Interstitial lung disease (also called diffuse parenchymal or infiltrative lung disease) is a term used to describe a number of different disorders that affect the interstitial space. The interstitial space consists of the air sacs of the lungs (alveoli), the walls of alveoli, and the spaces around blood vessels and small airways. Interstitial lung diseases result in abnormal accumulation of inflammatory cells in lung tissue, cause shortness of breath and cough, and have similarities in their appearances on imaging studies but are otherwise unrelated. Some of these diseases are very unusual.

Early in the course of these diseases, white blood cells, macrophages, and protein-rich fluid accumulate in the interstitial space, causing inflammation. If the inflammation persists, scarring (fibrosis) may replace the normal lung tissue. As alveoli are progressively destroyed, thick-walled cysts (called honeycombing because they resemble the cells of a beehive) are left in their place. The condition resulting from these changes is called pulmonary fibrosis.

Although the various interstitial lung diseases are separate and have different causes, they have some similar features. All lead to a decreased ability to transfer oxygen to the blood, and all cause stiffening and shrinkage of the lungs, which makes breathing difficult and causes cough. However, the elimination of carbon dioxide from the blood is usually not a problem.

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Unusual Interstitial Lung Diseases Disorder Symptoms Treatment Comments Drug-induced interstitial lung disease Slow-developing (over weeks to months) or sudden, severe symptoms Shortness of breath Cough Stopping the drug that is causing symptoms Corticosteroids (sometimes effective) Many classes of drugs may cause this disease. The disease is often more severe in older people. The effects of some drugs on the lung are similar to those of systemic lupus erythematosus (lupus). The extent and severity of the disease are sometimes related to how large the drug dose was and how long the drug was taken. Alveolar hemorrhage syndromes (iron in the lungs) Most commonly, coughing up blood (hemoptysis) Anemia due to chronic blood loss Kidney failure (sometimes) Corticosteroids and cytotoxic drugs (such as azathioprineSome Trade Names IMURAN ) during flare-ups Blood transfusions if needed because of blood loss Oxygen therapy for a low level of oxygen in the blood In this rare disorder, blood leaks from the capillaries into the lungs for unknown reasons. People may also have Goodpasture's syndrome, Wegener's granulomatosis, systemic lupus erythematosus, idiopathic pulmonary hemosiderosis, or drug reactions. Massive bleeding can cause death. Lymphangiomyomatosis Difficulty breathing Cough Chest pain Sometimes coughing up blood Lung transplantation This rare disorder occurs in young women. It may worsen during pregnancy.

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Causes of Interstitial Lung Diseases Type Examples Autoimmune disorders Ankylosing spondylitis, Behçet's syndrome, Goodpasture's syndrome, mixed connective tissue disease, polymyositis and dermatomyositis, relapsing polychondritis, rheumatoid arthritis, scleroderma, Sjögren's syndrome, and systemic lupus erythematosus (lupus) Infections Fungal, mycoplasmal (a type of bacterial), parasitic, rickettsial, or viral infections and tuberculosis Organic dust Bird droppings and molds Drugs AmiodaroneSome Trade Names CORDARONE , bleomycinSome Trade Names BLENOXANE , busulfanSome Trade Names MYLERAN , carbamazepineSome Trade Names TEGRETOL , chlorambucilSome Trade Names LEUKERAN , cocaine, cyclophosphamideSome Trade Names LYOPHILIZED CYTOXAN , goldSome Trade Names See Auranofin , methotrexateSome Trade Names TREXALL , nitrofurantoinSome Trade Names FURADANTIN MACRODANTIN , sulfasalazineSome Trade Names AZULFIDINE , and sulfonamides Gases, fumes, and vapors Chlorine and sulfur dioxide Therapeutic or industrial radiation Radiation therapy for cancer Idiopathic* interstitial pneumonias Acute interstitial pneumonia, cryptogenic organizing pneumonia, desquamative interstitial pneumonia, idiopathic pulmonary fibrosis, lymphoid interstitial pneumonia, nonspecific interstitial pneumonia, and respiratory bronchiolitis-associated interstitial lung disease Other disorders Alveolar proteinosis, amyloidosis, chronic gastric microaspiration, lymphangiomyomatosis, neurofibromatosis, pulmonary Langerhans' cell granulomatosis (histiocytosis), sarcoidosis, and vasculitic disorders (which cause inflammation of blood vessels) such as Churg-Strauss syndrome and Wegener's granulomatosis * Idiopathic means with no known cause.

Diagnosis

Because interstitial lung diseases cause symptoms that are similar to those of much more common disorders (for example, pneumonia, chronic obstructive pulmonary disease), they may not be suspected at first. When interstitial lung disease is suspected, diagnostic testing is done. Testing can vary by the disease suspected but tends to be similar. Most people have a chest x-ray, computed tomography (CT), pulmonary function tests (see Diagnosis of Lung Disorders: Pulmonary Function Testing (PFT)), and often arterial blood gas analysis. CT is more sensitive than chest x-ray and helps doctors make a more specific diagnosis. CT is done using techniques that maximize resolution (high-resolution CT). Pulmonary function tests often show that the volume of air that the lungs can hold is abnormally small. In addition, the person's response to exercise is commonly tested.

To confirm the diagnosis, doctors may remove a small sample of lung tissue for microscopic examination (lung biopsy) using a procedure called fiberoptic bronchoscopy. A lung biopsy done this way is called transbronchial lung biopsy (see Diagnosis of Lung Disorders: Bronchoscopy). Many times, a larger tissue sample is needed and must be removed surgically, sometimes with use of a thoracoscope (a procedure called video-assisted thoracoscopic lung biopsy).

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 electrocardiography (ECG) or echocardiography to determine whether the heart has been affected by the lung disease.

Last full review/revision March 2008 by Talmadge E. King, Jr., MD