Interstitial Lung Disease (Interstitial Pneumonitis)

• Interstitial lung disease includes a group of diseases that have thickening of the supporting tissues between the air sacs of the lungs. This thickening can be due to a variety of causes such as:
  • Associated autoimmune or collagen vascular diseases
  • Exposure to medications or toxins such as asbestos, tobacco smoke, or environmental toxins
  • Associated genetic diseases
  • The cause is not known (idiopathic).
  • The most common symptoms of interstitial lung disease are a dry cough and shortness of breath.
• The diagnosis of interstitial lung disease typically involves imaging tests, measurement of blood oxygen levels, and sometimes, biopsies or tissue sampling.
• Some forms of interstitial lung disease lead to irreversible scarring and respiratory failure.
• Treatment can involve corticosteroid medications to reduce inflammation.
• The prognosis of interstitial lung disease depends on the precise cause.
• Some cases of interstitial lung disease do not have an identifiable cause and are referred to as idiopathic.

Interstitial lung disease includes a group of diseases that have thickening of the supporting tissues between the air sacs of the lungs as the common factor. The interstitium is a thin layer of tissue that is normally appears as a fine lace on X-rays or imaging studies (best visualized as the appearance of a sponge).

Interstitial lung disease results from a variety of causes that lead to thickening of the supporting tissue around the air sacs rather than the air sacs themselves. Interstitial lung disease usually involves all of the lungs diffusely rather than affecting only one area.

Disease of the interstitium is recognized on imaging studies as a thick lace (sponge), sometimes symmetric, and in other types, scattered and irregular.

Several terms related to interstitial lung disease have been used to describe this condition, including "interstitial pneumonia." However, since "pneumonia" is usually associated with an infection, some doctors choose to use the term "interstitial pneumonitis" to refer to inflammation in the interstitial space since many of the causes of this inflammation are not infections. "Interstitial fibrosis" is the term used to refer to the scarring of the lungs that can result from prolonged interstitial inflammation. Interstitial lung disease can be acute (coming on suddenly) or chronic (occurring over time).

Symptoms and signs of interstitial lung disease occur because the damage to the interstitium of the lung impairs breathing function.

The two most common symptoms are shortness of breath and a dry (not producing sputum) cough. These symptoms tend to come on gradually and progress.

Interstitial lung disease that has been present for a long time may cause signs and symptoms related to lowering of the oxygen levels in the blood, such as clubbing of the fingertips and enlargement of the heart.

The symptoms can also reflect the underlying disease process and assist in making a diagnosis. Fevers, fatigue, and weight loss are non-specific, but can suggest an infectious process. It is often difficult to make a diagnosis from symptoms alone, since so many lung diseases can present with shortness of breath and cough.

Interstitial lung disease has a broad list of causes. The exact cause of interstitial lung disease is not always known (idiopathic). Some of the known common causes include toxins, environmental factors, chronic diseases, cancer, and infections. Depending on the cause, interstitial lung disease can resolve or may lead to irreversible scarring and damage to the lungs.

Known causes of interstitial lung disease include the following:

• Environmental factors, such as toxins like asbestos, mold, certain metals, silica dust, talc, grain dust, or bird droppings; interstitial disease caused by some of these irritants is referred to as "hypersensitivity pneumonitis"
• Radiation therapy to the chest
• Certain medications, including some chemotherapy (cancer-fighting) medications and the heart medication amiodarone (Cordarone)
• Chronic autoimmune diseases like rheumatoid arthritis, scleroderma, and lupus
• Infections: One of the more common infectious cause of interstitial inflammation is the bacterium Mycoplasma pneumoniae. Viruses, bacteria, and fungi can all cause interstitial inflammation.
• Cancer in some cases spreads throughout the lymph system in the lungs and appears as interstitial disease
• Congestive heart failure, renal failure both can present with similar findings due to excess fluid in the spongy tissue of the lung

Examples of idiopathic (unknown causes) forms of interstitial lung disease include:

• Bronchiolitis obliterans with organizing pneumonia (BOOP), sometimes known as cryptogenic organizing pneumonia (COP)
• Usual interstitial pneumonitis (UIP)
• Lymphocytic interstitial pneumonitis (LIP)
• Desquamative interstitial pneumonitis (DIP)
• Sarcoidosis
• Lymphangiomyomatosis
• Langerhans cell histiocytosis

The distinction among these idiopathic conditions is based on the exact pattern of lung damage, severity, and location of the disease.

The typical symptoms and signs of interstitial lung disease, when they occur, should prompt a diagnostic work-up that includes a thorough medical history and physical examination, including blood tests to examine electrolyte levels and blood cells counts. There is such a wide variety of causes of interstitial lung disease that besides imaging studies, pulmonary function tests, a few blood tests, and often biopsy, other testing should be specific to the findings of a good history and physical.

