From the Guidelines
Cryptogenic Organizing Pneumonia (COP) is distinguished from other forms of organizing pneumonia by its idiopathic nature and the absence of an identifiable cause, making it "cryptogenic" (of unknown origin) 1. The diagnosis of COP is made after thoroughly excluding all potential causes such as infections, drug reactions, connective tissue diseases, radiation exposure, or inhalation injuries. Key characteristics of COP include:
- A subacute illness of relatively short duration (median, less than 3 months) with variable degrees of cough and dyspnea 1
- Patchy and often migratory consolidation in a subpleural, peribronchial, or bandlike pattern on HRCT, commonly associated with ground-glass opacity 1
- Perilobular opacities and reversed halo (or atoll) sign may be helpful in suggesting the diagnosis 1
- Small unilateral or bilateral pleural effusion may occur in 10-30% of patients 1 Treatment of COP typically involves corticosteroids, with most patients responding well within days to weeks, and 65-80% achieving complete recovery 1. However, relapses can occur in 13-58% of cases, especially during steroid tapering, and may require the addition of immunosuppressants like cyclophosphamide, azathioprine, or mycophenolate mofetil for steroid-resistant cases. The distinction between COP and secondary organizing pneumonia is crucial, as treating any underlying cause is essential for secondary cases, while COP requires focus on immunosuppressive therapy alone 1.
From the Research
Characteristics of Cryptogenic Organizing Pneumonia (COP)
- COP is a distinct clinical and pathologic entity, characterized by dyspnea, cough, and multiple patchy alveolar opacities on pulmonary imaging 2, 3, 4
- The diagnosis of COP is established by combining clinical, radiological, and histological criteria, with the finding of buds of granulation tissue in the distal airspaces at lung biopsy being definitive 3, 4
- COP is considered to have a good prognosis and is generally responsive to corticosteroid treatment, although relapses are common 2, 5, 4
Comparison with Secondary Organizing Pneumonia (SOP)
- Secondary OP (SOP) occurs in association with identifiable medical conditions, such as infection, cancer, and radiation pneumonitis 5, 6
- The clinical presentation and radiographic findings of COP and SOP are similar and nonspecific, making it difficult to differentiate between the two conditions clinically 2, 6
- Some laboratory results, such as lymphocyte counts in bronchoalveolar lavage (BAL) fluid, may differ significantly between COP and SOP 6
- The presence of pleural effusion is more common in SOP than in COP 6
- The prognosis and treatment response of COP and SOP are similar, although recurrence rates may be higher in SOP patients treated with steroids 6
Distinctive Features of COP
- The absence of an identifiable cause, such as infection or associated disease, distinguishes COP from SOP 2, 4
- The rapid effectiveness of corticosteroid treatment in COP, although relapses are common, is a distinctive feature of the condition 5, 4
- The presence of buds of granulation tissue in the distal airspaces at lung biopsy is a characteristic histological feature of COP 3, 4