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.

Invasive tracheobronchial aspergillosis (ITBA) is a rare but severe form of invasive aspergillosis. This report presents a fatal case of ITBA in a 75-year-old man with a complex medical history including mediastinal lung adenocarcinoma, radiation pneumonitis, and pulmonary nocardiosis. The patient was admitted with worsening dyspnea and chest imaging revealed severe airway stenosis. Initially suspected to be cancer recurrence, post-mortem examination confirmed ITBA caused by Aspergillus penicillioides. Histopathological findings showed fungal invasion of the tracheobronchial tree with destruction, obstruction, and perforation of the airways. Multiple risk factors likely contributed to the development of ITBA in this patient, including diabetes, chronic obstructive pulmonary disease (COPD), long-term steroid use, prior COVID-19 infection, and a history of radiation therapy. This case highlights the diagnostic challenges of ITBA, particularly in patients with multiple comorbidities and a history of malignancy. It emphasizes the importance of considering fungal infections in the differential diagnosis of airway obstruction in high-risk patients.