Interstitial lung disease
Interstitial lung disease (ILD) refers to a group of diseases characterized by thickening and scarring of the interstitium, the tissue and space between the air sacs. As the interstitium progressively thickens, the lungs become stiffer and less efficient, creating a variety of respiratory symptoms. The scarring and lung stiffness associated with interstitial lung disease is generally irreversible, though medications may slow this process, and pulmonary rehabilitation may help to improve breathing capacity and quality of life.
Definition & Facts
The interstitium is a collection of support structures in the lung, including the membranes that support the air sacs and capillaries, and the space around these structures. Interstitial tissues protect and support the capillaries and lymphatic organs in the lungs. There are many reasons why the interstitium may scar and thicken.
There are over 130 different types of ILD. These diseases are chronic and progressive in nature, non-malignant (unrelated to tumor growth) and non-infectious (unable to be transmitted to others). According to one study, 80.9 per 100,000 men and 67.2 per 100,000 women suffer from ILD in the United States.
Symptoms & Complaints
People with ILD may first notice this shortness of breath while doing household chores, or even just walking up the stairs in their home or putting on clothes. ILD may progress to the point where individuals feel short of breath even at rest, feeling as if they can’t take in enough air in a normal breath. This can lead to chronic fatigue.
Because ILD can occur when people reach middle age, it may be perceived as simply not having as much energy as a younger person. However, breathlessness is a symptom of an underlying, serious disease and should prompt a visit to a physician. Another symptom of ILD is a dry, non-productive cough (not producing mucus) that doesn’t go away. ILD patients may also experience nail clubbing, in which the fingernails and toenails feel like they’re coming loose, turning soft, and changing shape.
ILD refers to a disease process (the thickening and scarring of the interstitium) and there are many causes of this process. Common among these causes is an initial injury or irritation of the lungs triggering an abnormal healing process which includes thickening and scarring of the interstitium. Inhalation of environmental toxicants may be one cause of this process, as in the disease asbestosis which is caused by breathing asbestos. Other toxic substances that can provoke ILD include silica and coal dust such as in silicosis. In addition, mold and bird feathers are two substances which can provoke ILD.
Some drugs can cause ILD. Drugs that treat cardiac arrhythmia, or irregular heartbeat, can cause ILD, as can certain antibiotics and anti-cholesterol drugs. Radiation therapy and chemotherapy can cause ILD. Infections, such as pneumonia and tuberculosis, can cause ILD especially when there is an overly strong immune response to the infection. Some forms of ILD are caused by diseases of connective tissue such as rheumatoid arthritis, and some forms of ILD are idiopathic, which means the cause is unknown.
Diagnosis & Tests
Because ILD has many causes, getting a correct diagnosis can be challenging. Three types of diagnostic tools used to diagnose ILD are imaging tests, pulmonary function tests, and lung tissue analysis. The physician will start by asking questions to assess exposure to irritants including occupational exposure in order to assess the possibility of occupational lung disease and use of any drugs which may cause ILD.
A chest X-ray may show thickened or scarred lung tissue, though on occasion the chest X-ray may be normal even when there is ILD. A high-resolution CT scan can provide information on the severity of lung damage caused by ILD, specifically the density and patterns of scarring.
Pulmonary function tests may be used to assess the extent of breathing problems caused by ILD. One such test includes spirometry which has a patient breathe forcefully into a machine that measures how much air the lungs can hold and how much air can be exhaled from the lungs when breathing. Another test might include pulse oximetry, which is the use of a small device placed on a fingertip that measures oxygen saturation in the blood. Finally, a physician may remove a small amount of lung tissue, or do a direct surgical biopsy of the lungs, to test for ILD.
Treatment & Therapy
Because ILD refers to a process of progressive and irreversible thickening of the interstitium, treatment focuses on slowing this process, rather than curing the disease. Medications may be prescribed to provide temporary improvement of symptoms, while therapies can improve lung function, breathing, and overall quality of life. In the case of medications, the type of medication prescribed depends on the cause of ILD.
When ILD is caused by an immune response to an infection or a disease of connective tissues, immunosuppressants and corticosteroids may be prescribed to slow the disease process and reduce the severity of symptoms. New drugs specific to ILD are currently being tested. One drug, nintedanib, may slow disease progression by interfering with the growth of new scar tissue.
Patients with low levels of oxygen may receive supplemental oxygen when they sleep or exercise, though some may require it all day. Some patients may be referred to pulmonary rehabilitation. Pulmonary therapists help patients practice exercises and breathing techniques. This doesn’t slow disease progression but may help patients continue daily activities and improve quality of life.
Prevention & Prophylaxis
A key factor in the prevention of ILD is avoiding exposure to potential lung irritants. Those who work around harmful substances, like silica dust and coal dust, should consider changing their work environment or wearing protective gear so as to prevent ILD. Those who own birds, or believe there may be mold in their homes, should also consider the potential role these substances may have in the development of ILD. Being vaccinated against common respiratory diseases, like pneumonia and the flu, can also help prevent ILD. Finally, staying active is important to preserving lung function and staying healthy in general.