Pleuroparenchymal Fibroelastosis in Connective Tissue Disease-Related Interstitial Lung Disease

Background: Pleuroparenchymal fibroelastosis (PPFE) is a rare fibroelastotic lung disease characterized histologically by dense pleural and subpleural fibrosis with upper-lobe predominance. In clinical practice, diagnosis often relies on characteristic radiologic findings, as surgical lung biopsy is rarely feasible. Unlike idiopathic pulmonary fibrosis, robust radiologic criteria validated against biopsy-proven cohorts remain limited, and the diagnostic performance of imaging alone is incompletely defined. Although initially described as idiopathic, PPFE is increasingly recognized in secondary settings, including connective tissue disease-associated interstitial lung disease (CTD-ILD), where it frequently overlaps with more common fibrotic patterns. Methods: We conducted a focused narrative review of the literature on PPFE in CTD-ILD, synthesizing evidence on morphology, epidemiology, clinical course, prognostic implications, and proposed pathobiological mechanisms, with emphasis on distinguishing true PPFE from PPFE-like lesions. Results: CTD-associated PPFE is associated with accelerated lung function decline, increased risk of pneumothorax, and poorer outcomes, particularly in systemic sclerosis and rheumatoid arthritis. However, distinguishing true PPFE from radiologic mimics remains challenging, and diagnostic approaches rely heavily on imaging without robust histopathologic validation. Proposed mechanisms include epithelial injury, immune dysregulation, and vascular or lymphatic abnormalities, although causal links remain unproven. Significant gaps persist regarding natural history and therapeutic responsiveness. Conclusions: Earlier identification of PPFE in CTD-ILD is important, as misclassification may delay risk stratification and management. Longitudinal imaging, multidisciplinary evaluation, and standardized diagnostic criteria are needed to improve clinical care and guide future research.