Pleuroparenchymal fibroelastosis (PPFE) was first designated as a rare type of idiopathic interstitial pneumonia by WHO in 2013. Prior cases of “pulmonary upper lobe fibrosis (PULF)” and cases of “idiopathic upper lobe fibrosis” appear to be identical to FFPE.

Although the pathogenesis of PPFE has not been established, several potential initiating factors for have been reported, the commonest of which are bone marrow and hematopoietic stem cell transplantation and lung transplants. A history of chemotherapy treatment, autoimmune or connective tissue disease, acute lung injury particularly with infective complications, chronic hypersensitivity pneumonitis (HP), and occupational exposure to asbestos and aluminum have also been associated with PPFE. A history of pulmonary infections is frequently encountered in individuals with PPFE.

RADIOLOGY The characteristic radiologic findings are upper lobe pleural thickening with subpleural fibrosis and limited, if any, lower lobe involvement. Tractional distortion of the airways within areas of PPFE is common, reflecting the dense surrounding fibrosis. Lobar volume loss is common, and the radiographic changes may be progressive. Overt lung fibrosis of varying patterns can coexist with PPFE, most frequently UIP, NSIP, or HP. Anteroposterior associated flattening of the chest (platythorax) occurs commonly as does deepening of the suprasternal notch.; both are due to lung volume decrease and weight loss. Pneumothorax and pneumomediastinum may be seen. The commonest pattern of fibrotic ILD to coexist with PPFE is usual interstitial pneumonia (UIP), reported in one-fourth to one-half of cases (27, 31, 32). Coexistent UIP or even nonspecific interstitial pneumonia (NSIP) occurs most frequently in the lower lobes, away from the main areas of PPFE, but in common with the latter, each pattern will typically progress over time. PPFE has also been reported in patients diagnosed with chronic HP. PATHOLOGY A histopathological diagnosis of PPFE requires demonstration of intra-alveolar fibrosis and elastosis (IAFE), and visceral pleural fibrosis. The latter may be absent in biopsies because of its patchy distribution. IAFE comprises dense collagenous fibrosis filling alveolar spaces, with the residual alveolar walls highlighted by elastin deposition These features dominate in the upper lobes and are more readily seen on elastin van Gieson stain. Inflammation is typically mild and nonspecific. At low power, IAFE commonly appears just deep to the visceral pleura, although it may extend into the deeper parenchyma, typically around interlobular septa and bronchovascular bundles Foci of granulomatous inflammation may be present in approximately 15% of cases, although it is unclear whether granulomas represent a coexistent condition such as HP or infection. The differential diagnosis includes apical “cap,” radiation-induced lung injury, pulmonary paraquat toxicity, and chronic postinjury remodeling due to failure of acute respiratory distress syndrome to resolve. The clinical course of disease may be indolent, extending over several years or decades. However, in some patients the disease exhibits relatively rapid progression with death occurring in 5 years or less. There is currently no effective treatment for PPFE.