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For further information, see CMDT Part 9-05: Asthma
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Essentials of Diagnosis
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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
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General Considerations
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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
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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
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Differential Diagnosis
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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
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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
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Pulmonary function testing
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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
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