Pulmonary alveolar proteinosis-like change: A fairly common reaction associated with the severity of idiopathic pulmonary fibrosis

BackgroundWe have seen cases of chronic interstitial pneumonia (IP) with pulmonary alveolar proteinosis (PAP)-like changes that are focal histological features similar to PAP. To our knowledge, the association between PAP-like changes and chronic IP has not been investigated. We aimed to evaluate the incidence of PAP-like changes in chronic IP cases, and the association between the existence of PAP-like changes and the clinical features seen in patients with idiopathic pulmonary fibrosis (IPF).MethodsWe selected 144 cases of chronic IP that had a video-assisted thoracoscopic surgery biopsy between 2008 and 2011. Clinical records and hematoxylin and eosin-stained slides were reviewed, and clinicopathological findings, including the cumulative survival probability, were compared between IPF cases with and without a PAP-like change.ResultsA PAP-like change was identified in 20 of 144 cases (13.9%) of chronic IP and 14 of 61 IPF cases (23.0%). When comparing IPF cases with and without a PAP-like change, histological findings of honeycomb cysts and fibroblastic foci were associated with PAP-like changes (p=0.022 and 0.036, respectively). The percent-predicted values for forced vital capacity and diffusion capacity of carbon monoxide were lower (p=0.006 and 0.015, respectively), and concentrations of serum Krebs von den Lungen-6 and lactate dehydrogenase were higher (p=0.007 and 0.037, respectively) in cases of IPF with a PAP-like change than in those without one.ConclusionsThe presence of a PAP-like change in IPF cases was fairly common in our study, and may be a secondary reaction associated with IPF severity.