Cryptogenic organizing pneumonia
CRYPTOGENIC ORGANIZING PNEUMONIA (COP)
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) DEFINITION
Organising pneumonia is defined histopathologically by intra-alveolar buds of granulation tissue, consisting of intermixed myofibroblasts and connective tissue. Although nonspecific, this histopathological pattern, together with characteristic clinical and imaging features, defines cryptogenic organising pneumonia when no cause or peculiar underlying context is found. Rapid clinical and imaging improvement is obtained with corticosteroid treatment, but relapses are common after stopping treatment.
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) CAUSES
Organising pneumonia (OP) is a histologic pattern of alveolar inflammation with varied aetiology (including pulmonary infection). The idiopathic form of OP is called cryptogenic organising pneumonia (COP) and it belongs to idiopathic interstitial pneumonias (IIP’s).
COP was previously termed bronchiolitis obliteransorganising pneumonia (BOOP), not to be confused with bronchiolitis obliterans per se.
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) PATHOPHYSIOLOGY
The most intriguing characteristic of intra-alveolar fibrosis, resulting from organisation of inflammatory exudates, is its usual dramatic reversibility with corticosteroids. Although the intra-alveolar buds in organising pneumonia share some morphological features with the fibroblastic foci present in usual interstitial pneumonia (UIP), in contrast to the latter they are not associated with progressive irreversible fibrosis. Therefore, intra-alveolar fibrosis of organising pneumonia represents a unique model of inflammatory lung disease offering many similarities with the process of cutaneous wound healing.
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) SYMPTOMS
Clinical manifestations begin with a mild flu-like illness with fever, cough, malaise and progressively mild dyspnoea, anorexia and weight loss. Dyspnoea may occasionally be severe, especially in the eventuality of rapidly progressive disease. Haemoptysis is uncommon and seldom severe. Other uncommon manifestations include chest pain, night sweats and mild arthralgia (when arthralgia is prominent and/or associated with myalgia an underlying connective tissue disease should be suspected). Air leak (pneumothorax, pneumomediastinum) may be a rare presenting feature. Since the most common manifestations are nonspecific, diagnosis is often delayed (6–13 weeks). Physical examination usually discloses focal sparse crackles, but may be almost normal. There is no finger clubbing.
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) DIAGNOSIS
- High-resolution CT (HRCT)
- Sometimes surgical lung biopsy
Diagnosis requires imaging tests and, if the diagnosis is not otherwise clear, surgical lung biopsy. Chest x-ray shows bilateral, diffuse, peripherally distributed alveolar opacities with normal lung volumes; a peripheral distribution similar to chronic eosinophilic pneumonia may occur (see Chronic Eosinophilic Pneumonia). Rarely, alveolar opacities are unilateral. Recurrent and migratory pulmonary opacities are common. Rarely, irregular linear or nodular interstitial opacities or honeycombing are visible at presentation. HRCT of the lung shows patchy airspace consolidation (present in 90% of patients), ground-glass opacities, small nodular opacities, and bronchial wall thickening and dilatation. The patchy opacities are more common in the periphery of the lung, often in the lower lung zone. HRCT may show much more extensive disease than is expected from review of the chest x-ray.
Pulmonary function tests usually show a restrictive defect, although an obstructive defect (ratio of forced expiratory volume in 1 sec to forced vital capacity [FEV 1 /FVC] < 70%) is found in 21% of patients, and pulmonary function is occasionally normal.
Routine laboratory test results are nonspecific. Leukocytosis without an increase in eosinophils occurs in about one half of patients. The initial ESR often is elevated.
Lung biopsy shows excessive proliferation of granulation tissue within small airways and alveolar ducts, with chronic inflammation in the surrounding alveoli. Foci of organizing pneumonia are nonspecific and can occur secondary to other pathologic processes, including infections, vasculitis, lymphoma, and other interstitial lung diseases such as idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, connective tissue-related interstitial lung disease, drug induced pulmonary disease, hypersensitivity pneumonitis, and eosinophilic pneumonia.
CRYPTOGENIC ORGANIZING PNEUMONIA (COP) TREATMENT
Clinical recovery follows treatment with corticosteroids in most patients, often within 2 wk. COP recurs occur in up to 50% of patients. Recurrences appear related to the duration of treatment, so treatment should usually be given for 6 to 12 mo. Recurrent disease is generally responsive to additional courses of corticosteroids. Recovery after treatment is common when COP appears on HRCT as parenchymal consolidation, ground-glass opacity, or nodules. In contrast, recovery is less common when COP appears on HRCT as linear and reticular opacities.