What Is Cryptogenic Organizing Pneumonia?

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Cryptogenic organizing pneumonia (COP)—formerly called bronchiolitis obliterans organizing pneumonia, or BOOP—is a rare interstitial lung disease that affects the distal lung branches (bronchioles) and lung sacs (alveoli).

It is a form of pneumonia in which the bronchioles (small airways), the alveoli (tiny air-exchange sacs), and the walls of the small bronchi become inflamed. 

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In addition to the cryptogenic form, secondary organizing pneumonia can be seen in association with connective tissue diseases, a variety of drugs, malignancy, and other interstitial pneumonias, but the exact incidence (rate of new cases in a specific population over a certain period of time) and prevalence (number of cases in a specific population over a certain period of time) of cryptogenic organizing pneumonia (COP) are unknown.

This article discusses the symptoms, common causes, diagnosis, treatment, and prognosis of COP.


The most common symptoms of COP are:

  • Persistent (lasting two to four months), nonproductive cough (meaning you’re not coughing up mucus)
  • Fever
  • Chills and shaking
  • Shortness of breath
  • Fatigue
  • Loss of appetite
  • Weight loss

Rarely, you may develop:

  • Chest pain
  • Joint aches
  • Night sweats
  • Coughing up blood

Common Causes

COP is idiopathic in nature, meaning that the underlying cause is unknown. Organizing pneumonia is given the diagnosis of COP when, among other characteristics, no definite cause for the organizing pneumonia is found.


COP is a diagnosis of exclusion, which means that all other potential causes must be ruled out before making this diagnosis.

Other causes of organizing pneumonia are:

  • Infections from bacteria, viruses, parasites, or fungi
  • Drugs
  • Radiation therapy side effects (especially in those receiving treatment for breast cancer)

Organizing pneumonia is associated with a number of disorders, including:

  • Certain connective tissue disorders (including the immune system disorders of Sjögren’s syndrome and rheumatoid arthritis)
  • Blood cancers (including lymphoma and acute leukemia)
  • Ulcerative colitis (UC, a form of inflammatory bowel disease that causes inflammation and sores in the inner lining of the large intestine and rectum)

High-resolution computerized tomography (HRCT) and lung biopsy (removing a sample tissue for examination in a lab) are essential to diagnosing COP. Chest X-rays may also be helpful.


The mainstay of treatment for COP is the use of corticosteroids.

Usually, clinical improvement is seen within two weeks. Recurrence is likely so it is important to continue treatment for six to 12 months despite showing signs of improvement. Recurrent disease is generally responsive to additional courses of corticosteroids.

HRCT can be used to track recovery and clinical improvement.


The general short- and long-term outlook for people with COP is good.

COP is rarely fatal. Most people achieve a full recovery after treatment with glucocorticoids.

Still, COP can cause severe lung damage and may require you to stay in the hospital for treatment. In fact, studies show that up to one-third of affected people may experience persistent symptoms and/or abnormalities on pulmonary function testing.


COP is a mysterious condition that damages the lung branches and lung sacs via inflammation. Early and consistent treatment with corticosteroids for six to 12 months usually leads to a full recovery.

A Word From Verywell

COP symptoms vary widely from person to person. If you have mild symptoms you may simply be monitored, and, in some instances, your symptoms may even improve on their own. If they do not, treatment with glucocorticoids—namely corticosteroids—can quickly help your symptoms.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Lung Association. Cryptogenic organizing pneumonia.

  2. U.S. Department of Health and Human Services. Cryptogenic organizing pneumonia.

  3. UpToDate. Cryptogenic organizing pneumonia.

By Shamard Charles, MD, MPH
Shamard Charles, MD, MPH is a public health physician and journalist. He has held positions with major news networks like NBC reporting on health policy, public health initiatives, diversity in medicine, and new developments in health care research and medical treatments.