Asbestosis and environmental causes of usual interstitial pneumonia

Abstract

Purpose of review: Recent epidemiologic investigations suggest that occupational and environmental exposures contribute to the overall burden of idiopathic pulmonary fibrosis (IPF). This article explores the epidemiologic and clinical challenges to establishing exposure associations, the current literature regarding exposure disease relationships and the diagnostic work-up of IPF and asbestosis patients.

Recent findings: IPF patients demonstrate a histopathologic pattern of usual interstitial pneumonia. In the absence of a known cause or association, a usual interstitial pneumonia pattern leads to an IPF diagnosis, which is a progressive and often terminal fibrotic lung disease. It has long been recognized that asbestos exposure can cause pathologic and radiographic changes indistinguishable from IPF. Several epidemiologic studies, primarily case control in design, have found that a number of other exposures that can increase risk of developing IPF include cigarette smoke, wood dust, metal dust, sand/silica and agricultural exposures. Lung mineralogic analyses have provided additional support to causal associations. Genetic variation may explain differences in disease susceptibility among the population.

Summary: An accumulating body of literature suggests that occupational and environmental exposure can contribute to the development of IPF. The impact of exposure on the pathogenesis and clinical course of disease requires further study.

FIGURE 1. Asbestosis high-resolution chest CT scan

(a) HRCT lung windows demonstrate lower lobe predominant disease with evidence of reticular markings and honeycombing. (b) Mediastinal windows reveal evidence of pleural thickening and calcfiications (Courtesy of Jonathan Killam, MD and Ami Rubinowitz, MD). CT, computed tomography.

FIGURE 2. Histopathology of usual interstitial pneumonia

(a) Reveals a low-power UIP view showing temporal heterogeneity with areas of abnormal lung alternating with normal lung. (b) Reveals a fibroblast focus representing an area of active fibroblast proliferation typically seen in UIP patients (Courtesy of Robert Homer, MD, PhD). UIP, usual interstitial pneumonia.

FIGURE 3. Asbestos body

Asbestos bodies seen on iron stained section represent asbestos fibers surrounded by a coating of iron and protein. Definitive identification of the enclosed fibers requires scanning electron microscopy and energy dispersive X-ray analysis (Courtesy Robert Homer, MD, PhD).