Cryptogenic organizing pneumonitis

Cryptogenic Organising Pneumonitis (COP) or Bronchiolitis Obliterans Organizing Pneumonia (BOOP) is a rapidly developing pneumonia-like illness characterised by lung inflammation and scarring that obstruct the small airways and air sacs of the lungs (alveoli). Its name is derived from the fact that it closely mimics pneumonia infections. (The term COP is used in Europe and BOOP in North America.)

Epidemiology
Reported incidence is 0.01%, but COP may be more common and underdiagnosed. It usually begins between the ages of 40 and 60 and affects men and women equally. The mortality rate is approximately 7%, although these tend to be the elderly or those in poor health from other conditions.

Etiology
COP/BOOP may be triggered by infections from bacteria, viruses and parasites, drugs, or toxic fumes. It was identified in 1985, although its symptoms had been noted before but not recognised as a separate lung disease.

Diagnosis
Almost 75% of people have symptoms for less than two 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 40% of patients. Doctors do not find any specific abnormalities on routine laboratory tests or on a physical examination, except for the frequent presence of crackling sounds (called Velcro crackles, they are "drier" and higher pitched than traditional rales) on auscultation. Pulmonary function tests usually show that the amount of air the lungs can hold is below normal. Hypoxemia at rest which is exacerbated with exercise may be present.

The chest x-ray is distinctive with features that appear similar to an extensive pneumonia, with both lungs showing widespread white patches. The white patches may seem to migrate from one area of the lung to another as the disease persists or progresses. Computed Tomography (CT) may be used to confirm the diagnosis. Bronchoscopic lung biopsy can confirm the diagnosis. In some patients, additional tissue may be required and may be obtained surgically.

Treatment
About two thirds of patients recover with corticosteroid therapy. Prednisolone is often administered in Europe and Prednisone in the USA. These two compounds differ by only one functional group and have the same clinical effect. The steroid is initially administered at high doses, typically 50 mg per day tapering down to zero over a 6 month to one year period. If the steroid treatment is halted too quickly the disease may return.