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Cryptogenic organising pneumonia

Dr Charlie Chia-Tsong Hsu and Dr Ekta Dhamija et al.

Cryptogenic organising pneumonia (COP) is a disease of unknown aetiology. A variety of infectious as well as non infectious causes have been associated.

Organizing pneumonia (OP) is a histologic pattern of alveolar inflammation with varied aetiology (including pulmonary infection). The idiopathic form of OP is called cryptogenic organizing pneumonia (COP) and it belongs to idiopathic interstitial pneumonias (IIP's).

COP was previously termed bronchiolitis obliterans organizing pneumonia (BOOP) : (not to be confused with bronchiolitis obliterans per se).8

Epidemiology and clinical presentation

Presentation is commonest in the 55 - 60 age group. Patients present with short history (i.e less than ~ 2 months) of breathlessness, non productive cough, weight loss, malaise and fever.  There is no association with smoking.

Pathology

In addtion to the alveolar inflammatory changes found with a normal pneumonia, there is also involvement of the bronchioles.

Histologically, it is characterized by the presence of buds of granulation tissue (Masson bodies) in the distal airspaces which may cause secondary bronchiolar occlusion due to extension of the inflammatory process. Hence, the reason for being perviously termed bronchiolitis obliterans organizing pneumonia (BOOP).

Radiographic features

Chest radiograph
  • consolidation
    • bilateral patchy areas ( commonest finding 3 ) : often migratory
    • can affect all lung zones
    • usually peripheral, sub-pleural, peribronchovascular 2
  • nodules
    • foci of granulation tissue up to 1 cm
    • may simulate neoplasm if > 5 cm in size
    • may be numerous in immunocompromised patients
HRCT

The most common HRCT features include 6:

  • patchy consolidation with a predominantly subpleural and / or peribronchial distribution
  • small, ill-defined peribronchial or peribronchiolar nodules
  • large nodules or masses
  • bronchial wall thickening or dilatation in the abnormal lung regions
  • a perilobular pattern with ill-defined linear opacities that are thicker than the thickened interlobular septa and have an arcade or polygonal appearance
  • ground glass opacity or crazy paving

The reverse halo sign (atoll sign) is considered to be highly specific ,although only seen in ~ 20% of patients with COP 5 

Etymology

It was first described by Davison and colleagues in 1983.

Treatment and prognosis

Corticosteroids have been widely used and most patients recover completely 3-4. 

Differential diagnosis

On plain film consider
On HRCT consider
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