(acronym for Cryptogenic Organized Pneumonia)

Rare. Lung disease belonging to the idiopathic interstitial lung disease group, in which tissue granulation buds obstruct alveolar ducts and spaces, with chronic inflammation of adjacent alveoli. The clinical and radiological manifestations are similar to those of a pulmonary infection: it is therefore useful to evoke this diagnosis in the presence of persistent signs of respiratory infection despite antibiotic therapy.

Some experts describe a three-phase course:

1)        an early phase of alveolar epithelial involvement, with necrosis and desquamation of type I pneumocytes. This produces a fibrin deposit in the alveolar lumen, associated with an inflammatory infiltrate (lymphocytic, neutrophilic and eosinophilic).

2)        a phase of fibro-inflammatory bud formation. The fibrin is degraded by macrophages, and the inflammatory cells are progressively replaced by fibroblasts migrating from the pulmonary interstitium. They transform into myofibroblasts, and are embedded in a collagen-rich connective tissue matrix.

3)        a phase of maturation of the endoluminal buds, with almost complete disappearance of inflammatory cells and organization into concentric layers of myofibroblasts and connective tissue. At the same time, the alveolar epithelium proliferates, gradually restoring its architecture.

The main symptoms are a dry cough, exertional dyspnea and flu-like symptoms with fever. Functionally, a mild to moderate restrictive syndrome is observed in 30-55 % of cases, and a CO diffusion disorder in 40-75 % of cases. Hypoxemia at rest or during exercise is described in 30 to 85 % of cases.

Conventional chest radiography usually shows bilateral alveolar infiltrates in scattered patches, predominantly in the periphery. Another typical radiological feature is the migratory nature of the opacities, described in 10 to 40 % of cases. More rarely, a diffuse reticulo-nodular interstitial infiltrate, a mixed alveolar-interstitial appearance, or a solitary lesion with the appearance of a nodule or mass. Cavitary lesions or pleural effusion are rarely described. In over 80 % of cases, the thoracic CT scan shows multiple areas of bilateral alveolar consolidation, either subpleural or peribronchovascular.

POC lesions are characterized by an excellent response to corticosteroid therapy: prednisone 0.75 mg/kg/day for four weeks, then 0.5 mg/kg/day for four weeks, followed by a gradual reduction. Macrolide antibiotics are also highly effective.

The recurrence rate is not negligible, ranging from 10 to 60 %. Risk factors for recurrence are poorly understood, but seem to include cholestasis and marked hypoxemia at the time of diagnosis.

Anesthetic implications:

hypoxemia responding poorly to oxygen therapy

References:

-        Lebowitz D, Gex G, Pache J-C, Rochat T.
La pneumonie organisée cryptogénique.
Revue Médicale Suisse 2013; 407

-        King TE Jr, Lee JS.
Cryptogenic Organizing Pneumonia. 
N Engl J Med 2022;386:1058-69. doi:10.1056/NEJMra2116777

Updated: April 2024