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For further information, see CMDT Part 9-10: Bronchiolitis

Key Features

Essentials of Diagnosis

  • 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

    • Toxic fumes

    • Viral infections

    • Organ transplantation

    • Connective tissue disease

General Considerations

  • Bronchiolitis is a generic term applied to varied inflammatory processes that affect the bronchioles

  • Disorders associated with bronchiolitis include

    • Organ transplantation

    • Connective tissue diseases

    • Hypersensitivity pneumonitis

  • Idiopathic cases are characterized by the insidious onset of dyspnea or cough

Classification and histologic findings

  • Acute bronchiolitis

    • Seen most commonly following viral infection in children

    • Has a neutrophilic and mononuclear infiltration in the absence of fibroblast proliferation or collagen deposition

  • 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

Table 9–17.Idiopathic interstitial pneumonias.

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