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Allergic rhinitis is a chronic inflammatory disease of the upper airways caused by immunoglobulin E (IgE) sensitization to airborne allergens in genetically susceptible individuals. The clinical presentation is characteristically associated with frequent sneezing, nasal congestion, and nasal discharge. As many as 60% of patients with allergic rhinitis complain or display ocular symptoms (ie, itchy/watery eyes); thus it is termed allergic rhinoconjunctivitis (ARC), the term by which it is better known. Allergic rhinitis is subdivided into seasonal and perennial types based on time of occurrence and duration of symptoms. Allergic rhinitis can affect a child’s quality of life and can be associated with conditions such as sleep disturbances and learning difficulties. This chapter will provide an overview of the epidemiology, pathogenesis, diagnosis, and management of allergic rhinoconjunctivitis.
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There is a wide variation in the prevalence of ARC worldwide. In the United States, symptoms of ARC can occur in 10% to 30% of adults and as many as 40% of children. In the pediatric group, the numbers range from 0.8% to 14.9% in 6- to 7-year-olds and from 1.4% to 39.7% in 13- to 14-year-olds. The reasons behind these disparities are not completely understood, but both environmental and genetic factors are likely to play a role. Like other allergic diseases, the prevalence of ARC seems to be on the rise, particularly in industrialized countries. Risk factors for developing allergic rhinitis include family history of atopy, higher socioeconomic class, having a serum IgE > 100 IU/mL before 6 years of age, and evidence of sensitization.
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Aeroallergen sensitization can occur between 6 months and 2 years of life, especially in children with a family history of atopy; however, it is uncommon for sensitization to occur before 6 months of age. The classical symptoms of seasonal allergic rhinitis do not typically develop until the child reaches 2 to 7 years of age. In childhood, allergic rhinitis occurs more frequently in boys, but in adults, occurs more frequently in women. The prevalence of seasonal allergic rhinitis is higher in children and adolescents, whereas perennial allergic rhinitis has a higher prevalence in adults.
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The pathogenesis of ARC responds to the same immune mechanisms as do other allergic disorders. In this case, exposure to airborne allergens, in a genetically susceptible individual, initiates the series of events that lead to the local activation of allergen-specific T cells with a Th2 bias that directs the production of inflammatory cytokines, chemokines, and allergen-specific IgE. Upon reexposure to the same allergen, allergen-specific IgE bound to the Fcε receptors on mast cells cross-link and trigger the release of preformed mediators. Histamine released by mast cells is largely responsible for the immediate symptoms associated with ARC such as sneezing, itching, and rhinorrhea. Late responses are characterized by the recruitment of inflammatory cells to the nasal mucosa. These cells, which include eosinophils, basophils, lymphocyte, monocytes, and ...