Which Interstitial Lung Disease Respects the Pleura?
Most interstitial lung diseases actually spare the pleura rather than involve it, with the notable exception being Pleuroparenchymal Fibroelastosis (PPFE), which is unique in that it specifically involves both the pleura and subpleural lung parenchyma rather than respecting it. 1
Understanding Pleural Involvement vs. Pleural Sparing
The question of which ILD "respects" the pleura requires clarification of terminology:
Most ILDs spare (respect) the pleura: The typical ILDs like IPF/UIP, NSIP, and others generally do not involve the pleural surface itself, though they may have subpleural distribution of parenchymal disease 1
PPFE is the exception: This rare ILD is characterized by fibrosis that specifically involves the pleura and subpleural lung parenchyma, predominantly in the upper lobes 1
Key Distinguishing Features of PPFE
PPFE demonstrates dense subpleural consolidation with traction bronchiectasis, architectural distortion, and upper lobe volume loss on HRCT. 1, 2
Diagnostic HRCT Characteristics:
- Irregular pleural-based opacities in the upper lobes with associated reticular patterns and parenchymal distortion 2
- Dense subpleural consolidation with traction bronchiectasis 1, 2
- Upper lobe predominance (though lower lobe involvement may occur) 2
- The fibrosis is elastotic with intraalveolar fibrosis present histologically 1
Clinical Features to Recognize:
- Pneumothorax is common and should raise suspicion for PPFE 1, 2
- Approximately 50% of patients have experienced recurrent infections 1
- Median age of presentation is 57 years with no sex predilection 1
- Disease progression occurs in 60% of patients with death from disease in 40% 1
Clinical Context
PPFE can occur as an isolated entity or coexist with other ILDs, particularly IPF (seen in 6-10% of IPF cases). 2 When PPFE coexists with IPF, it is associated with more rapid decline in lung function, higher risk of pneumothorax and pneumomediastinum, and poorer survival 2
Important Caveat:
The subpleural and pleural-based distribution with elastotic fibrosis distinguishes PPFE from typical UIP patterns, which have subpleural predominance but do not involve the pleural surface itself 2