Asthma

KEY FEATURES

Essentials of Diagnosis

• Respiratory symptoms such as wheezing, dyspnea, or cough, which may be variable in time and severity

• Variable limitation on expiratory airflow in pulmonary function testing (PFT) or positive bronchoprovocation challenge

General Considerations

• A chronic disorder of the airways characterized by variable airway expiratory obstruction and hyperresponsiveness

• Most common pathogeneses

  • Airway inflammation with eosinophils, neutrophils, and lymphocytes (especially T cells)

  • Goblet cell hyperplasia

  • Plugging of small airways with mucus

  • Collagen deposition beneath the basement membrane

  • Bronchial smooth muscle hypertrophy

  • Airway edema

  • Mast cell activation

  • Denudation of airway epithelium

• The pathophysiology of asthma is heterogeneous, but a division into T2-high and T2-low endotypes (marked by high and low levels of classic Th2 cytokines, including IL-4, IL-5, and IL-13) has been shown to be important in the selection of targeted biologic therapies

  • T2-high asthma phenotypes include allergic asthma, late-onset T2-high asthma, and aspirin/NSAID-associated respiratory disease (AERD)

  • T2-low asthma phenotypes include nonallergic asthma, which tends to occur in adults and be marked by neutrophilic inflammation and variable response to standard therapies

• Common aeroallergens

  • Dust mites

  • Cockroaches

  • Cat dander

  • Seasonal pollens

• Nonspecific precipitants

  • Respiratory tract infections, especially viral

  • Rhinosinusitis

  • Postnasal drip

  • Aspiration

  • Gastroesophageal reflux

  • Changes in weather

  • Stress

  • Exercise

• Asthma with persistent airflow limitation thought to be due to airway remodeling

• Asthma with obesity refers to prominent respiratory symptoms in patients with obesity with little airway inflammation

• Tobacco increases symptoms and decreases lung function

• Certain medications (including aspirin and nonsteroidal anti-inflammatory drugs [NSAID]) may be triggers (Table 9–22)

Demographics

• Affects 8–10% of the population in the United States

• Accounts for 10 million office visits, 1.8 million emergency department visits, and more than 3500 deaths annually in the United States

• Slightly more common in male children (< 14 years old) and in female adults

• There is a genetic predisposition to asthma

• Hospitalization rates have been highest among Black persons and children

• Death rates for asthma are consistently highest among Black persons aged 15–24 years