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Overview of Idiopathic Interstitial Pneumonias

By Harold R. Collard, MD, Associate Professor, Department of Medicine, University of California San Francisco

Idiopathic interstitial pneumonias are interstitial lung diseases that have no known cause and that affect the lungs similarly.

  • Some types of these pneumonias are much more serious than others.

  • Diagnosis requires chest x-rays, computed tomography, and usually analysis of a sample of lung tissue (biopsy).

The word idiopathic means of unknown cause, so when the cause of interstitial lung disease is not identified, idiopathic interstitial pneumonia is diagnosed. Pneumonias are often thought of as infections, but these diseases do not appear to result from infection.

There are seven types of idiopathic interstitial pneumonias. In decreasing order of frequency, they are

  • Idiopathic pulmonary fibrosis

  • Desquamative interstitial pneumonia

  • Nonspecific interstitial pneumonia

  • Cryptogenic organizing pneumonia

  • Respiratory bronchiolitis-associated interstitial lung disease

  • Lymphoid interstitial pneumonia

  • Acute interstitial pneumonia

All types cause cough and shortness of breath and affect the lungs similarly. The ends of the fingers may become thick or club-shaped (see Figure: Recognizing Finger Clubbing). Through a stethoscope, doctors often hear crackling sounds. Although symptoms may be similar, disorders differ in how quickly symptoms develop, how they are treated, and how serious they are.

Comparing Types Of Idiopathic Interstitial Pneumonias


People Most Often Affected

Percentage of Affected People Who Smoke Cigarettes



Idiopathic pulmonary fibrosis

More frequently, men over 50

More than 60%

Pulmonary rehabilitation

Lung transplantation

Pirfenidone (not available in the United States)

50–70% die in 5 years.

Desquamative interstitial pneumonia

More frequently, men aged 30–50

More than 90%

Smoking cessation


5% die in 5 years.

Nonspecific interstitial pneumonia

More frequently, women aged 40–60

Fewer than 40%


Fewer than 50% die in 5 years.

Cryptogenic organizing pneumonia

People of any age, usually aged 40–50

Fewer than 50%


Two thirds completely recover, but the disorder recurs in many.

Death is rare.

Respiratory bronchiolitis–associated interstitial lung disease

People aged 30–50 (slightly more men)

More than 90%

Smoking cessation


Death is rare.

Lymphoid interstitial pneumonia

Mostly women of any age



The prognosis is difficult to predict.

Acute interstitial pneumonia

People of any age


Best treatment unknown

60% die in less than 6 months.


Chest x-rays are done.Computed tomography (CT) of the chest is done. CT may allow doctors to make a diagnosis. If not, doctors remove a small sample of lung tissue for examination under a microscope (lung biopsy). Usually, biopsy is done surgically with use of a thoracoscope (see Thoracoscopy).

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


Smoking cessation is always recommended because smoking is likely to make the disorder progress more rapidly. Other treatments depend on the type of idiopathic interstitial pneumonia but may include corticosteroids or other drugs.

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* This is the Consumer Version. *