Interstitial (in-tur-STISH-ul) lung disease actually describes a group of disorders, most of which cause progressive scarring of lung tissue. This eventually affects your ability to breathe and get enough oxygen into your bloodstream. Beyond this, the disorders vary greatly.

Most cases of interstitial lung disease develop gradually, but some come on suddenly. Doctors can pinpoint why some cases of interstitial lung disease occur, but many have no known cause.

In all cases, once lung scarring occurs, it's generally irreversible. Medications occasionally can slow the damage of interstitial lung disease, but many people never regain full use of their lungs. Researchers hope that newer drugs, many still experimental, may eventually prove more effective in treating interstitial lung disease.

Signs and symptoms of the wide variety of disorders classified as interstitial lung disease may include:

• A feeling of breathlessness (dyspnea), especially during or after physical activity
• A dry cough
• Wheezing
• Chest pain
• Fingernails that curve over the tops of your fingertips (clubbing)

Breathlessness and a dry cough are often the primary signs and symptoms. Because these problems are vague and tend to develop gradually — often long after you have irreversible lung damage — you may assume they are due to aging, asthma, being overweight or out of shape, smoking, or the lingering effects of an upper respiratory infection.

Symptoms tend to become progressively worse. Eventually you may notice you're getting out of breath during routine activities — getting dressed, talking on the phone, even eating. At this point, breathing problems become impossible to ignore.

When to see a doctor
By the time signs and symptoms such as breathlessness and cough appear, irreversible lung damage has often already occurred. Nevertheless, it's important to see your doctor at the first sign of breathing problems. Many conditions other than interstitial lung disease can affect your lungs, and getting an early and accurate diagnosis is important for proper treatment.

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Airways and air sacs of the lungs

Each time you inhale, air travels to your lungs through major airways called bronchi. Inside your lungs, the bronchi subdivide into smaller airways (bronchioles) that finally end in clusters of tiny air sacs (alveoli). Within the walls of the air sacs are small blood vessels (capillaries), where oxygen is added to your blood and carbon dioxide — a waste product of metabolism — is removed.

Scarring of tiny air sacs
In interstitial lung disease, the walls of the air sacs may become inflamed, and the tissue (interstitium) that lines and supports the sacs becomes increasingly thickened and scarred. Normally, the air sacs are highly elastic, expanding and contracting like small balloons with each breath. But scarring (fibrosis) causes the thin, interstitial tissue to become stiffer and thicker, making the air sacs less flexible. Instead of being soft and elastic, scarred air sacs have the texture of a stiff sponge, which makes it more difficult to breathe and harder for oxygen to enter your bloodstream through the thickened walls.

Abnormal healing response
Scarring in interstitial lung disease seems to occur when an injury to your lungs triggers an abnormal healing response. Ordinarily, your body generates just the right amount of tissue to repair damage. But in interstitial lung disease, the repair process goes awry, producing excess scar tissue that increasingly interferes with lung function.

One disorder, many causes
Because interstitial lung disease has a wide range of causes, determining the reason for an initial injury to lung tissue can be difficult. Some of the many possible contributing factors include:

• Occupational and environmental factors. Long-term exposure to a number of toxins or pollutants can lead to serious lung damage. Workers who routinely inhale silica dust, asbestos fibers or hard metal dust are especially at risk of serious lung disease. So are people exposed to certain chemical fumes and ammonia or chlorine gases.

  But chronic exposure to a wide range of substances, many of them organic, also can damage your lungs. Among these are grain, sugar cane, and dust from bird and animal droppings. Other substances, such as moldy hay, can be a problem when they cause a hypersensitivity reaction in the lungs (hypersensitivity pneumonitis). Even bacterial or fungal overgrowth in poorly maintained humidifiers and hot tubs can cause lung damage.

