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