Physiological Criteria Are Useful for the Diagnosis of Idiopathic Pleuroparenchymal Fibroelastosis

Background: Diagnostic criteria of idiopathic pleuroparenchymal fibroelastosis (IPPFE) were recently proposed, including physiological criteria of the body mass index (BMI) and percentage of the predicted values of residual volume (RV)/total lung capacity (TLC) (RV/TLC %pred.). The aim of this study was to evaluate (i) whether the physiologic criteria are useful for the diagnosis and (ii) whether the flat chest index, defined as the ratio of the anteroposterior diameter to the transverse diameter of the thoracic cage, could be an alternative parameter to RV/TLC %pred. Methods: We selected consecutive IPPFE patients and idiopathic pulmonary fibrosis (IPF) patients. We examined the diagnostic sensitivity and specificity of the physiological criteria and flat chest index for differentiating IPPFE patients from IPF patients. Results: This study included 37 IPPFE patients and 89 IPF patients. The physiological criteria distinguished IPPFE patients from IPF patients with a sensitivity of 78.6% and specificity of 88.0%. The combination of the flat chest index and BMI was also effective for differentiation (sensitivity of 82.1% and specificity of 89.3%). Conclusion: We verified the good performance of the physiologic criteria in a different cohort. When the RV/TLC is not measured, using the flat chest index instead of RV/TLC %pred. may be reasonable.