Idiopathic interstitial pneumonias are interstitial lung diseases that have no known cause and that affect the lungs similarly.
The word idiopathic means of unknown cause, so when the cause of interstitial lung disease is not identified, idiopathic interstitial pneumonia is diagnosed. Pneumonias are often thought of as infections, but these diseases do not appear to result from infection.
There are six types of idiopathic interstitial pneumonias. In decreasing order of frequency, they are
Some experts also consider lymphoid interstitial pneumonia to be a type of idiopathic interstitial pneumonia.
All types cause shortness of breath and affect the lungs similarly. However, they differ in how quickly they develop, how they are treated, and how serious they are. For example, most diseases take weeks to months to develop, but idiopathic pulmonary fibrosis takes more than 12 months to fully develop. Acute interstitial pneumonia takes only 1 to 2 weeks.
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Chest x-rays, pulmonary function tests (see see Pulmonary Function Testing (PFT)), and computed tomography (CT) are done. CT may be diagnostic. If not, doctors remove a small sample of lung tissue for examination under a microscope (lung biopsy). Usually, biopsy is done surgically with use of a thoracoscope (see see Thoracoscopy).
Blood tests are usually done. They usually cannot confirm the diagnosis but are done as part of the search for other, similar disorders. Doctors may also order an electrocardiogram (ECG) or echocardiogram to determine whether the heart has been affected by the lung disease.
Idiopathic Pulmonary Fibrosis
Idiopathic pulmonary fibrosis is the most common form of idiopathic interstitial pneumonia.
The lungs suffer progressive injury for a long period of time. The injury causes chronic inflammation that eventually leads to lung scarring (fibrosis).
Symptoms depend on the extent of the lung damage, the rate at which the disease progresses, and whether complications, such as lung infections and right-sided heart failure (cor pulmonale—see see Sidebar 1: Cor Pulmonale: A Disorder Stemming From Pulmonary Hypertension) develop. The main symptoms start insidiously as shortness of breath on exertion, cough, and diminished stamina. Other common complaints include weight loss and fatigue. In most people, symptoms worsen over a period ranging from about 6 months to several years.
As the disease progresses, the level of oxygen in the blood decreases, and the skin may take on a bluish tinge (called cyanosis) and the ends of the fingers may become thick or club-shaped (see Fig. 1: Recognizing Finger Clubbing). Strain on the heart may cause the right ventricle to enlarge, eventually resulting in right-sided heart failure. Through a stethoscope, doctors often hear crackling sounds. These sounds are called Velcro crackles, described as such because the sound is similar to that of Velcro when it is pulled apart.
A chest x-ray may show widespread tiny white lines, often in a netlike pattern, most profuse in the lower parts of both lungs. Computed tomography (CT) typically shows a pattern of patchy, white lines in the lower lungs. In areas of more severe involvement, the thick scarring often creates a honeycombing appearance. Pulmonary function tests (see see Pulmonary Function Testing (PFT)) show that the amount of air the lungs can hold is below normal. Analysis of a blood sample or use of an oximeter (see see Arterial Blood Gas (ABG) Analysis) shows a low level of oxygen with minimal exercise (walking at a normal pace) and, as the disease progresses, even when the person is resting.
To confirm the diagnosis, doctors may do a lung biopsy by using a procedure called bronchoscopy (see see Bronchoscopy). Many times, a larger tissue sample is needed and must be removed surgically, sometimes with use of a thoracoscope (see see Thoracoscopy).
Blood tests cannot confirm the diagnosis but are done as part of the search for other disorders that may cause a similar pattern of inflammation and scarring. For example, doctors do blood tests to screen for certain autoimmune disorders.
Prognosis and Treatment
Most people continue to get worse. On average, people live less than 3 years after diagnosis. A few people survive for more than 5 years after diagnosis. A few die within several months.
If a chest x-ray or lung biopsy shows that scarring is not extensive, the usual treatment is a corticosteroid (such as prednisone), with or without azathioprine, N-acetylcysteine, or both. Doctors evaluate the person's response using chest x-rays, CT, and pulmonary function tests. High doses of prednisone are usually given for about 3 months, and then the dose is gradually reduced over another 3 months. Much lower doses are then continued for 6 more months. However, this combination treatment fails to help most people. Promising treatments that appear to decrease lung fibrosis and prolong survival include pirfenidone and bosentan.
Other treatments are aimed at relieving symptoms: pulmonary rehabilitation for improving ability to carry out activities of daily life (see see Overview of Pulmonary Rehabilitation), oxygen therapy for low blood oxygen levels, antibiotics for infection, and drugs for the heart failure that is produced by cor pulmonale. Lung transplantation (often with a single lung) has been successful in some people with severe idiopathic pulmonary fibrosis.
Respiratory Bronchiolitis–Associated Interstitial Lung Disease and Desquamative Interstitial Pneumonia
Respiratory bronchiolitis-associated interstitial lung disease and desquamative interstitial pneumonia are rare conditions that cause chronic lung inflammation and occur mostly in current or former cigarette smokers.
