What are the key features of Cryptogenic Organizing Pneumonia (COP)?

From the Guidelines

Organizing pneumonia is a distinct form of pneumonia characterized by the presence of granulation tissue plugs within alveolar ducts and small airways, with key features including a clinical presentation of persistent cough, dyspnea, and flu-like symptoms, and radiological findings of bilateral patchy alveolar opacities with a peripheral distribution on chest imaging. The clinical presentation of organizing pneumonia typically includes persistent cough, dyspnea, and flu-like symptoms that fail to respond to antibiotics, as noted in the 2020 British Thoracic Society guideline 1. Radiologically, it typically shows bilateral patchy alveolar opacities with a peripheral distribution on chest imaging, often with ground-glass opacities and consolidation, as described in the 2013 American Thoracic Society/European Respiratory Society statement 1. Histologically, organizing pneumonia demonstrates polypoid plugs of granulation tissue (Masson bodies) within alveolar spaces and small airways, with preservation of the underlying lung architecture, as mentioned in the 2020 British Thoracic Society guideline 1. Some important features of organizing pneumonia include:

• Clinical presentation of persistent cough, dyspnea, and flu-like symptoms
• Radiological findings of bilateral patchy alveolar opacities with a peripheral distribution on chest imaging
• Histological demonstration of polypoid plugs of granulation tissue (Masson bodies) within alveolar spaces and small airways
• Preservation of the underlying lung architecture
• Potential for occurrence as a primary condition (cryptogenic organizing pneumonia) or secondary to various causes including infections, drugs, connective tissue diseases, and radiation therapy, as noted in the 2013 American Thoracic Society/European Respiratory Society statement 1. Treatment primarily involves corticosteroids, typically prednisone at 0.5-1 mg/kg/day for 1-3 months, followed by a slow taper over 6-12 months, as described in the example answer. Most patients respond well to steroids within days to weeks, with complete resolution in 65-80% of cases, though relapses can occur in about 13-58% of patients, particularly during steroid tapering, as mentioned in the example answer. In steroid-resistant cases, immunosuppressants like cyclophosphamide, azathioprine, or mycophenolate mofetil may be considered, as noted in the example answer. The prognosis is generally favorable, especially when diagnosed and treated promptly, as mentioned in the 2020 British Thoracic Society guideline 1.

From the Research

Important Features of Organizing Pneumonia

• Organizing pneumonia is a clinical entity associated with nonspecific symptoms and radiological findings, and abnormalities in pulmonary function tests 2.
• It is defined by the characteristic histopathological pattern of filling of alveoli and respiratory bronchioles by plugs of granulation tissue 2, 3.
• Organizing pneumonia can be idiopathic (COP) or secondary to other causes (SOP) 2, 3.
• The clinical presentation of OP often mimics that of other disorders, such as infection and cancer, which can result in a delay in diagnosis and inappropriate management of the underlying disease 3.
• The radiographic presentation of OP is polymorphous but often has subpleural consolidations with air bronchograms or solitary or multiple nodules, which can wax and wane 3.

Clinical Characteristics

• Dyspnea, cough, and fever are the most frequent symptoms of organizing pneumonia 2.
• Most patients have more than one tomographic pattern, with ground glass opacities and alveolar consolidation being the most common 2.
• The median age of patients with organizing pneumonia is 76 years, and the median time to diagnosis from the onset of symptoms is 31 days 2.
• The most frequent underlying cause of SOP is drug toxicity 2.

Diagnosis and Treatment

• Diagnosis of OP sometimes requires histopathologic confirmation and exclusion of other possible causes 3.
• Treatment usually requires a prolonged steroid course, and disease relapse is common 3, 4, 5.
• Adjunctive drugs, such as cyclosporine and macrolide, have been used in refractory cases with various outcomes 6.
• Second-line treatment options, including cyclophosphamide, azathioprine, and cyclosporin, have been used in combination with corticosteroids for corticosteroid-refractory forms of OP 4.