Dynamic chest radiography-derived low-motion area ratio as a potential exploratory quantitative biomarker of idiopathic pleuroparenchymal fibroelastosis.

BACKGROUND

Idiopathic pleuroparenchymal fibroelastosis (iPPFE) is a rare type of idiopathic interstitial pneumonia characterized by upper-lobe-predominant pleural and subpleural fibrosis. Dynamic chest radiography (DCR) enables real-time assessment of respiratory motion using quantitative parameters such as diaphragm excursion, projected lung area, and low-motion area (LMA). However, its clinical utility in iPPFE remains unclear. We evaluated whether DCR-derived parameters, particularly the LMA ratio, reflect respiratory mechanical abnormalities in iPPFE.

METHODS

In total, 302 patients who underwent DCR were retrospectively analyzed. After excluding patients with chronic obstructive pulmonary disease, combined pulmonary fibrosis and emphysema, or preoperative thoracic malignancy, 107 patients were classified into the iPPFE, idiopathic pulmonary fibrosis, other interstitial lung diseases (ILDs), and control groups. The clinical characteristics, pulmonary function, and DCR parameters of the four groups were compared. Logistic regression analysis was performed to identify factors associated with iPPFE.

RESULTS

The iPPFE group had a significantly lower diaphragm excursion and change in projected lung area, and a significantly higher LMA and LMA ratio than the other groups. A low body mass index (BMI) and a high LMA ratio were independent factors associated with iPPFE. The difference in the LMA ratio remained significant after propensity score matching for age, sex, BMI, and %FVC between patients with iPPFE and those with non-iPPFE ILDs.

CONCLUSIONS

The LMA ratio is independently associated with iPPFE and may serve as an exploratory biomarker of impaired respiratory mechanics in iPPFE.