Merck Manual

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Overview of Interstitial Lung Disease

(Diffuse Parenchymal Lung Diseases)


Joyce Lee

, MD, MAS, University of Colorado School of Medicine

Reviewed/Revised Jun 2021 | Modified Sep 2022
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Interstitial lung diseases are a heterogeneous group of disorders characterized by alveolar septal thickening, fibroblast proliferation, collagen deposition, and, if the process remains unchecked, pulmonary fibrosis. Interstitial lung diseases can be classified using various criteria (eg, acute vs chronic, granulomatous vs nongranulomatous, known cause vs unknown cause, primary lung disease vs secondary to systemic disease, history of smoking vs no smoking history).

In up to 30% of patients who have interstitial lung diseases with no clear cause, the disorders are distinguished primarily by characteristic histopathologic features; these disorders are termed the idiopathic interstitial pneumonias Overview of Idiopathic Interstitial Pneumonias Idiopathic interstitial pneumonias (IIPs) are interstitial lung diseases of unknown etiology that share similar clinical and radiologic features and are distinguished primarily by the histopathologic... read more .

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