Abstract
BACKGROUND: Few studies have specifically examined on the second acute exacerbation (AE) in patients with fibrotic hypersensitivity pneumonitis (HP) and those with idiopathic pulmonary fibrosis (IPF). This study aimed to investigate the incidence and risk factors for the second AE. METHODS: This retrospective study included patients diagnosed histopathologically with fibrotic HP or IPF at Kanagawa Cardiovascular and Respiratory Center between January 2005 and June 2023. The incidence, risk factors, and 90-day survival following the second AE were analyzed. RESULTS: The cumulative incidence of the first AE was significantly lower in the fibrotic HP group compared with the IPF group [hazard ratio (HR) =0.561, 95% confidence interval (CI): 0.383-0.821, P=0.003]. For the second AE analysis, 39 patients with fibrotic HP and 61 patients with IPF were included. The 1-year incidence of the second AE, measured from 4 weeks after the first AE, was 23% in the fibrotic HP group and 29% in the IPF group (P=0.82). Multivariate analysis identified Krebs von den Lungen-6 (KL-6) levels measured 4 weeks after the first AE as a significant risk factor for the second AE in both fibrotic HP and IPF. The 90-day survival rate after the second AE was 69% for patients with fibrotic HP and 50% for patients with IPF (P=0.07, HR =0.503, 95% Cl: 0.232-1.091). CONCLUSIONS: Unlike the first AE, no significant difference in the second AE incidence was observed between fibrotic HP and IPF groups. Additionally, KL-6 levels measured 4 weeks after the first AE were identified as a risk factor for the second AE in both groups.