• Infections. These include viral infections such as cytomegalovirus, a particular problem if you have a weakened immune system; some bacterial infections, including pneumonia; fungal infections such as histoplasmosis; and parasitic infections.
• Radiation. Some people who receive radiation therapy for lung cancer or breast cancer show signs of lung damage long after they finish radiation treatment. The severity of the damage may depend on how much of your lung is exposed to radiation, the total amount of radiation you receive, whether chemotherapy also is used, and whether you have underlying lung disease.
• Drugs. Some drugs can damage the tissue that lines your lungs. Those most likely to cause lung problems include chemotherapy drugs, medications used to treat heart arrhythmias and other cardiovascular problems, certain psychiatric medications, and some antibiotics.
• Other medical conditions. Interstitial lung disease can occur with other disorders. Often, those conditions don't directly attack the lungs, but instead affect tissue processes throughout the body. Among these are lupus, scleroderma, rheumatoid arthritis, dermatomyositis, polymyositis, Sjogren's syndrome and sarcoidosis. Some researchers think that gastroesophageal reflux disease (GERD) — in which the lungs chronically intake a small volume of gastric contents — can result in pulmonary fibrosis.

When the cause isn't known
Although doctors can determine why some people develop interstitial lung disease, in many cases the cause isn't known. Disorders without a known cause are grouped together under the label idiopathic pulmonary fibrosis or idiopathic interstitial lung disease. Although the idiopathic diseases have certain features in common, each also has unique characteristics.

Usual interstitial pneumonitis, also called idiopathic pulmonary fibrosis, is the most common of the idiopathic interstitial lung diseases. Because usual interstitial pneumonitis develops in patches, some areas of the lungs are normal, others are inflamed and still others are marked by scar tissue. The disease affects more men than women and usually develops in people over age 50.

Other, less common types of idiopathic pulmonary fibrosis include:

• Nonspecific interstitial pneumonitis
• Bronchiolitis obliterans with organizing pneumonia (BOOP)
• Respiratory bronchiolitis-associated interstitial lung disease
• Desquamative interstitial pneumonitis
• Lymphocytic interstitial pneumonitis
• Acute interstitial pneumonitis

Factors that may make you more susceptible to interstitial lung disease include:

• Age. Interstitial lung disease is much more likely to affect adults, although infants and children sometimes develop the disorder. Idiopathic forms of the disease usually develop in adults older than 50.
• Exposure to occupational and environmental toxins. If you work in mining, farming or construction or for any reason are exposed to pollutants known to damage your lungs, your risk of interstitial lung disease greatly increases.
• Radiation and chemotherapy. Having radiation treatments to your chest or using some chemotherapy drugs makes it more likely that you'll develop lung disease.
• Oxygen. Continually inhaling very high levels of therapeutic oxygen for more than 48 hours can harm the lungs.

Risk factors for idiopathic interstitial lung disease
Researchers have identified certain factors that appear to increase the risk of idiopathic lung disease, even though the cause of the disorder isn't yet known:

• Smoking. Some forms of interstitial lung disease are more likely to occur in people with a history of smoking, and active smoking may make the condition worse. The risk seems to increase with the number of years and the number of cigarettes smoked. However, with rare exceptions, smoking does not directly cause interstitial lung disease.
• Genetic factors. One rare type of idiopathic interstitial lung disease runs in families. Called familial pulmonary fibrosis, it's similar to other forms of the disease. Although research is being done on familial pulmonary fibrosis, researchers haven't yet identified the genes that may be involved.
• Gastroesophageal reflux disease (GERD). Researchers are investigating a possible link between idiopathic interstitial lung disease and gastroesophageal reflux disease. In GERD, stomach acid or, occasionally, bile salts back up into your esophagus and are then drawn into your lungs (aspirated) in droplets.

Scar tissue formation in your lungs can lead to a series of life-threatening complications, including:

• Low blood oxygen levels (hypoxemia). Because interstitial lung disease reduces the amount of oxygen you take in and the amount that enters your bloodstream, you're likely to develop lower than normal blood oxygen levels. Lack of oxygen can severely disrupt your body's basic functioning.
• High blood pressure in your lungs (pulmonary hypertension). Unlike systemic high blood pressure, this condition affects only the arteries in your lungs. It begins when scar tissue restricts the smallest blood vessels, limiting blood flow in your lungs. This in turn raises pressure within the pulmonary arteries. Pulmonary hypertension is a serious illness that becomes progressively worse.
• Right-sided heart failure (cor pulmonale). This serious condition occurs when your heart's lower right chamber (right ventricle) — which is less muscular than the left — has to pump harder than usual to move blood through obstructed pulmonary arteries. Eventually the right ventricle fails from the extra strain.
• Respiratory failure. In the end stage of chronic interstitial lung disease, respiratory failure occurs when severely low blood oxygen levels along with rising pressures in the pulmonary arteries cause heart failure.

