates from the AE onset of fibrotic HP and IPF were 75% and 64%, respectively (HR: 0.51 [95% CI: 0.31-0.83], log-rank test; p = 0.006). The respiratory function test on the physiological criteria of progressive pulmonary fibrosis (PPF) was a predictor of AE in fibrotic HP. However, the high-resolution CT (HRCT) changes in the criteria of PPF were not. Nevertheless, both the physiological and radiological criteria of PPF were a predictor of AE of IPF.AE of fibrotic HP has a lesser prognostic effect than that of IPF. HRCT criteria for PPF were not a risk factor for AE in patients with fibrotic HP.