ASTHMA & RESPIRATORY SYSTEM Emphysema • Bronchitis • Pneumonia • Pleurisy • Sarcoidosis • Cystic fibrosis • Emphysema • Respiratory syncytial virus • Pulmonary embolism • Bronchiolitis • Asbestosis • Interstitial lung disease

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More than 100 conditions make up the group of disorders called interstitial lung disease. Most of them cause progressive scarring of lung tissue that eventually affects your ability to breathe and obtain enough oxygen, but beyond this, the disorders vary greatly.

Although the majority of cases of interstitial lung disease develop gradually with few warning signs, a few come on suddenly. Some are more common in men than in women, but a few affect women exclusively. And although doctors can pinpoint why some cases of interstitial lung disease occur, most have no known cause.

In all cases, lung scarring, once it occurs, is generally irreversible. Corticosteroid drugs, the most common treatment, 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 of them still in the experimental stage, may eventually prove more effective than steroids.

Despite the wide variety of disorders classified as interstitial lung disease, the signs and symptoms are often remarkably similar:

• A feeling of breathlessness (dyspnea), especially during or after physical activities
• A dry cough

Because these problems are vague and tend to develop gradually — often long after you have irreversible lung damage — you may attribute them to aging, to being overweight or out of shape, or to the residual effects of an upper respiratory infection.

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

Other, far less common signs and symptoms of some types of interstitial lung disease include wheezing, unintended weight loss and clubbing of the fingers, which occurs when your fingertips painlessly enlarge and the nails curve over the tops of your fingertips.

Each time you inhale, air travels to your lungs through two major airways called bronchi. Inside your lungs, the bronchi subdivide like the roots of a tree into a million smaller airways (bronchioles) that finally end in clusters of tiny air sacs (alveoli) — about 300 million in each lung. 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.

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 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 dry sponge, which makes it more difficult to breathe and harder for oxygen to enter your bloodstream.

Scarring in interstitial lung disease seems to occur when an injury to your lungs triggers an abnormal healing response. Ordinarily, your body generates 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 precipitating factors include:

• Infections. These include viral infections such as cytomegalovirus, a particular problem for people with compromised immune systems; bacterial infections, including pneumonia; fungal infections such as histoplasmosis; and parasitic infections.
• Occupation 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 (silicosis), asbestos fibers (asbestosis) or hard metal dust are especially at risk of debilitating lung disease. So are people exposed to certain chemical fumes — sulfuric acid, for example — 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 dust, sugar cane, and 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.
• Radiation. A small percentage of people who receive radiation therapy for lung or breast cancer show signs of lung damage months or sometimes years after the initial treatment. The severity of the damage depends on how much of the lung is exposed to radiation, the total amount of radiation administered, whether chemotherapy also is used and the presence of underlying lung disease.
• Drugs. Nearly 50 drugs can damage the interstitium of the lungs, especially 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 involve systemic processes that affect tissue throughout the body. Among these are connective tissue disorders and hematological diseases, including systemic lupus erythematosis, rheumatoid arthritis, dermatomyositis, polymyositis, Sjogren's syndrome and sarcoidoisis.

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

Usual interstitial pneumonitis is the most prevalent of the idiopathic interstitial lung diseases. Accounting for more than half of all cases, it's so common that the terms "usual interstitial pneumonitis" and "idiopathic pulmonary fibrosis" are often used interchangeably. 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 twice as many men as women and usually develops between the ages of 40 and 70.

Although the names are nearly identical, pneumonitis is not the same as pneumonia. Pneumonitis is lung inflammation without infection, whereas pneumonia is lung inflammation that results from infection. In addition, pneumonia is generally limited to one or two areas of the lungs, but pneumonitis involves all five lobes — two in the left lung and three in the right.

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 and acute interstitial pneumonitis.

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

• Age. Although infants and children occasionally develop interstitial lung disease, the disorder is much more likely to affect adults. Idiopathic forms of the disease usually develop between the ages of 40 and 70.
• Your sex. Given the wide range of disorders classified as interstitial lung disease, it's hard to say definitively whether the disease affects one sex more than the other. But there are a few notable exceptions. Lymphangioleiomyomatosis, for example, a rare disorder in which muscle cells invade and eventually obstruct the airways and blood and lymph vessels in the lungs, affects only women of childbearing age. And lung diseases resulting from exposure to occupational toxins are much more common in men than they are in women.
• 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.

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. Far more smokers and former smokers develop idiopathic interstitial lung diseases than do people who have never smoked. The risk seems to increase with the number of years and the number of cigarettes smoked.
• 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 but symptoms tend to appear at a younger age.Although research is being done on familial pulmonary fibrosis, researchers haven't yet identified the genes that may be involved. They have, however, discovered genetic alterations in surfactant proteins — substances in the airways and air sacs that protect the lungs and help them function normally — in people with other forms of idiopathic pulmonary fibrosis.
• Gastroesophageal reflux disease (GERD). Researchers are investigating a possible link between idiopathic interstitial lung disease and gastroesophageal reflux disease, which occurs when stomach acid or, occasionally, bile salts back up into your esophagus.

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.

Identifying and determining the cause of interstitial lung disease can be extremely challenging. An unusually large number of disorders, with more than 200 causes, 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, and the nomenclature and classification systems of both have historically been confusing and controversial. 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, doctors normally begin by taking a comprehensive medical history, focusing especially on occupational exposure to lung-damaging toxins, on medications and on the presence of health problems commonly associated with lung disorders.

