Cryptogenic Organizing Pneumonia: Types, Causes, Symptoms, And Treatment

Pneumonia is a catch-all term for any kind of infection in one or both lungs that lead to inflammation of the air sacs and subsequently, difficulty breathing.

It can be caused by a variety of viruses and bacteria or, less commonly, fungi and thus comes in a number of varieties. However, some forms of pneumonia are not caused by infections at all.

One of these is cryptogenic organizing pneumonia.

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What is Cryptogenic Organizing Pneumonia?

Cryptogenic organizing pneumonia (COP) is a form of interstitial lung disease that causes inflammation of the airways and air sacs in the lungs. It is called cryptogenic because the cause is typically unknown.¹

If you have COP, inflammation is caused not by an infection but by organized swirls of inflammatory tissue. There are other types of organizing pneumonia that have similar symptoms but may be more easily traced to a specific cause or underlying condition. 

These can be caused by hematologic malignant neoplasm, a form of blood cancer, collagen vascular disease, or drug use. This might also be called secondary organizing pneumonia. When there is no underlying condition or traceable cause, it is cryptogenic, although your doctors might have their suspicions as to what caused your condition.²


By definition, the cause of COP is unknown. However, it is believed to be a response to some kind of injury to the lungs. Possible causes thus include:

  • Respiratory infections

  • Radiation therapy

  • Exposure to chemicals

  • Exposure to birds

  • Organ transplantation

  • Medication side effects.

In many cases, the cause of your COP might never be identified. Your risk of COP is higher if you have lung cancer, lymphoma, rheumatoid arthritis, lupus, scleroderma, or another inflammatory condition.


The symptoms of COP may at first appear to be flu-like, but over time they include:

  • Persistent, non-productive cough

  • Weight loss

  • Shortness of breath

  • Fever

  • Chills and shaking

  • Loss of appetite

  • Fatigue

In some rare cases, patients may experience pain in their chest and/or joints, night sweats, or coughing up blood.

Diagnosis and types

COP is typically a diagnosis of exclusion, meaning that it is diagnosed after other causes of your symptoms have been eliminated, such as medication side effects or lung cancer. Typically, various tests will be done to look for other causes, including chest X-rays, blood tests, lung function tests, and possibly, if cancer is suspected, a lung biopsy. Your doctor will also look at your medical history.

If your symptoms come on quickly it might be classed as acute fulminant COP. This can look like ARDS (adult respiratory distress syndrome), and some patients may require invasive mechanical ventilation. This is one of the more serious forms of COP and may result in hospitalization for a fairly extended period of time.

Fibrosing variants of COP result in fibroblast deposits inside the lung and can occasionally present aggressively and cause respiratory failure. For the most part, however, they have the same symptoms.

Differential diagnoses might include secondary organizing pneumonia, which is caused by an underlying condition, a medication, or the abuse of drugs. In this case, your doctor will want to treat the underlying condition, although they may still treat you for the symptoms. If your pneumonia is caused by a medication, you may need to change your dose or switch to an alternative.


Milder versions of COP can self-resolve and thus require no treatments. Most people completely recover, and corticosteroid therapy results in complete recovery in up to 80% of patients within a few weeks to three months.³

The mainstay treatment for COP is corticosteroids, such as prednisone, which aims to reduce inflammation. You may need to take steroids for anywhere from a few weeks to a few months and must take them exactly as prescribed. Prednisone also suppresses the immune system, so you should be very careful to stay away from people who are sick.

In most cases, if prescribed prednisone, you will take it either daily or every other day until you have recovered.

If your pneumonia does not respond to steroids, your doctor might add a cytotoxic drug, such as cyclophosphamide. This drug is normally used to treat cancer but can also work on COP. You should not take cyclophosphamide if you are breastfeeding.

Antibiotics will not help the symptoms of COP as it is not caused by an infection, although it can happen as a sequel to bacterial or viral infection. This makes it important to properly diagnose COP to avoid antibiotic overuse.

Note that there is no standardized treatment for fibrosing COP, which is much more serious and can result in respiratory failure. However, even in these cases, steroids are still the mainstay treatment.

If you have had COP once, you are at higher risk of getting it again and your doctor may recommend careful monitoring so that a relapse can be detected and treated quickly. Stopping your medication before you are instructed to do so increases your chance of a relapse. 

Who is at risk

The primary risk factor for cryptogenic organizing pneumonia is age. Most individuals experience it for the first time in their 50s or 60s. Men and women are affected equally.

Unusually for lung disease, smoking is not considered a risk factor for COP. However, smoking can cause many ailments, and it is always a good idea to quit if you can.

Other known risk factors are:

  • Having had a lung infection recently. Infectious pneumonia can sometimes turn into organizing pneumonia.

  • People who are taking certain drugs, including bleomycin sulfate, methotrexate, certain antibiotics, and minocycline. It is also associated with the illicit use of cocaine or with excessive doses of L-tryptophan.

  • People with certain connective tissue issues such as rheumatoid arthritis, lupus erythematosus, or Sjögren syndrome.

  • Having received a lung transplant.

  • Having received a bone marrow transplant.

  • Having received radiotherapy to the breast.

However, many of these cases are not associated with a known risk factor and appear cryptogenic or idiopathic. Again, the primary risk factor is age, and COP is rarely seen in younger individuals. Pneumonia symptoms in younger people are thus far more likely to be from an infection.

When to see a doctor?

You should always see a doctor if you have symptoms that might be pneumonia. This includes fever, sweating, chills, a persistent cough, and shortness of breath while doing normal activities or resting.

The majority of cases of pneumonia are caused by an infection, and these types of pneumonia are contagious. They are spread by respiratory droplets from sneezing or coughing (except for fungal pneumonia, which is caught from the environment and not passed on from person to person).

Your doctor can determine what kind of pneumonia you have and treat it appropriately. Note that even if you can continue with normal activities, you can still have pneumonia (called "walking pneumonia"), and it still needs to be treated.

The lowdown

COP is a rarer cause of pneumonia symptoms and is often a diagnosis of exclusion. Unifocal COP is sometimes found while investigating cancer, as it can easily be mistaken for a tumor. Most COP cases are treatable with steroids, although they are prone to recurrence.

It is diagnosed primarily by exclusion, although a lung biopsy is sometimes done, especially for COP lesions that may appear to be cancerous on a scan. If you are diagnosed with COP, it is vital to take your medication as directed and finish the course of prednisone even if you are feeling better, as stopping early increases the risk of it coming back.

A few varieties of COP are more acute and serious and can result in hospitalization, but most people make a full recovery when treated properly.

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