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For further information, see CMDT Part 9-05: Asthma

Key Features

Essentials of Diagnosis

  • Episodic or chronic symptoms of wheezing, dyspnea, or cough

  • Symptoms frequently worse at night or in the early morning

  • Prolonged expiration and diffuse wheezes on physical examination

  • Limitation of airflow on pulmonary function testing or positive bronchoprovocation challenge

  • Reversibility of airflow obstruction, either spontaneously or following bronchodilator therapy

General Considerations

  • Characterized by variable airway obstruction, airway hyperresponsiveness, and airway inflammation

  • No single histopathologic feature is pathognomonic but common findings include

    • Airway inflammatory cell infiltration with eosinophils, neutrophils, and lymphocytes (especially T cells)

    • Goblet cell hyperplasia, sometimes plugging of small airways with mucus

    • Collagen deposition beneath the basement membrane

    • Hypertrophy of bronchial smooth muscle

    • Airway edema

    • Mast cell activation

    • Denudation of airway epithelium


  • Affects approximately 8–10% of the population

  • Each year, approximately 10 million office visits, 1.8 million emergency department visits, and more than 3500 deaths in the United States are attributed to asthma

Clinical Findings

Symptoms and Signs

  • Characterized by

    • Episodic wheezing

    • Shortness of breath

    • Chest tightness

    • Cough

  • Symptoms vary over time, vary in intensity, and are often worse at night or in the early morning

Differential Diagnosis

  • Upper airway disorders

    • Vocal fold paralysis, vocal fold dysfunction syndrome

    • Narrowing of the supraglottic airway

    • Laryngeal masses or dysfunction

  • Lower airway disorders

    • Foreign body aspiration

    • Tracheal masses or narrowing, tracheobronchomalacia

    • Airway edema (eg, angioedema or inhalation injury)

    • Nonasthmatic chronic obstructive pulmonary disease (COPD)

    • Bronchiectasis

    • Allergic bronchopulmonary mycosis

    • Sarcoidosis

    • Cystic fibrosis

    • Eosinophilic pneumonia

    • Hypersensitivity pneumonitis

    • Bronchiolitis obliterans

  • Systemic vasculitis with pulmonary involvement, such as eosinophilic granulomatosis with polyangitis

  • Cardiac disorders (heart failure, pulmonary hypertension)

  • Psychiatric causes include conversion disorders ("functional" asthma) and emotional laryngeal wheezing or episodic laryngeal dyskinesis


Laboratory Findings

  • Arterial blood gas measurements may be normal during a mild exacerbation

  • However, respiratory alkalosis and an increase in the alveolar-arterial oxygen difference (A–a–DO2) are common

  • During severe exacerbations, hypoxemia develops and the PaCO2 returns to normal

  • The combination of an increased PaCO2 and respiratory acidosis may indicate impending respiratory failure and the need for mechanical ventilation

Pulmonary function testing

  • Spirometry helps determine the presence and extent of airflow obstruction and whether it is immediately reversible

  • Bronchial provocation testing may be useful when asthma is suspected but spirometry is nondiagnostic

  • Peak expiratory flow (PEF) meters can

    • Establish peak flow variability

    • Quantify asthma severity

    • Provide both patient and clinician objective measurements on which to base treatment decisions


  • Chest radiographs

    • Usually normal or show only hyperinflation

    • Other findings may include ...

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