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.
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.
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:
Drugs such as nitrofurantoin, amiodarone, bleomycin, and many others can rarely cause interstitial lung disease.
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.
The most common symptom of all forms of interstitial lung disease is shortness of breath. Nearly all people with interstitial lung disease will experience breathlessness, which may get worse over time.
Other symptoms of interstitial lung disease include:
In most forms of interstitial lung disease, the shortness of breath develops slowly (over months). In interstitial pneumonias or acute interstitial pneumonitis, symptoms come on more rapidly (in hours or days).
People with interstitial lung disease usually come to see a doctor due to concern about shortness of breath or cough. Imaging tests of the lungs are usually done to identify the problem.
Chest X-ray: A simple chest X-ray is the first test in the evaluation of most people with a breathing problem. Chest X-ray films in people with interstitial lung disease may show fine lines in the lungs.
Computed tomography (CT scan): A CT scanner takes multiple X-rays of the chest and a computer creates detailed images of the lungs and surrounding structures. Interstitial lung disease can usually be seen on a CT scan.
High-resolution CT scan: If interstitial lung disease is suspected, using certain CT scanner settings can improve the images of the interstitium. This increases the CT scan's ability to detect interstitial lung disease.
Pulmonary function testing: A person sits in a sealed plastic booth and breathes through a tube. People with interstitial lung disease may have a reduced total lung capacity. They may also have a decreased ability to transfer oxygen from their lungs into their blood.
Lung biopsy: Often, obtaining lung tissue to examine under a microscope is the only way to determine which type of interstitial lung disease a person has. There are several ways to collect lung tissue, which is called a lung biopsy:
Treatments for interstitial lung disease vary according to the type of interstitial lung disease and its cause.
Antibiotics: These are effective treatments for most interstitial pneumonias. Azithromycin (Zithromax) and levofloxacin (Levaquin) eliminate the bacteria that cause most interstitial pneumonias. Viral pneumonias usually resolve on their own. Fungal pneumonias are rare, but can be treated with antifungal drugs.
Corticosteroids: In some forms of interstitial lung disease, ongoing inflammation in the lungs causes damage and scarring. Corticosteroids like prednisone and methylprednisolone reduce the activity of the immune system. This reduces the amount of inflammation in the lungs and the rest of the body.
Inhaled oxygen: In people with low oxygen blood levels due to interstitial lung disease, inhaled oxygen may improve symptoms. Regular use of oxygen might also protect the heart from damage caused by low oxygen levels.
Lung transplant: In advanced interstitial lung disease causing severe impairment, a lung transplant may be the best option. Most people undergoing lung transplant for interstitial lung disease make large gains in quality of life and their ability to exercise.
Azathioprine (Imuran): This drug also suppresses the immune system. It has never been proven to improve interstitial lung disease, but some studies suggest it might help.
N-acetylcysteine (Mucomyst): This potent antioxidant may slow the decline of lung function in some forms of interstitial lung disease. It should not be used alone.
Other treatments considered controversial for the treatment of interstitial lung disease include:
These medicines suppress the immune system significantly. They may be used in some cases of interstitial lung disease while monitoring for side effects.