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Key Features

Essentials of Diagnosis

  • Insidious onset of cough and dyspnea

  • Irreversible airflow obstruction on pulmonary function testing

  • Minimal findings on chest radiograph

  • 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 bronchiole into the alveolar space, with prominent intraluminal buds of fibroblasts embedded in immature collagen (see Table 9–18)

  • 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 9–18.Frequency of specific symptoms and signs in patients at risk for pulmonary thromboembolism.

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