Cryptogenic Organizing Pneumonia (COP)

Formerly known as Bronchiolitis Obliterating Organizing Pneumonia (BOOP)


4-to-8-week history of symptoms similar to infectious pneumonia (cough, shortness of breath, fever, chills, weight loss) (1). Generally, suspicion arises when a patient is treated for infectious pneumonia without improvement.


Exact etiology unclear, but involves idiopathic alveolar epithelial injury, creating inflammation, fibroblast proliferation and fibrin band formation (2)


  • Imaging (3)
    • CXR: Diffuse, bilateral, peripherally-distributed opacities
    • HRCT (High-resolution CT): Ground-glass opacities, patchy airspace consolidations, and bronchial wall thickening/dilation, most often worse in the peripheral/lower lung areas
  • Pulmonary Function Tests (4)
    • Restrictive impairment with reduced DLCO and often a reduced FVC and TLC
  • Bronchoscopy with BAL (Bronchoalveolar Lavage) (5)
    • Nonspecific inflammatory pattern (variable increases in lymphocytes, neutrophils, and/or eosinophils). Can decrease the likelihood of eosinophilic pneumonia (if eosinophils low) and infection (if no organisms seen on gram stain or culture)
  • Biopsy (Gold standard for diagnosis, however, in select elderly or ill patients, may be deferred for glucocorticoid trial (6))
    • May be obtained transbronchially via bronchoscopy if the clinical/radiographic presentation is very typical, but typically this is only able to rule out other diseases in the differential diagnosis. Typically, surgical biopsy via VAT (video-assisted thoracoscopy) is preferred to obtain larger pieces of tissue to make the definitive diagnosis (4)
    • Histopathology: Fibroblastic aggregations obstructing alveolar sacs, ducts and bronchioles (7)


  • Corticosteroid therapy, optimum dose/duration not known
  • Guidelines suggest initial doses of 0.75–1 mg/kg, with weaning over 6–12 months (8)


  1. Cryptogenic organizing pneumonia (COP) symptoms, causes and risk factors. Cryptogenic Organizing Pneumonia (COP) Symptoms, Diagnosis and Treatment | American Lung Association. (n.d.). Retrieved November 30, 2021, from 
  2. Chandra, D. (2021, September 18). Cryptogenic organizing pneumonia. StatPearls [Internet]. Retrieved November 30, 2021, from 
  3. Lee, J. (2021, November 17). Cryptogenic organizing pneumonia – pulmonary disorders. Merck Manuals Professional Edition. Retrieved November 30, 2021, from 
  4. Antin-Ozerkis, D. (2019, January 23). Bronchiolitis obliterans organizing pneumonia/cryptogenic organizing pneumonia. Pulmonology Advisor. Retrieved November 30, 2021, from 
  5. Raghu, G., & Meyer, K. C. (2021, September 30). Cryptogenic organising pneumonia: Current understanding of an enigmatic lung disease. European Respiratory Society. Retrieved November 30, 2021, from 
  6. Kewcharoen, J., Poonsombudlert, K., Sathirareuangchai, S., Sae-Ow, W., La, H., & Sriratanaviriyakul, N. (n.d.). Cryptogenic Organizing Pneumonia with a Rare Radiographic Presentation of a Diffuse Micronodular Pattern Mimicking Miliary Lung Infiltration: A Case Report and Review of the Literature. Hindawi: Case Reports in Pulmonology. Retrieved November 30, 2021, from 
  7. Yoshikawa, A., Bychkov, A., & Sathirareuangchai, S. (n.d.). Cryptogenic organizing pneumonia. Pathology Outlines – Cryptogenic organizing pneumonia. Retrieved November 30, 2021, from 
  8. Wells, A. U., & Hirani, N. (n.d.). Interstitial lung disease guideline: The British … – thorax. Interstitial lung disease guideline. Retrieved November 30, 2021, from 

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