Interstitial lung disease (ILD) is the general term used to describe approximately 200 specific lung diseases. This assortment of diseases vary in their clinical courses and radiologic features, however they do share some commonalities to justify this broad grouping. All interstitial lung diseases cause a widespread scarring of the lung’s interstitium, that is, the space between lung cells as well as the lung cells themselves. As a result, the lungs become fibrotic and inelastic. This pathological state not only prevents the patient with ILD from inhaling properly but also interferes with the passage of oxygen across the air sac (alveoli) into the blood.
When you combine the occurrence of these 200 lung diseases across all patients, ILD affects about 3 to 8 people in 10,000 (while the occurrence of any one of these lung disease types is fairly uncommon). Men are affected slightly more often than women (about 50% more often), which may be due to differences in occupational and environmental exposures. There is also evidence that ILD affects men and women differently.
A Partial List of Interstitial Lung Diseases
* Acute interstitial pneumonitis
* Idiopathic pulmonary fibrosis
* Bronchocentric granulomatosis
* ILD due to collagen vascular disease (several forms)
* Bronchiolitis Obliterans Organizing Pneumonia
* Cryptogenic organizing pneumonia
* Nonspecific interstitial pneumonia
* Desquamative interstitial pneumonia
* Respiratory bronchiolitis
* Eosinophilic granuloma
* Hypersensitivity pneumonia/pneumonitis
* Tuberous sclerosis
Rather than considering the name of each individual lung disease, it is usually more helpful to think about these diseases in terms of their cause. ILD can be caused by a number of different environmental, occupational, medical and genetic insults. In some cases, when the inciting agent can be identified and removed, ILD can be reversed. Often the precise cause of the disease is never clearly identified, unfortunately. These cases are referred to as idiopathic interstitial lung disease.
Several inciting factors of ILD have been identified. Occupational and environmental exposure to one or more agents has been shown in animal models and human patients to lead to ILD. Asbestos, beryllium and crystalline silica dust are some of the inhaled inorganic dusts that can lead to ILD. Any number of organic fumes that occur in various industries can also cause ILD diseases. Certain inhaled proteins from biological sources (pigeons, animal waste or dander, etc.) can act as antigens. These antigens set off an immune attack against the antigen and lung itself.
Some causes of ILD have been linked to pharmaceuticals, both prescribed and illicit, as well as medical therapies. Certain cancer chemotherapeutics are damaging to the lung interstitium and can cause ILD. Radiation exposure, often from directed treatment of cancers in the chest, can spark changes in the lung consistent with ILD. Non-cancer treatments have also been implicated in ILD such as amiodarone, nitrofurantoin, penicillamine, sulfasalazine and tocainide. Recently cholesterol-lowering medications collectively known as statins have been shown to cause ILD in rare instances. Narcotic substances such as crack cocaine and heroin are also believed to lead to ILD. Smoking is a major precipitant of the disease and, while it may or may not be a direct cause, it certainly worsens ILD.
In addition, many illnesses may manifest as a form of ILD. Rheumatic diseases such as scleroderma, systemic lupus erythematosus and rheumatoid arthritis can eventually lead to interstitial fibrosis. Hepatitis C, HIV/AIDS and inflammatory bowel disease have also been associated with ILD.
In rare cases, ILD can be inherited as a component of a genetic disease. For example, patients with neurofibromatosis, Niemann-Pick disease, sarcoidosis or tuberous sclerosis may inherit a type of ILD. If an inherited cause or other insult is not identified, the ILD is classified as idiopathic, which means the cause is unknown.
Despite being caused by over 200 lung diseases, ILD produces a fairly consistent set of clinical symptoms and pathological changes. Shortness of breath is the quite common since the lungs are not able to absorb oxygen sufficiently. Patients often have a dry cough. Since the lungs do not expand properly, the patient struggles to inhale, which leads to chest pain (along with a chronic inflammatory process in the lungs). As air passes through abnormal lung passages, wheezing may occur. As with any chronic lung disease in which oxygenation is compromised, the fingers may exhibit a clinical sign called clubbing. Clubbing is an enlargement and abnormal curving of the tips of the fingers along with changes in the fingernails.
Because these symptoms also occur in much more common diseases like asthma and COPD, often the diagnosis of ILD is not considered early in the disease. It is not known if early identification and intervention would alter the course of the disease, but this may be the case when the inciting agent can be identified and removed early.
ILD tends to get worse gradually and may lead to several complications. While lung tissue is affected by ILD, the blood vessels that carry blood from the heart to the lungs are affected secondarily. This means that the blood pressure in these vessels can increase dramatically, a condition called pulmonary hypertension. These blood vessels are unlike the blood vessels in the rest of body such that patients with pulmonary hypertension may not have high blood pressure systemically. Likewise, the drugs used to treat systemic hypertension do not work well on pulmonary hypertension.
Because of this increased blood pressure in the lung vessels, the right side of the heart is called upon to perform more work. This leads to right heart hypertrophy (abnormal growth) and ultimately right-sided heart failure.
Diagnosis and Treatment of interstitial lung diseases.