Overview of Interstitial Lung Disease: Interstitial Lung Diseases: Merck Manual Professional


	Sections		Pulmonary Disorders

	Chapters		Interstitial Lung Diseases

Overview of Interstitial Lung Disease

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).

Among the numerous possible causes are most connective tissue disorders and occupational lung exposures and many drugs (see Environmental Pulmonary Diseases and Table 1: Interstitial Lung Diseases: Causes of Interstitial Lung Disease). A number of interstitial lung diseases of unknown etiology have characteristic histology, clinical features, or presentation and thus are considered unique diseases, including eosinophilic pulmonary diseases, pulmonary Langerhans cell histiocytosis (granulocytosis), lymphangioleiomyomatosis, pulmonary alveolar proteinosis, and sarcoidosis. 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.

Table 1

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Causes of Interstitial Lung Disease
Category	Examples
Connective tissue disorders	Ankylosing spondylitis (rare) Behçet syndrome (very rare) Dermatomyositis and polymyositis Goodpasture syndrome Mixed connective tissue disease RA Sjögren syndrome SLE Systemic sclerosis Undifferentiated connective tissue disease
Drugs	Selected list: Amphotericin B, bleomycin, busulfan, carbamazepine, chlorambucil, cocaine, cyclophosphamide, diphenylhydantoin, flecainide, heroin, melphalan, methadone, methotrexate, methylphenidate, methysergide, mineral oil (via chronic microaspiration), nitrofurantoin, nitrosoureas, procarbazine, silicone (sc injection), tocainide, vinca alkaloids (with mitomycin)
Occupational and environmental exposure	Inorganic (selected): Aluminosis (caused by exposure to metallic aluminum powder), asbestosis, baritosis, berylliosis, coal workers' pneumoconiosis, exposure to hard metals (eg, cadmium, cobalt, titanium oxide, tungsten, vanadium carbides), radiation fibrosis, siderosis, silicosis, stannosis, talc pneumoconiosis Organic (selected): Bagassosis, bird fancier's lung, coffee worker's lung, farmer's lung, hot tub lung, humidifier lung, malt worker's lung, maple bark stripper's lung, mushroom worker's lung, tea grower's lung
Infections	Aspergillosis Histoplasmosis Parasitic infection Mycobacterial infection Viral infection
Vasculitis	Eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome) Giant cell arteritis (rare) Granulomatosis with polyangiitis (formerly Wegener granulomatosis) Microscopic polyangiitis Polyarteritis nodosa (rare) Takayasu arteritis (rare)
Idiopathic interstitial pneumonias	Acute interstitial pneumonia Cryptogenic organizing pneumonia Desquamative interstitial pneumonia Idiopathic pulmonary fibrosis Lymphocytic interstitial pneumonia Nonspecific interstitial pneumonia Respiratory bronchiolitis–associated interstitial lung disease
Miscellaneous disorders	Amyloidosis Chronic aspiration Eosinophilic pneumonia Gaucher disease (rare) Lipoid pneumonia Lymphangioleiomyomatosis Microlithiasis Neurofibromatosis Niemann-Pick disease (rare) Pulmonary alveolar proteinosis Pulmonary Langerhans cell histiocytosis (granulomatosis) Pulmonary lymphoma Sarcoidosis Tuberous sclerosis

Last full review/revision April 2013 by Harold R. Collard