Is "Idiopathic" Pulmonary Fibrosis Overdiagnosed? "Idiopathic" Interstitial Lung Disease Associated with Inorganic Particulate Exposures — Evidence from Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopic Analyses
Zimin Zhao, Jerrold L Abraham. SUNY Upstate Medical University, Syracuse, NY
Background: Often pathologists diagnose interstitial pulmonary disease based solely upon routine light microscopic (LM) examination. Because epidemiologic studies show associations between environmental exposures and idiopathic pulmonary fibrosis (IPF), exclusion of such exposures prior to rendering a diagnosis of "idiopathic" pulmonary fibrosis is mandated. Brightfield and polarized LM only reveal a portion of inorganic particles. Scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) facilitates detection, characterization and quantification of inorganic particles, including many too small to be detected by LM. Such identification of potential causes of interstitial lung disease is important for proper diagnosis and prevention of disease.
Design: From 35 cases indexed as pulmonary fibrosis in consultation files (JLA) from 2005-2011, we extracted 21 cases having an initial diagnosis of idiopathic interstitial lung disease. We excluded cases with malignancy, overt silicosis, and those lacking adequate history and/or SEM/EDS analysis. We reviewed medical and occupational/environmental exposure histories, lung histopathology, and SEM/EDS particle analyses results, including the relative abundance of major particle types.
Results: Sixteen cases met the inclusion criteria. Most (13/16) were male. All had documented occupational/environmental exposures. The histopathology varied, including mild peribronchiolar fibrosis, usual interstitial pneumonia (UIP), giant cell interstitial pneumonia (GIP) and honeycombing. The predominant particle types (number of cases) found above background with SEM/EDS analyses were: silica (2), aluminum silicates (4), metals (including steel, Al, Sn, W) (5), talc (2), and asbestos fibers (2). One case revealed no increase in particles above background.
Conclusions: Light microscopic examination alone is insufficient to identify many particulate exposures. Also, even though 11/16 cases showed increased dust particles by brightfield and/or polarized LM, this was not considered by pathologists, and diagnoses of "idiopathic" were rendered. All of these cases, upon investigation, had histories of occupational/environmental exposures known to be capable of causing lung injury/fibrosis. Therefore, it is important that the diagnosis of "idiopathic" be reserved for cases in which such exposures have been excluded. We believe that public health would be enhanced by making pathologists and clinicians more aware of such cases.
Wednesday, March 21, 2012 9:30 AM
Poster Session V # 302, Wednesday Morning