A history of exposures to environmental toxins may be explored if there is no apparent cause of the symptoms. Often, the precise diagnosis comes from the history if extensive occupational, vocational, travel, and exposure history is obtained. For example, if a patient has signs and symptoms of a progressive cough and shortness of breath with radiologic findings of diffuse interstitial disease and enjoys raising and caring for pigeons, the likely diagnosis would be hypersensitivity pneumonitis (so called "pigeon breeders lung").

The precise diagnosis of interstitial lung disease may require more specific testing that can include imaging studies or tissue sampling. These rarely give a definitive diagnosis. Diagnostic studies that may be useful are:

• Imaging studies of the chest and lungs are often performed early in the process, when symptoms are apparent. Both chest X-rays and high resolution CT scans of the chest may be ordered. Depending on the history and exam, other testing may be beneficial. For instance, a patient may have arthritic complaints consistent with Rheumatoid arthritis. X-rays of the effected joints may be helpful. Echocardiogram is a test that can evaluate cardiac function as well as the pressures in the lung. This can be useful both for diagnosis and treatment.
• Sometimes blood tests can aid in the diagnosis and or treatment of these patients. Tests for collagen vascular disease (lupus, rheumatoid arthritis), arterial blood gases, liver tests, and others may be beneficial.
• Noninvasive tests that measure lung function are known as pulmonary function tests (PFTs). The most common of these involves forcefully exhaling into a tube, on a device known as a spirometer, to measure lung volume and air flow. These PFTs are usually supplemented with more elaborate testing involving a device known as a body box. This helps measure more accurately the different lung volumes but also can measure gas exchange through the tissue of the lung (diffusing capacity or DLCO).
• Bronchoscopy is the direct visualization and examination of the airways of the lungs using a viewing tube. Biopsies (tissue samples) or washings of the airways are often obtained during this procedure for examination in the laboratory. Usually this does not get an accurate or definitive diagnosis, though it can be helpful to evaluate the possibility of infections, cancer, and sarcoidosis.
• Open lung biopsy is generally necessary if history and less invasive tests are non-diagnostic.

In most major centers, this biopsy is performed by minimally invasive techniques referred to as video assisted thoracic surgery (VATS). This usually only requires a brief hospital stay, sometimes less than 24 hours.

The treatment of interstitial lung disease depends upon the cause. Definitive diagnosis is often essential since the treatment may involve:

• antimicrobial agents,
• immunosuppressing agents,
• avoidance behavior,
• chemotherapy, and
• in some, no therapy is available.

Antibiotics may be given if a bacterial infection is responsible for the condition. Management of the underlying disease process is also essential in a person with interstitial lung disease related to these conditions. If the disease is thought to involve hypersensitivity, then the best therapy is avoidance of this offending substance.

Depending upon the severity of the symptoms, respiratory support, including supplemental oxygen and even ventilator support, may be required. Respiratory therapists may be part of a treatment team with the goal of improving day to day function. Smoking cessation is an essential part of the treatment for anyone with interstitial lung disease.

Corticosteroids are sometimes used in an attempt to control the interstitial inflammation. Drugs that modulate immune function, like azathioprine (Imuran), cyclophosphamide (Cytoxan), mycophenolate (Cellcept) may be given along with or following steroid treatment. These medications may help slow the progression of the disease, but they are unable to reverse the scarring in cases of long-standing interstitial lung disease. In severe cases with irreversible damage, lung transplantation may be indicated.

The disease of idiopathic pulmonary fibrosis does not respond to any measures. The diagnosis can be made at times by the history, physical and characteristic chest CT findings. Sometimes lung biopsy can be avoided if the patient's signs and symptoms present in the classic fashion. If this disease is strongly suspected or diagnosed referral to a tertiary center for transplant center is recommended for evaluation and possible therapeutic research trials.

As mentioned previously, some forms of interstitial lung disease resolve completely, while others lead to long-term and irreversible scarring and lung damage with accompanying respiratory failure . Pulmonary hypertension is a form of high blood pressure that affects the arteries within the lungs. This form of hypertension can develop in cases of long-standing interstitial lung disease and can lead to enlargement of the heart and right-sided (the side of the heart that pumps blood back to the lungs to receive oxygen) heart failure (known as cor pulmonale). The prognosis is dependent upon the type and severity of interstitial lung disease as well as the underlying health status of the patient.

Interstitial lung disease can be prevented only to the extent that its individual causes may be prevented. For example, avoidance of known environmental toxins can help prevent lung damage from these exposures.