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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 on pulmonary function tests

  • Minimal findings on chest radiograph, heterogeneous airflow obstruction, air trapping

  • Relevant exposure or risk factors

    • 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

  • Bronchiolitis is more common in children than in adults and is usually caused by

    • Respiratory syncytial virus

    • Rhinovirus

    • Parainfluenza

    • Coronavirus

    • Adenovirus

  • Bronchiolitis is encountered in multiple clinical settings

    • Post-infectious

    • Inhalational injury (such as vaping)

    • Organ transplantation

    • Connective tissue diseases

    • Hypersensitivity pneumonitis

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

Classification and Histopathologic Findings

  • Constrictive bronchiolitis

    • Also referred to as obliterative bronchiolitis, or bronchiolitis obliterans

    • Most common finding following inhalation injury (ammonia, welding fumes, and heavy metals)

    • May also be seen in

      • Rheumatoid arthritis

      • Medication reactions (busulfan, gold, and penicillamine)

      • Chronic rejection following heart-lung, lung, or hematopoietic stem cell transplantation (bronchiolitis obliterans syndrome)

    • Characterized by

      • Patchy chronic inflammation

      • Concentric submucosal and peribronchiolar fibrosis

      • Smooth muscle hypertrophy causing luminal obstruction (obliteration)

  • Proliferative bronchiolitis

    • Also called "organizing pneumonia"

    • 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

  • 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

      • Sjögren syndrome

      • Immunodeficiency states (eg, HIV, common variable immunodeficiency)

  • 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


  • Diffuse panbronchiolitis

    • Most frequently diagnosed in Japan

    • Men are affected about twice as often as women

    • Only one-third are smokers

Clinical Findings

Symptoms and Signs

  • Constrictive bronchiolitis: progressive, deteriorating clinical course

  • Follicular bronchiolitis: may be seen in lymphoid interstitial pneumonia

  • Respiratory bronchiolitis

    • Most common form of bronchiolitis in adults

    • Usually related to cigarette smoking

    • Usually asymptomatic

    • Usually occurs without physiologic evidence of lung impairment

    • May be seen ...

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