You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to a lung disorders specialist called a pulmonologist.

Because appointments can be brief and because there's often a lot of ground to cover, it's a good idea to be well prepared for your appointment. Here's some information to help you get ready and on what to expect from your doctor.

What you can do

• Note any symptoms you're experiencing. For interstitial lung disease, it will help your doctor to have as many details as possible about when your symptoms first appeared and how they may have changed or worsened over time.
• Write down possible occupational exposure to lung irritants. Consider every job you can remember since you started working. Your doctor will be especially interested to know if any work experiences, even many years ago, involved exposure to dusts, gases or chemicals.
• Write down possible environmental exposure to lung irritants. It will help your doctor to know if your symptoms appeared after contact with common bacteria-harboring culprits such as hot tubs, humidifiers or water damaged carpet. Also tell your doctor about exposure to pets, especially birds.
• Make a list of your key medical information, including other conditions you're being treated for and the names of the medications that you're currently using or have used in the last two years. Include on your list prescription drugs, over-the-counter drugs, vitamins, herbs and supplements. Be sure to tell your doctor if you've used laxatives or nose drops containing mineral oil.
• Take film from any chest X-rays you've had in the last 10 years. It will help your doctor make a diagnosis if he or she can compare an old chest X-ray with the results of a current scan. The actual X-ray film is more important to your doctor than is the report. If your primary care physician had a chest X-ray done as part of your initial evaluation, bring that with you when you see a pulmonologist.
• Take a family member or friend along, if possible. Sometimes it can be difficult to soak up all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

During your first visit with your doctor, he or she will be focused on gathering information about your symptoms and medical history and ordering tests. You'll likely return for a later visit to review test results and talk about treatment options.

For interstitial lung disease, some basic questions to ask your doctor at your initial appointment include:

• What is likely causing my symptoms or condition?
• Are there any other possible causes for my symptoms or condition?
• What kinds of tests do I need?
• How will you monitor my condition over time?
• Will it help if I stop smoking now?
• If the people I live with smoke, will it aggravate my condition?
• Can I continue to work?
• I have these other health conditions. How can I best manage them together?
• Are there any restrictions that I need to follow?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Think about your answers ahead of time. Your doctor may ask:

• When did you first begin experiencing symptoms?
• How quickly have your symptoms gotten worse?
• Are your symptoms persistent, or do they seem to disappear and then reappear?
• Have you had a fever or chills?
• Have you ever coughed up blood?
• Have you ever done any of the following types of work: mining, machine tool grinding, sandblasting, working with granite, welding, working in a shipyard, working in the aerospace or electronic industries, or farming?
• Have any current or former colleagues been diagnosed with lung conditions caused by irritants in the work environment?
• Have you recently had new contact with the following: air conditioners, humidifiers, pools, hot tubs, or water-damaged walls or carpet?
• Have any close relatives or friends been diagnosed with a related condition?
• Do you come into contact with birds through your work or hobbies? Does a neighbor raise pigeons?
• Do you have any family history of lung disease?
• Do you or did you smoke? If so, how much?
• Have you been diagnosed or treated for any other medical conditions? When?

What you can do in the meantime
If you smoke or share a home with people who smoke, try to cut back on your exposure to smoke while you wait for your appointment. The symptoms of any lung condition are made worse by inhaling smoke. No matter what your diagnosis, if you smoke, work with your doctor to make a plan for stopping.

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Spirometer

Identifying and determining the cause of interstitial lung disease can be extremely challenging. An unusually large number of disorders fall into this broad category. What's more, the distinction between interstitial lung disorders with identifiable causes and those with no known cause isn't always clear.

In addition, the signs and symptoms of a wide range of medical conditions — among them chronic obstructive pulmonary disease (COPD), heart failure and asthma — can mimic interstitial lung disease, and doctors must rule these out before making a definitive diagnosis.

