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 (PFT) or positive bronchoprovocation challenge.
Reversibility of airflow obstruction, either spontaneously or following bronchodilator therapy.
Asthma is a common disease, affecting approximately 8–10% of the population. It is slightly more common in male children (younger than 14 years) and in female adults. There is a genetic predisposition to asthma. Prevalence, hospitalizations, and fatal asthma have all increased in the United States over the past 20 years. 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. Hospitalization rates are highest among Black persons and children, and death rates are consistently highest among Black persons aged 15–24 years. The 2020 Global Initiative for Asthma (GINA) Report entitled Global Strategy for Asthma Management and Prevention is a comprehensive and practical resource that addresses asthma diagnosis, assessment, management, and exacerbations.
DEFINITION & PATHOGENESIS
Asthma is a chronic disorder of the airways 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; plugging of small airways with mucus; collagen deposition beneath the basement membrane; bronchial smooth muscle hypertrophy; airway edema; mast cell activation; and 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, respectively, of classic Th2 cytokines such as interleukin [IL]-4, IL-5, and IL-13) has been shown to be important regarding the selection of therapies.
Many clinical phenotypes of asthma have been identified. The most common is allergic asthma, which usually begins in childhood and is associated with other allergic diseases such as eczema, allergic rhinitis, or food allergy. Exposure of sensitive patients to inhaled allergens may cause symptoms immediately (immediate asthmatic response) or 4–6 hours after allergen exposure (late asthmatic response). Common allergens include house dust mites (often found in pillows, mattresses, upholstered furniture, carpets, and drapes), cockroaches, cat dander, and seasonal pollens. Substantially reducing exposure reduces pathologic findings and clinical symptoms. Allergic asthma falls into the T2-high endotype, as do late-onset T2-high asthma and aspirin/NSAID-associated respiratory disease. 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. Asthma with persistent airflow limitation is thought to be due to airway remodeling. Asthma with obesity refers to prominent respiratory symptoms in obese patients with little airway inflammation.
Nonspecific precipitants of asthma include upper respiratory tract infections, rhinosinusitis, postnasal drip, aspiration, gastroesophageal ...