Formerly known as the idiopathic form of bronchiolitis obliterans organizing pneumonia (BOOP), cryptogenic organizing pneumonia (COP) is a diffuse interstitial lung disease affecting distal and respiratory bronchioles and alveolar ducts and walls. It usually presents in patients aged 50-60 years, with men and women equally affected, and is frequently heralded by a flu-like illness.

Patients typically present with relatively short duration of symptoms (weeks to months) including a persistent nonproductive cough, dyspnea, fever, malaise, weight loss, and occasionally other influenza-like symptoms (nasal congestion, headache, chills and sweats, sore throat, myalgia). Hemoptysis is uncommon. Physical examination reveals inspiratory crackles in a majority of patients, and radiographic findings include peripheral, patchy bilateral opacities.

History of stigmata of extrapulmonary connective tissue disease and/or medication exposure should be sought to differentiate COP from other idiopathic interstitial pneumonitides.