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For further information, see CMDT Part 9-10: Bronchiolitis
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Essentials of Diagnosis
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Insidious onset of cough and dyspnea
Irreversible airflow obstruction and air trapping on pulmonary function testing
Minimal findings on chest radiograph, heterogeneous airflow obstruction and air trapping on chest CT scan
Relevant exposure or risk factor
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General Considerations
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Bronchiolitis is a generic term applied to varied inflammatory processes that affect the bronchioles
Disorders associated with bronchiolitis include
Idiopathic cases are characterized by the insidious onset of dyspnea or cough
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Classification and histologic findings
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Acute bronchiolitis
Constrictive bronchiolitis
Also referred to as obliterative bronchiolitis, or bronchiolitis obliterans
Most common finding following inhalation injury
May also be seen in rheumatoid arthritis; drug reactions; and chronic rejection following heart-lung, lung, or bone marrow transplant
Characterized by
Patchy chronic inflammation
Concentric submucosal and peribronchiolar fibrosis
Smooth muscle hypertrophy causing luminal obstruction (obliteration)
Proliferative bronchiolitis
Occurs when there is an organizing intraluminal exudate, consisting of fibroblasts, lipid laden ("foamy") macrophages, and other cells that obstruct the bronchiolar lumen
These findings are more common than the constrictive pattern
Associated with diverse pulmonary disorders, including
Infection
Aspiration
Acute respiratory distress syndrome (ARDS)
Hypersensitivity pneumonitis
Connective tissue diseases
Organ transplantation
Cryptogenic organizing pneumonitis (COP)
Previously referred to as bronchiolitis obliterans with organizing pneumonia (BOOP)
A proliferative pattern that occurs when the organizing intraluminal exudate extends through the bronchiole into the alveolar space, with prominent intraluminal buds of fibroblasts embedded in immature collagen (see Table 9–17)
Follicular bronchiolitis
Characterized by chronic peribronchiolar inflammation and hyperplastic lymphoid follicles with reactive germinal centers arising from bronchus-associated lymphoid tissue (BALT)
Most commonly associated with connective tissue disease, especially rheumatoid arthritis and Sjögren syndrome, and with immunodeficiency states
Respiratory bronchiolitis
Affects small airways in cigarette smokers
Characterized by accumulation of pigmented alveolar macrophages within respiratory bronchioles, associated with mild interstitial fibrosis and chronic inflammation
In some patients, however, respiratory bronchiolitis causes diffuse parenchymal infiltrates
This syndrome is referred to as respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
It is considered to represent part of the spectrum of the smoking-related interstitial lung diseases
Diffuse panbronchiolitis
An idiopathic disorder of respiratory bronchioles
Characterized by a peribronchiolar mixed inflammatory cell infiltrate and accumulation of lipid laden ("foamy") macrophages within the interstitium and alveolar spaces
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