To help cut through the confusion and rule out other possible illnesses, your doctor is likely to begin with a detailed medical history and physical exam. Once certain conditions have been ruled out, your doctor will recommend tests such as:

• Chest X-ray. Although this is often the first test given in cases of suspected lung problems, a chest X-ray isn't as effective as a computerized tomography (CT) scan in diagnosing interstitial lung disease. It can, however, help eliminate conditions that cause signs and symptoms similar to those of interstitial lung disease, including emphysema and a collapsed lobe of one of the lungs.
• High-resolution computerized tomography (HRCT) scan. Whereas a traditional chest X-ray produces two-dimensional images of your lungs, a CT scan uses an X-ray-sensing unit and a large computer to create cross-sectional images that are far more detailed. An HRCT scan goes even further, showing lung tissue in great detail and providing more information than conventional CT scans do.
• Pulmonary function tests (PFTs). These noninvasive tests check how well your lungs function. For the test, you're usually asked to blow into a simple instrument called a spirometer, which measures how much air your lungs can hold and the flow of air out of your lungs. As scarring becomes worse, you're able to take less air in and blow less out. Some pulmonary function tests also measure the amount of gas exchanged across the membrane between your alveoli and capillary blood vessels.
• Exercise tests. Because symptoms of interstitial lung disease are worse when you're active, your doctor may assess your lung function while you exercise, usually on a stationary bike or treadmill. Although specific tests vary, your blood pressure and blood oxygen levels are usually monitored as the difficulty of the exercise increases.
• Bronchoscopy (transbronchial biopsy). In many cases, interstitial lung disease can be definitively diagnosed only by examining a small amount of lung tissue (biopsy). In a transbronchial biopsy, your doctor passes a flexible, fiber-optic tube (bronchoscope) through your mouth into your lungs and removes one or more tissue samples, each about the size of the head of a pin. These are then examined in a laboratory. Bronchoscopy is performed on an outpatient basis using local anesthesia.
• Bronchoalveolar lavage. In this procedure, your doctor injects salt water (saline) through a bronchoscope into a section of your lung and then immediately suctions it out. The withdrawn solution contains cells from the air sacs. Although bronchoalveolar lavage samples a larger area of the lung than other procedures do, it may not provide enough information to diagnose a specific interstitial lung disease. Instead, doctors often use it to check the progress of a lung disorder or to help determine the best treatment.
• Video-assisted thoracoscopic surgery. When less invasive tests don't yield a specific diagnosis, a thoracic surgeon may perform a surgical lung biopsy. In this procedure, a flexible tube with a camera (endoscope) is inserted through a small incision between your ribs, allowing the surgeon to view your lungs on a video monitor. Surgical instruments are then inserted through another incision, and the surgeon removes thumbnail-sized tissue samples from two or three sites in your lungs.

Interstitial lung disease caused by toxins or drugs can sometimes be reversed when you're no longer exposed to those substances. But in people for whom this isn't the case, the outlook is less promising. That's because the drug therapies that are currently available can have serious side effects and often aren't effective.

Treatment for interstitial lung disease often includes a combination of the following medications:

• Corticosteroid drugs. These anti-inflammatory drugs help a minority of people with interstitial lung disease. Those most likely to benefit have a disorder with a known cause and reversible changes in their lungs. Corticosteroids seldom improve lung function in people with idiopathic pulmonary fibrosis, and when they do, the benefits are usually temporary.

  Taken for long periods of time or in large doses, corticosteroids can cause a number of side effects, including glaucoma, bone loss, high blood sugar levels leading to diabetes, poor wound healing and increased susceptibility to infection.

• Azathioprine. This cytotoxic medication, which is normally used to prevent organ rejection after a transplant, may also be used in combination with corticosteroids to treat interstitial lung disease. Azathioprine can cause severe side effects, including reduced production of red blood cells and an increased risk of infection and certain cancers. Another cytotoxic drug, cyclophosphamide, may be tried if azathioprine is not effective. However, the side effects associated with cyclophosphamide are even more severe.
• Acetylcysteine. This medication belongs to a class of drugs called antioxidants. Oxidation is a natural process that leads to cell and tissue damage. The process may play a role in the development of scarring in the lungs (pulmonary fibrosis). Results from a clinical trial found that, when combined with corticosteroids and azathioprine, acetylcysteine improved lung function in people with idiopathic pulmonary fibrosis. No significant changes were seen in mortality rates.
• Anti-fibrotics. These drugs are sometimes used to help reduce the development of scar tissue. In clinical studies, the medications bosentan and pirfenidone have shown promise for slowing the progression of lung damage. Follow-up studies to gain more information about the risks and benefits of these drugs in the treatment of interstitial lung disease are under way. Other anti-fibrotic agents that have been studied as possible treatments for this condition — including penicillamine, colchicine and interferon gamma-1b — have not been found effective.
• Oxygen therapy. Depending on the severity of your symptoms and your activity level, your doctor may recommend oxygen therapy. Although oxygen can't stop lung damage, it can make breathing and exercise easier and prevent or lessen complications from low blood oxygen levels. Oxygen therapy may also improve your sleep and sense of well-being. It can also reduce blood pressure in the right side of your heart.

