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Overview of Interstitial Lung Diseases

by Harold R. Collard, MD

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 walls of the air sacs of the lungs (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 appearance 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.

Unusual Interstitial Lung Diseases





Drug-induced interstitial lung disease

Slow-developing (over weeks to months) or sudden, severe symptoms

Shortness of breath


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 lungs 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 (bleeding in the lungs)

Most commonly, coughing up blood (hemoptysis)

Anemia due to chronic blood loss

Kidney failure (sometimes)

Corticosteroids and cytotoxic drugs (such as azathioprine) during flare-ups

Blood transfusions if needed because of blood loss

Oxygen therapy for a low level of oxygen in the blood

In these rare disorders, blood leaks from the capillaries, often because of an autoimmune reaction..

People may also have Goodpasture syndrome, granulomatosis with polyangiitis (formerly called Wegener granulomatosis), systemic lupus erythematosus (lupus), idiopathic pulmonary hemosiderosis (iron in the lungs), or drug reactions.

Massive bleeding can cause death.


Difficulty breathing


Chest pain

Sometimes coughing up blood

Lung transplantation


This rare disorder occurs in young women.

It may worsen during pregnancy.

Types of Interstitial Lung Diseases



Autoimmune disorders

Ankylosing spondylitis (rare), Behçet syndrome (very rare), Goodpasture syndrome, mixed connective tissue disease, polymyositis and dermatomyositis, relapsing polychondritis, rheumatoid arthritis, systemic sclerosis (scleroderma), Sjögren syndrome, and systemic lupus erythematosus (lupus)


Fungal, mycoplasmal (a type of bacterial), parasitic, rickettsial, or viral infections and tuberculosis

Organic dust

Bird droppings and molds


Amiodarone, bleomycin, busulfan, carbamazepine, chlorambucil, cocaine, cyclophosphamide, gold, methotrexate, nitrofurantoin, sulfasalazine, and sulfonamides


Aluminum powder, asbestos, beryllium, metals, sulfur dioxide, talc

Therapeutic or industrial radiation-related

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

Amyloidosis, chronic aspiration, lymphangioleiomyomatosis, neurofibromatosis, pulmonary alveolar proteinosis, pulmonary Langerhans cell granulomatosis (histiocytosis), sarcoidosis, and vasculitic disorders (which cause inflammation of blood vessels) such as eosinophilic granulomatosis with polyangiitis (formerly called Churg-Strauss syndrome) and granulomatosis with polyangiitis (formerly called Wegener granulomatosis)

*Idiopathic means with no known cause.


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 an 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) of the chest, pulmonary function tests (see Pulmonary Function Testing (PFT)), and often arterial blood gas testing. 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. Arterial blood gas tests measure the levels of oxygen and carbon dioxide in the arterial blood and determine the acidity (pH) of the blood.

To confirm the diagnosis, doctors sometimes 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 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 may be done. They usually cannot confirm the diagnosis but are done as part of the search for other, similar disorders.

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