Clinically occult subpleural fibrosis and acute interstitial pneumonia a precursor to idiopathic pulmonary fibrosis?

Background and objective: The clinical features and acute component of the pathological findings in patients with acute exacerbation of IPF are similar to those of acute interstitial pneumonia (AIP). A growing body of research suggests that acute exacerbation of subclinical IPF is similar to AIP. This study tested the hypothesis that subpleural fibrosis (resembling localized usual interstitial pneumonia) in patients with diffuse alveolar damage can mimic patients with AIP alone. Methods: The clinical, radiological and histopathological characteristics of patients with AIP with or without subpleural fibrosis, as identified at post-mortem examination, were assessed. Results: Fourteen patients with AIP met the inclusion criteria. These comprised nine men and five women ranging in age from 65 to 90 years. The mean duration from onset of symptoms to admission was 12.3 days, and from admission to death was 50.5 days. All patients presented with severe respiratory failure with bilateral pulmonary infiltrates on CXR. CT scans revealed bilateral ground glass opacity (100.0%), air space consolidation (69.2%) and no honeycombing. In seven patients (50.0%) histological examination showed subpleural fibrosis. There were no differences in the clinicopathological or CT scan findings between patients with AIP only compared with those with AIP and subpleural fibrosis. Conclusions: Subpleural fibrosis resembling localized usual interstitial pneumonia is often present in patients diagnosed as having AIP. These patients were not distinguishable from those with AIP only, based on the clinicopathological and radiological findings.