These conditions have many similarities, so that some experts think they may be part of the same disorder. However, desquamative interstitial pneumonia is often more severe. Both disorders affect cigarette smokers in their 30s and 40s, with most people developing shortness of breath with even minimal exertion. Men are affected more often than women (ratio of almost 2:1).
A chest x-ray shows less severe changes than in idiopathic pulmonary fibrosis and may show no changes in up to 20% of people. Pulmonary function tests show a decline in the amount of air contained in the lungs. The amount of oxygen in a blood sample is low.
A lung biopsy is often needed to confirm the diagnosis.
About 70% of people who have respiratory bronchiolitis-associated interstitial lung disease or desquamative interstitial pneumonia survive for 10 years or longer. The response is even better when people stop smoking.
Some doctors give corticosteroids because they may be effective in other interstitial lung diseases, but the effectiveness is unknown.
Cryptogenic Organizing Pneumonia
Cryptogenic organizing pneumonia (also called bronchiolitis obliterans organizing pneumonia) is a rapidly developing idiopathic interstitial pneumonia characterized by lung inflammation and scarring that obstructs the small airways and air sacs of the lungs (alveoli).
The disease usually begins between the ages of 40 and 60 and affects men and women equally. Cigarette smoking does not appear to increase the risk of developing the disease.
Almost 75% of people have symptoms for less than 2 months before seeking medical attention. A flu-like illness, with a cough, fever, a feeling of illness (malaise), fatigue, and weight loss, heralds the onset in about 50% of people.
Diagnosis and Treatment
Doctors do not find any specific abnormalities on routine laboratory tests or on a physical examination, except for the frequent presence of crackling sounds (called Velcro crackles) when the doctor listens with a stethoscope. Pulmonary function tests usually show that the amount of air the lungs can hold is below normal. The amount of oxygen in the blood is often low at rest and is even lower with exercise.
The chest x-ray is distinctive with features that appear similar to an extensive pneumonia, with both lungs showing widespread white patches. The white patches may seem to migrate from one area of the lung to another as the disease persists or progresses. Computed tomography (CT) may be used and sometimes confirms the diagnosis. Often, the findings are typical enough to allow doctors to make a diagnosis without ordering additional tests.
In other cases, to confirm the diagnosis, doctors do a lung biopsy using a bronchoscope (see see Bronchoscopy). Many times, a larger sample is needed and must be removed surgically.
When treated with corticosteroids, about two thirds of people recover. However, symptoms may later return. If so, repeat treatment with corticosteroids is usually effective.
Nonspecific Interstitial Pneumonia
Nonspecific interstitial pneumonia is an idiopathic interstitial pneumonia that occurs mainly in women, people who do not smoke, and people younger than 50 years.
Nonspecific interstitial pneumonia seems to be the second most common kind of idiopathic interstitial pneumonia. Most people are between the ages of 40 and 50. Most people have no known cause or risk factor. However, a similar process can develop in people with connective tissue disorders (in particular, systemic sclerosis and polymyositis or dermatomyositis), in some forms of drug-induced lung injury, and in people with hypersensitivity pneumonitis (see see Hypersensitivity Pneumonitis).
A dry cough and shortness of breath develop over 6 to 18 months. Low-grade fever and a feeling of illness (malaise) may occur, but high fever, weight loss, and other general symptoms of illness are unusual.
Diagnosis and Treatment
As with other idiopathic interstitial pneumonias, chest x-rays are done, and CT is usually also done. Pulmonary function tests usually show that the amount of air the lungs can hold is below normal. The amount of oxygen in the blood is often low at rest and is even lower with exercise. Doctors often do bronchoscopy (see see Bronchoscopy) and wash segments of the lung with a salt-water solution and then collect the washings (bronchoalveolar lavage) for testing. More than half of people have more lymphocytes (a type of white blood cell) than normal in the washings. Lung biopsy is often necessary.
Corticosteroids are usually effective. More than 80% of people survive for more than 10 years after being diagnosed.
Acute Interstitial Pneumonia
Acute interstitial pneumonia (also called accelerated interstitial pneumonia or Hamman-Rich syndrome) is an idiopathic interstitial pneumonia that develops suddenly and is severe.
Acute interstitial pneumonia causes the same type of symptoms as the acute respiratory distress syndrome (see see Acute Respiratory Distress Syndrome (ARDS)). It tends to affect healthy men and women who are usually older than 40. Fever, cough, and difficulty breathing develop over 1 to 2 weeks, typically progressing to acute respiratory failure.
When possible, the diagnosis is confirmed with CT, lung biopsy, and pulmonary function tests.
Treatment aims to keep the person alive until the disorder resolves. Mechanical ventilation is needed if there is respiratory failure. Corticosteroids are generally used, but it is not clear whether they are effective.
More than 60% of affected people die within 6 months, usually from respiratory failure. In people who survive, lung function usually improves with time. However, the disease may recur.
Last full review/revision March 2008 by Talmadge E. King, Jr., MD