• Pulmonary rehabilitation. This is a formal program for people with chronic lung disease that includes, but goes far beyond, medical management. The aim of pulmonary rehabilitation is not only to treat a disease or even improve daily functioning, but also to help people with pulmonary fibrosis live full, satisfying lives. Pulmonary rehabilitation programs focus on exercise, teaching you how to breathe more efficiently, education, and emotional support and nutritional counseling.

  Most often, this multifaceted approach requires a team of health care providers that may include a doctor, nurse, rehabilitation specialist, dietitian and social worker. Programs can vary widely, however. Your doctor can usually tell you about pulmonary rehabilitation programs in your area. Or contact the American Lung Association at 800-LUNGUSA (800-586-4872) for more information.

• Lung transplantation. This may be an option for people with severe interstitial lung disease who aren't likely to benefit from other treatment options.

  In order to be considered for a transplant, you must agree to quit smoking if you smoke, be healthy enough to undergo surgery and post-transplant treatments, be willing and able to follow the medical program outlined by the rehabilitation and transplant team, and have the patience and emotional strength and support to undergo the wait for a donor organ. The last is particularly important because donor organs are in short supply.

Being involved in your own treatment and staying as healthy as possible are essential to living with interstitial lung disease. Take these steps to benefit your health:

• Stop smoking. There is an association between smoking and some types of idiopathic interstitial lung disease, the most severe and potentially lethal form of the disorder. Talk to your doctor about options for quitting, including smoking cessation programs, which use a variety of proven techniques to help people quit.
• Enroll in a pulmonary rehabilitation program. These programs vary widely, but in general they focus on improving your ability to exercise and carry out normal activities, managing shortness of breath with breathing techniques, improving your appetite and nutritional status, dealing with the difficult psychological aspects of living with lung disease, and improving overall quality of life.
• Exercise regularly, as prescribed by your doctor. Exercise is a double-edged sword for people with lung disease; it requires an increased intake of oxygen, and it makes symptoms worse. At the same time, exercise is essential for maintaining lung function, reducing stress and depression, and maintaining overall health and well-being. Ask your doctor for a referral to a pulmonary rehabilitation program before you start or resume exercising.

• Eat well. People with lung disease may lose weight both because it's uncomfortable to eat and because of the extra energy it takes to breathe. Yet a nutritionally rich diet that contains adequate calories is essential. The type of food you eat, the time of day you eat and the size of portions can all play a role in getting the nourishment you need.

  Because it's often easier to breathe when your stomach isn't completely full, you may want to eat smaller meals throughout the day rather than two or three large ones. You might also try choosing lighter fare, such as fruit and salads, rather than rich or fatty foods, which take more energy to digest. A dietitian can give you further guidelines for healthy eating.

  If you're overweight, losing weight to achieve a healthy body mass index (BMI) can have dramatic effect on your ability to breathe and your exercise tolerance.

Living with a chronic lung disease is emotionally and physically challenging. Your daily routines and activities may need to be adjusted, sometimes radically, as breathing problems worsen or health care needs take priority in your life. Feelings of fear, anger and sadness are normal as you grieve for the loss of your old life and worry about what's next for you and your family.

These suggestions may help you cope with interstitial lung disease:

• Share your feelings with your loved ones and your doctor. Talking openly may help you and your loved ones cope with the emotional challenges of your disease. In addition, clear communication will help you and your family plan effectively for your needs if your disease progresses.
• Consider joining a support group. In a support group, you'll be with people who are facing challenges similar to yours. Group members may share coping strategies, exchange information about new treatment, or simply listen as you express your feelings. If a group isn't for you, you may wish to talk with a mental health provider or clergy member.

Ask your doctor about self-help groups or therapists in your community. Your local health department, public library, telephone book and the Internet also may be good sources for finding a support group in your area.