AAO-HNSF Primary Care Otolaryngology Handbook

CHAPTER 9

Allergy

Clinical Practice Guideline: Allergic Rhinitis

Millions of Americans suffer from inhalant allergies. Symptoms include sneezing; nasal congestion; runny nose; postnasal drainage; watery eyes; and itchy ears, eyes, nose, and palate. Sleep-disordered breathing is common among allergic patients and is often manifested as fatigue. Symptoms are triggered by environmental exposures and may be seasonal, year-round/perennial, or episodic in nature based on exposure to the offending allergen. If one parent has inhalant allergies, a child has a 30–50 percent chance of developing allergies; if both parents have allergies, this increases to about 60–80 percent. The percentage of the population with allergy problems has been increasing in developed countries. One possible explanation for this is that the infectious diseases more common in less developed coun- tries help tilt an individual’s immune system more toward the T-helper 1 (Th1) system, minimizing the chance of developing the Th2-mediated atopic reaction, and the resulting allergic symptoms. Allergies represent an abnormal immune response to the environment otherwise tolerated by the majority of people. Various antigens, or aller- gens, can trigger inhalant allergies, such as animal dander, pollens, mold spores , and dust mite. Typically, trees pollinate and cause symptoms in the spring, grasses pollinate in the summer, and weeds pollinate in the fall. Allergens, such as house dust mites , cockroaches , animal dander, and molds, can cause symptoms year-round. Initial contact of immunoglobulin M with an allergen generates immuno- globulin E (IgE)-specific antibodies to this allergen. Theses IgE antibodies bind to IgE receptors on mast cells in the tissues. Upon a second expo- sure to the allergen, a Gell–Coombs Type I hypersensitivity reaction is triggered and mediated by the allergen-specific IgE on the mast cells, resulting in degranulation and release of allergic mediators into the system. Allergic mediators responsible for the immediate response to an allergen include histamine—the most important—and various cytokines,

53

www.entnet.org