Asthma is a heterogeneous disease characterized by chronic inflammatory disease of the airways and notable for hyper-responsivity to multiple exacerbating stimuli. While a chronic condition, asthma is generally an intermittent disease with acute exacerbations interspersed with symptom-free periods. In severe cases, some patients may experience some symptoms of airway obstruction daily.

An estimated 26 million people in the United States have asthma (7 million children), and the condition is a leading cause of absence from school.

The course of asthma over time varies greatly in this age group. Children developing symptoms of asthma before age 3 years face the greatest deficits in lung function growth over time compared to those with asthma symptoms first presenting after age 3 years.

The condition has genetic as well as environmental determinants. Roughly one-half of cases are due to genetic susceptibility and one-half are related to environmental factors.

Immunohistopathologic features of asthma include inflammatory cell infiltration with neutrophils, eosinophils, lymphocytes, mast cell activation, and epithelial injury.

Exacerbations are manifested by widespread narrowing of airways that may resolve spontaneously or with therapy. This narrowing of airways results in the experience of dyspnea, cough, and wheezing. Triggers for such exacerbations include allergens, exercise, cold air, viral or bacterial infection, etc. These episodes last for minutes to hours and can be self-resolving or may be severe enough to cause respiratory failure and death in the absence of emergency and intensive care.

Although the symptoms of asthma (cough, dyspnea, wheezing) are generally nonspecific, several components of patient history may help point toward this diagnosis:

• Asthma symptoms typically are episodic and worsen at night.
• Common asthma triggers include environmental allergens (eg, dust mites, molds, furry animals, cockroaches, pollen), exercise (symptoms trigger approximately 5 minutes after brief exercise or 15 minutes into sustained exercise and resolve with rest), cold air, and viral infections.
• A family history of atopy (history of asthma, allergies, atopic dermatitis) favors asthma in a patient with compatible respiratory symptoms.

The clinical examination is most notable for widespread, high-pitched wheezing generally noted on expiration. Wheeze may not be present if the patient is asymptomatic and between exacerbations. It may also be absent in severe disease and limited air movement.

Other physical findings of severe obstruction include nasal flaring, subcostal retractions, use of accessory muscles such as the sternocleidomastoids, sitting in a tripod position, and a prolonged expiratory phase. Hypertension is frequently increased in patients with asthma.

Asthma is generally divided into 2 types: allergic asthma (caused by exposure to an allergen) and nonallergic asthma.

Asthma occurs at all ages but predominantly in early life. One-half of cases develop in the first decade of life, and another third present in the first 4 decades of life. Patients may experience remission of symptoms in puberty and recurrence in adulthood. The single largest risk factor for the development of asthma is atopy, and allergic asthma is associated with a familial or personal history of allergic diseases. These patients may have positive skin test reactions to intradermal antigen testing and/or elevated levels of immunoglobulin E (IgE). Nonallergic asthma patients do not have such histories of allergy and have negative skin testing and normal IgE levels.

Indoor gas stove use for cooking is associated with an increased risk of asthma among children.