Question 13

You are managing a patient with a possible cryptogenic organizing pneumonia (COP). They are receiving a high level of invasive respiratory support.

a.    List five differential diagnosis with similar presentation and imaging findings to COP. (25% marks)

b.    Outline the assessment of suspected COP.
(50% marks)

c.    Discuss the rationale for bronchoalveolar lavage in the diagnosis of COP for this patient. (25% marks)

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College answer

Aim: To explore the challenges of assessment and diagnosis of cryptogenic pneumonias.
Key sources include: A known clinical scenario with important diagnostic ramifications in the ICU. CanMEDS Medical Expert.
Discussion: Some candidates answered parts a) and c) in a reasonably inclusive manner. Many candidates' answers were incomplete or missing. Candidates are encouraged to attempt every part of the question and are reminded there is no negative marking.
Using the assessment structure as outlined in the glossary of terms would have helped candidates focus their answers and avoid incomplete attempts. Candidates who concentrated on bronchoalveolar lavage from a therapeutic perspective did not gain marks, as the question specifically asked for the diagnostic rationale.
The key issues of cryptogenic pneumonia assessment revolve around exclusion of other disorders which would contraindicate high dose steroids used in the treatment of COP. Candidates who included this in their answer were able to demonstrate an expert level of understanding.


Neither cryptogenic organising pneumonia, nor any of the other nonresolving pneumonias and noninfectious mimics, has ever appeared in the exam previously, even though it is "a known clinical scenario with important diagnostic ramifications".

a) The possibilities are endless. If one had to be limited to merely five differentials, one would be forced to choose from among the following:

  • Atypical pneumonia (Legionella, Mycobacteria, Chlamydia, viruses, etc)
  • Fungal pneumonia (eg. Aspergillus)
  • Drug toxicity pneumonitis (eg. gemcitabine or methotrexate)
  • Eosinophilic pneumonia (eg. DRESS or Churg-Strauss)
  • Pulmonary sarcoidosis
  • Pulmonary vasculitis
  • Lymphangitis carcinomatosis
  • Idiopathic interstitial pneumonias (eg. NSIP)
  • Mucinous lung carcinoma

b) "Assessment" should be framed in terms of "history, examination, investigations".  Unfortunately examination for COP is usually pointless; or rather it involves excluding other differentials. Thus:

  • History suspicious of COP:
    • Subacute course
    • Constitutional symptoms (fevers, malaise, fatigue, etc)
    • Often follows confirmed infectious pneumonia
    • Fails to improve with antibiotics
    • Cough is usually not productive
  • Examination
    • mainly to exclude malignancy and systemic vasculitic processes
  • Investigations suspicious of COP: 
    • Bloods: inflammatory markers are only modestly raised
    • Cultures are negative
    • Autoimmune screen (ANA, ENA, RF, ANCA) is negative
    • Specific radiological findings on CT:
      • Peripheral consolidation with air bronchograms
      • Perilobular pattern, forming "arcades"
      • Bronchocentric distribution of consolidation
      • Band-like consolidation
      • "Reverse Halo" sign 

c) Rationale for BAL here was only weighed 25% of the marks. That would likely look like this:

  • COP is an inflammatory condition the management of which requires high dose steroids, and a long tapering course
  • COP is also a mimic of other, infectious causes of pneumonia
  • It is therefore essential to exclude infection before embarking on a course of high dose steroids
  • BAL will also potentially produce cell count values supportive of the diagnosis of COP. Specifically, lymphocytosis seems to be a common feature.
  • BAL can also exclude some of the non-infectious differentials, such as eosinophilic pneumonia and malignancy.


Cordier, Jean-François. "Organising pneumonia." Thorax 55.4 (2000): 318-328.

Baque-Juston, M., et al. "Organizing pneumonia: what is it? A conceptual approach and pictorial review." Diagnostic and interventional imaging 95.9 (2014): 771-777.

Tiralongo, Francesco, et al. "Cryptogenic organizing pneumonia: evolution of morphological patterns assessed by HRCT." Diagnostics 10.5 (2020): 262.

Roberton, Benjamin J., and David M. Hansell. "Organizing pneumonia: a kaleidoscope of concepts and morphologies." European radiology 21.11 (2011): 2244-2254.

Drakopanagiotakis, Fotios, et al. "Cryptogenic and secondary organizing pneumonia: clinical presentation, radiographic findings, treatment response, and prognosis." Chest 139.4 (2011): 893-900.