Idiopathic interstitial pneumonias: Clinical manifestations and pathology
- Carlyne D Cool, MD
Carlyne D Cool, MD
- Associate Professor of Medicine
- National Jewish Medical and Research Center
- Associate Clinical Professor of Pathology
- University of Colorado Denver, School of Medicine
- Section Editors
- Talmadge E King, Jr, MD
Talmadge E King, Jr, MD
- Editor-in-Chief — Pulmonary and Critical Care Medicine
- Section Editor — Interstitial Lung Disease
- Dean, School of Medicine
- Vice Chancellor, Medical Affairs
- University of California San Francisco
- Andrew Nicholson, MD
Andrew Nicholson, MD
- Section Editor — Pulmonary Pathology
- Professor of Respiratory Pathology
- Imperial College School of Medicine, London
"Diffuse interstitial lung disease" (ILD) is a generic term encompassing a broad range of largely unrelated conditions that share the propensity to cause breathlessness and/or cough associated with bilateral abnormal opacities of various types on conventional chest radiographs or computed tomographic (CT) scans (algorithm 1).
The idiopathic interstitial pneumonias are a subset of diffuse interstitial lung diseases of unknown etiology characterized by expansion of the interstitial compartment (ie, that portion of the lung parenchyma sandwiched between the epithelial and endothelial basement membranes) with an infiltrate of inflammatory cells. The inflammatory infiltrate is sometimes accompanied by fibrosis, either in the form of abnormal collagen deposition or proliferation of fibroblasts capable of collagen synthesis.
Our understanding of the idiopathic interstitial pneumonias has been plagued by our inability to clearly define the extent to which these represent distinct entities, as opposed to variations on the same fundamental theme. "Lumpers" have maintained that all are appropriately captured beneath the venerable umbrella of idiopathic pulmonary fibrosis (IPF, also referred to as cryptogenic fibrosing alveolitis [CFA]), and that morphologic separations are misguided attempts to segregate what are in fact highly related points on the same continuum of fibrosing lung disease. "Splitters" respond that failure to control for histologic subtypes has impeded our efforts to explain or predict the seemingly capricious behavior of a family of similar but separable interstitial lung diseases.
The pathologic classification of idiopathic interstitial pneumonias is reviewed here. In additional, clinical features of each type of idiopathic interstitial pneumonia are discussed. The diagnostic approach to patients with interstitial lung disease is presented elsewhere. (See "Approach to the adult with interstitial lung disease: Clinical evaluation" and "Approach to the adult with interstitial lung disease: Diagnostic testing".)
Averill Liebow pioneered the notion that morphologic characteristics are useful in separating idiopathic interstitial pneumonias into clinically and histologically distinct groups . These categories of usual interstitial pneumonia (UIP) and desquamative interstitial pneumonia (DIP) have persisted as important histologic groups, while bronchiolitis obliterans with classical interstitial pneumonia (BIP) and giant cell interstitial pneumonia (GIP) have disappeared from subsequent classification schemes (table 1) . The system outlined in the joint American Thoracic Society and European Respiratory Society statement on the histopathologic classification of idiopathic interstitial pneumonias further refines this terminology (table 2 and table 3) [3-5].
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- USUAL INTERSTITIAL PNEUMONIA
- Differential diagnosis
- DESQUAMATIVE INTERSTITIAL PNEUMONIA
- RESPIRATORY BRONCHIOLITIS-ASSOCIATED ILD
- Differential diagnosis
- SMOKING-RELATED INTERSTITIAL ABNORMALITIES
- ACUTE INTERSTITIAL PNEUMONIA
- NONSPECIFIC INTERSTITIAL PNEUMONIA
- LYMPHOID INTERSTITIAL PNEUMONIA
- CRYPTOGENIC ORGANIZING PNEUMONIA
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS