Upper lung asymmetry identifies distinct clinical phenotypes in idiopathic pleuroparenchymal fibroelastosis

Idiopathic pleuroparenchymal fibroelastosis (IPPFE) is a progressive interstitial lung disease characterized by upper lobe-predominant elastofibrosis. While disease asymmetry has been described in other interstitial lung diseases, its clinical significance in IPPFE remains unclear.

We evaluated 102 patients with IPPFE, 56 with idiopathic pulmonary fibrosis, and 50 healthy controls. Lung volumes were quantified using computed tomography to calculate the upper-lung asymmetry ratio (upper AR), defined as (combined volume of the right upper and middle lobe - left upper lobe volume) / predicted total lung capacity. Patients with IPPFE were classified as having asymmetrical IPPFE (AIPPFE) or symmetrical IPPFE (SIPPFE) based on the upper AR.

Asymmetry of lung volume was observed in 40.2% of patients with IPPFE (41/102), including right-dominant AIPPFE in 31.4% (32/102) and left-dominant AIPPFE in 8.8% (9/102). Compared with SIPPFE, right-dominant AIPPFE tended to be more frequent in male smokers. Left-dominant AIPPFE tended to be more frequent in non-smokers and was associated with an increased risk of pneumothorax, although the sample size was small. In the multivariate analysis, lower % predicted forced vital capacity and higher upper AR were identified as independent risk factors for pneumothorax; however, upper AR was not significantly associated with survival. The extent of tracheal deviation was significantly correlated with the upper AR (r = - 0.558, p < 0.001).

Asymmetry of upper lobe fibrosis is frequent in IPPFE, with distinct clinical characteristics based on the direction of predominance. The recognition of disease asymmetry in IPPFE may aid in risk stratification and clinical management.