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Cryptogenic Organizing Pneumonia

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

Cryptogenic organizing pneumonia (also called bronchiolitis obliterans organizing pneumonia) is a rapidly developing idiopathic interstitial pneumonia (see Overview of Idiopathic Interstitial Pneumonias) characterized by lung inflammation and scarring that obstructs the small airways and air sacs of the lungs (alveoli).

The disease usually begins between the ages of 40 and 60 and affects men and women equally. Cigarette smoking does not appear to increase the risk of developing the disease.

Almost 75% of people have symptoms for less than 2 months before seeking medical attention. A flu-like illness, with a cough, fever, a feeling of illness (malaise), fatigue, and weight loss, heralds the onset in about 50% of people.


Doctors do not find any specific abnormalities on routine laboratory tests or on a physical examination, except when doctors listen to the lungs with a stethoscope they frequently hear crackling sounds and occasionally squeaking sounds as the person inhales. Pulmonary function tests (see Pulmonary Function Testing (PFT)) usually show that the amount of air the lungs can hold is below normal. The amount of oxygen in the blood is often low at rest and is even lower during exercise.

A chest x-ray can help doctors make the diagnosis, but it is often not conclusive. Computed tomography (CT) may be done, and sometimes the findings are typical enough to allow doctors to make a diagnosis without ordering additional tests.

In other cases, to confirm the diagnosis, doctors do a lung biopsy using a bronchoscope (see Bronchoscopy). Many times, a larger sample is needed and must be removed surgically.


When treated with corticosteroids, most people recover quickly. However, symptoms may later return, and prolonged treatment is often necessary. If the disease recurs, repeat treatment with corticosteroids is usually effective.

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