Interstitial lung disease is a general category that includes many different lung conditions. All interstitial lung diseases affect the interstitium, a part of the lungs' anatomic structure.
The interstitium is a lace-like network of tissue that extends throughout both lungs. The interstitium provides support to the lungs' microscopic air sacs (alveoli). Tiny blood vessels travel through the interstitium, allowing gas exchange between blood and the air in the lungs. Normally, the interstitium is so thin it can't be seen on chest X-rays or CT scans.
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All forms of interstitial lung disease cause thickening of the interstitium. The thickening can be due to inflammation, scarring, or extra fluid (edema). Some forms of interstitial lung disease are short-lived; others are chronic and irreversible.
Some of the types of interstitial lung disease include:
Interstitial pneumonia: Bacteria, viruses, or fungi may infect the interstitium of the lung. A bacterium called Mycoplasma pneumonia is the most common cause.
Idiopathic pulmonary fibrosis: A chronic, progressive form of fibrosis (scarring) of the interstitium. Its cause is unknown.
Nonspecific interstitial pneumonitis: Interstitial lung disease that's often present with autoimmune conditions (such as rheumatoid arthritis or scleroderma).
Hypersensitivity pneumonitis: Interstitial lung disease caused by ongoing inhalation of dust, mold, or other irritants.
Cryptogenic organizing pneumonia (COP): A pneumonia-like interstitial lung disease but without an infection present. COP is also called bronchiolitis obliterans with organizing pneumonia (BOOP).
Acute interstitial pneumonitis: A sudden, severe interstitial lung disease, often requiring life support.
Desquamative interstitial pneumonitis: An interstitial lung disease that's partially caused by smoking.
Sarcoidosis: A condition causing interstitial lung disease along with swollen lymph nodes, and sometimes heart, skin, nerve, or eye involvement.
Asbestosis: Interstitial lung disease caused by asbestos exposure.
Causes of Interstitial Lung Disease
Bacteria, viruses, and fungi are known to cause interstitial pneumonias. Regular exposures to inhaled irritants at work or during hobbies can also cause some interstitial lung disease. These irritants include:
Coal dust, or various other metal dusts from working in mining
Grain dust from farming
Bird proteins (such as from exotic birds, chickens, or pigeons)
All told, these factors cause a small percentage of interstitial lung disease. The cause of most interstitial lung disease is unknown.
Who is at risk from interstitial lung disease? Anyone can develop interstitial lung disease. Men and women of any age can be affected. Interstitial lung disease is more common in people with autoimmune disease, including lupus, rheumatoid arthritis, and scleroderma.