Cryptogenic organising pneumonia is characterised by all of the following except –
**Core Concept**
Cryptogenic organizing pneumonia (COP) is a type of lung disease characterized by the presence of organizing pneumonia, which is a specific histopathological pattern. It is a form of diffuse lung disease that is not caused by an identifiable etiology.
**Why the Correct Answer is Right**
COP is typically characterized by the following features: bilateral infiltrates on chest radiography, a pattern of organizing pneumonia on lung biopsy, and a response to corticosteroid treatment. The histopathological hallmark of COP is the presence of buds of granulation tissue within the alveoli, which is a result of the abnormal repair of damaged lung tissue. This process is mediated by the proliferation of fibroblasts and the deposition of extracellular matrix.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because COP is indeed characterized by a progressive decline in lung function, as evidenced by a decrease in forced vital capacity (FVC) and forced expiratory volume in one second (FEV1).
**Option B:** This option is incorrect because COP is typically associated with a normal or elevated level of eosinophils in the peripheral blood, which is in contrast to other forms of lung disease such as eosinophilic pneumonia.
**Option C:** This option is incorrect because COP is not typically associated with a high level of autoantibodies, such as anti-neutrophil cytoplasmic antibodies (ANCA) or anti-synthetase antibodies.
**Clinical Pearl / High-Yield Fact**
A key feature of COP is its responsiveness to corticosteroid treatment, with many patients experiencing significant improvement in symptoms and lung function within a few weeks of starting treatment.
**Correct Answer:** D