Proliferation of elastic fibres in idiopathic pulmonary fibrosis: a whole-slide image analysis and comparison with pleuroparenchymal fibroelastosis.

Aims: We occasionally encounter patients with idiopathic pulmonary fibrosis (IPF) who have similar imaging patterns to those of pleuroparenchymal fibroelastosis (PPFE) in the upper lung fields but are not diagnosed as having PPFE clinically. The aim of this study is to identify the clinicopathological features and intrapulmonary distribution of elastic fibres and collagen fibres in these patients.

Methods And Results: We retrospectively reviewed the medical records of patients with a clinical diagnosis of IPF, and selected consecutive patients who underwent autopsy or pneumonectomy for lung transplantation. Patients with histologically confirmed PPFE were also reviewed for comparison. We quantified the collagen fibres and elastic fibres in each lobe as a percentage of the non-aerated lung area (collagen fibre score and elastic fibre score, respectively) in histological specimens by using whole-slide image analysis, and compared these scores between IPF and PPFE patients. In a total of 55 patients (IPF, 48; PPFE, 7), there were no significant differences in the collagen fibre scores between IPF and PPFE patients. The elastic fibre scores in the upper lobe in PPFE patients were significantly higher than those in IPF patients (23.5 versus 10.3, P = 0.005). However, it is of note that, in 12 of 48 IPF patients, the elastic fibre scores of the upper lobes were above the first quartile of those in PPFE patients.

Conclusions: IPF occasionally shows intense elastosis in the upper lobes, and such cases are histologically indistinguishable from PPFE. There seem to be histologically borderline cases between PPFE and IPF.