Clinical characteristics and prognosis of patients with acute exacerbations of idiopathic interstitial pneumonia: factor and cluster analyses

Acute exacerbation of idiopathic interstitial pneumonia (AE-IIP) is a major cause of death in patients with idiopathic pulmonary fibrosis (IPF) or related conditions. Various individual clinical indicators have been reported as prognostic indicators of AE-IIP; however, composite parameters may allow more accurate prediction of prognosis. We retrospectively analyzed patients admitted to two university hospitals with AE-IIP between January 2007 and March 2021. Exploratory factor analysis was conducted using 22 clinical, laboratory, and radiological indicators, followed by cluster analysis using factor scores. Eighty-four patients (median age, 76 years; 71 [85%] males) admitted for AE-IIP, including 60 (71%) patients with IPF, were included in the analysis. Exploratory factor analysis identified four components associated with usual interstitial pneumonia/IPF, systemic inflammatory response syndrome, lung injury, and smoking-related disease, respectively. Cluster analysis using the factor scores of these four components identified four clusters that demonstrated significantly different mortality rates within 90 days of admission (P = 0.006). Overall, this study suggests that the assessment of the four components composed of multiple clinical, laboratory, and radiological indicators may help classify AE-IIP cases into four clusters with potentially different short-term prognoses.