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

Demographics

• 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

Diagnosis

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

Imaging

• Chest radiographs

  • Usually normal or show only hyperinflation

  • Other findings may include bronchial wall thickening and diminished peripheral lung vascular shadows