But although a medical history and physical exam can be useful in ruling out certain conditions, they can't accurately diagnose interstitial lung disease. Instead, doctors normally rely on tests such as:

• Chest x-ray. Although this is often the first test given in cases of suspected lung problems, a chest X-ray can't diagnose 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. This is the gold standard imaging test for interstitial lung disease. Whereas a traditional chest X-ray produces two-dimensional images of your lungs, a computerized tomography scan uses an X-ray-sensing unit and a large computer to create cross-sectional images that are far more detailed. A high-resolution CT 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 in and out of your lungs. As scarring becomes worse, you're able to take less air in and blow less out. This part of the test takes just a few minutes. Full PFTs, which give far more information and take longer, can measure the amount of gases exchanged across the membrane between your alveolar wall and capillary membrane.
• 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 anesthetic. The most common side effects are sore throat and hoarseness that may last a few days. More serious risks include bleeding and collapsed lung (pneumothorax).
• Bronchoalveolar lavage. In this procedure, your doctor injects saltwater (saline) through a bronchoscopeinto 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 diagnosea 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 insertedthrough 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. Because video-assisted thoracoscopic surgery allows a surgeon to make small incisions in your chest wall rather than cut through a rib, you're likely to have less pain and to heal more quickly than you are with traditional open lung surgery. Risks of the procedure include infection, bleeding, an air leak in the lung wall and pneumonia.

Scar tissue formation in your lungs can lead to a series of increasingly serious 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 disrupt your body's basic functioning, and severely low levels can be life-threatening.
• 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 the smallest arteries and capillaries are compressed and obliterated by scar tissue, causing increased resistance to blood flow in your lungs. This in turn raises pressure within the pulmonary arteries. Pulmonary blood pressure can be measured by inserting a small catheter in the right side of the heart or by a noninvasive cardiac echo. Pulmonary hypertension is a serious illness that becomes progressively worse and that eventually may prove fatal.
• Right-sided heart failure (cor pulmonale). This serious condition occurs when your heart's right ventricle — which is less muscular than the left — has to pump harder than usual to move blood through obstructed pulmonary arteries. Initially, your heart tries to compensate for the increased workload by thickening its walls and dilating the chamber of the right ventricle to increase the amount of blood it can hold. But this measure works only temporarily, and eventually the right ventricle fails from the extra strain.
• Respiratory failure. Often the end stage of chronic lung disease, respiratory failure occurs when blood levels of oxygen become dangerously low or, as in the case of emphysema, carbon dioxide levels become excessively high. Severely low blood oxygen can lead to heart arrhythmias and unconsciousness and high carbon dioxide levels to sleepiness and confusion. Eventually, respiratory failure may prove fatal.

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. Treatments include:

• Corticosteroid drugs. Although these anti-inflammatory drugs are the initial treatment of choice, they help only about one in five people with interstitial lung disease. Those most likely to benefit have a nonidiopathic disorder and reversible changes in their lungs. Steroids seldom improve lung function in people with idiopathic pulmonary fibrosis, and when they do, the benefits are usually temporary. In general, you take steroids for several months until symptoms improve and then you slowly taper off the medication. If your symptoms return, your doctor may recommend further steroid therapy or an immunosuppressive drug such as azathioprine. Taken for long periods of time or in large doses, steroids 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.
• Cytotoxic drugs. Azathioprine, which is normally used to prevent organ rejection after a transplant, and the anti-cancer drug cyclophosphamide may be used to treat interstitial lung disease. The drugs are prescribed when steroids fail to improve symptoms or, increasingly, as a first-line treatment in combination with steroids. Cytotoxic drugs can cause severe side effects, including reduced production of red blood cells, skin cancer and lymphoma.
• Antifibrotics. These drugs are used to help reduce the development of scar tissue. In clinical studies, they showed promise for slowing the progression of lung damage without suppressing the immune system, but real-world results have been disappointing.
• 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, prevent or lessencomplications from low blood oxygen levels, and improve your sleep and sense of well-being. It can also reduce blood pressure in the right side of your heart. You're most likely to receive oxygen when you sleep or exercise, although some people may use it around the clock. Children with interstitial lung disease are especially likely to need oxygen therapy.
• 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. To that end, pulmonary rehabilitation programs focus on exercise, on teaching you how to breathe more efficiently, on education, and on 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 for more information.
• Lung transplantation. This may be an option for younger 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 therehabilitation 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. In general, single-lung transplants are more successful in people with interstitial lung disease than double-lung transplants are. And although many people who receive lung transplants enjoy a good quality of life, the survival rate is lower than it is for other types of transplants. What's more, the anti-rejection drugs you must take for life make you more susceptible to infection and can increase your risk of high blood pressure, diabetes and cancer.

Being involved in your own treatment and staying as healthy as possible are essential to living with interstitial lung disease. For that reason, it's important to:

• Stop smoking. A strong association exists between smoking and idiopathic interstitial lung disease, the most severe and potentially lethal of the disorders. Smoking is also implicated in hundreds of other life-threatening conditions, including heart disease and cancers of the mouth, throat, esophagus, lung, bladder, kidney, pancreas, stomach, liver, colon, cervix and breast. Talk to your doctor about options for quitting, including smoking cessation programs, which use a variety of proven techniques to help people quit.
• Exercise regularly. 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, for reducing stress, and for maintaining overall health and well-being. If you're already exercising, don't stop. And if you're not currently physically active, consider starting with a moderate workout, such as riding a stationary bike or walking. For instance, you might begin walking at a comfortable pace for just 10 minutes a day. Once you can walk the entire time without stopping to rest, increase the length of your walk by a minute or two each week. Many people with severe lung disease eventually can walk at least 30 minutes nonstop. If you've been prescribed oxygen for regular use, be sure to use it when you exercise. You might also ask your doctor for a referral to an exercise physiologist, who can design an exercise program specifically for you.
• 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 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.
• 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.