The similarities and differences between pleuroparenchymal fibroelastosis and idiopathic pulmonary fibrosis

The idiopathic form of pleuroparenchymal fibroelastosis (PPFE) is categorized as a rare idiopathic interstitial pneumonia in the current classification. The majority of PPFE cases are idiopathic, but many predisposing factors or comorbidities have been reported. Although histological PPFE is predominantly located in the upper lobes, which are less often affected by fibrosis in patients with idiopathic pulmonary fibrosis (IPF), the clinical course of PPFE is seemingly similar to that of IPF. However, upper lobe fibroelastosis has various clinical and physiological characteristics that differ from those of IPF, including a flattened thoracic cage and a marked decrease in the forced vital capacity (FVC) but with a preserved residual volume. Compared with IPF, the decrease in the walking distance is mild despite the markedly decreased FVC in PPFE, and chest radiograph more frequently shows the elevation of bilateral hilar opacities with or without tracheal deviation. The prognosis may be related to the development of fibrosing interstitial pneumonia in the lower lobes with elevated levels of serum Krebs von den Lungen-6; however, there is marked variation in the pathogenesis and clinical features in PPFE. A proposal of the diagnostic criteria for idiopathic PPFE with and without surgical lung biopsy, which has recently been published, may be useful.