DEFINITION OF ALLERGIC RHINITIS
Rhinitis is characterized by sneezing; rhinorrhea; obstruction of the nasal passages; conjunctival, nasal, and pharyngeal itching; and lacrimation and can be classified as allergic or non-allergic. A clinical history of rhinitis symptoms occurring in a temporal relationship to allergen exposure and documentation of sensitization to an environmental allergen are required for a diagnosis of allergic rhinitis. Although commonly seasonal due to elicitation by airborne pollens, it can be perennial in an environment of chronic exposure to house dust mites, animal danders, or insect (cockroach) products. The overall prevalence in North America has increased in the past 20 years and is 10–30%, with the peak prevalence of >30% occurring in the fifth decade.
PREDISPOSING FACTORS AND ETIOLOGY OF ALLERGIC RHINITIS
Allergic rhinitis generally occurs in atopic individuals, often in association with atopic dermatitis, food allergy, urticaria, and/or asthma (Chap. 281). Up to 50% of patients with allergic rhinitis manifest asthma, whereas 70–80% of individuals with asthma and 80% of individuals with chronic bilateral sinusitis experience allergic rhinitis. Female sex, particulate air pollution exposure, and maternal tobacco smoking increase the risk of developing allergic rhinitis over the life span.
Trees, grasses, and weeds that depend on wind rather than insects for pollination produce sufficient quantities of pollen suitable for wide distribution by air currents to elicit seasonal allergic rhinitis. The dates of pollination of these species historically varied little from year to year in a particular locale, but may be quite different in another climate. In the temperate areas of North America, trees typically pollinate from March through May, grasses in June and early July, and ragweed from mid-August to early October. Molds, which are widespread in nature because they occur in soil or decaying organic matter, propagate spores in a pattern that depends on climatic conditions. Climate change is impacting these patterns with early tree pollination and prolonged ragweed season with the delay of the first frost. Perennial allergic rhinitis occurs in response to allergens that are present throughout the year, including animal dander, cockroach-derived proteins, mold spores, or dust mites such as Dermatophagoides farinae and Dermatophagoides pteronyssinus. Dust mites are scavengers of human skin and excrete cysteine protease allergens in their feces. In up to 40% of patients with perennial rhinitis, no clear-cut allergen can be demonstrated as causative.
PATHOPHYSIOLOGY AND MANIFESTATIONS OF ALLERGIC RHINITIS
Episodic rhinorrhea, sneezing, obstruction of the nasal passages with lacrimation, and pruritus of the conjunctiva, nasal mucosa, and oropharynx are the hallmarks of allergic rhinitis. The nasal mucosa is pale and boggy, the conjunctiva congested and edematous, and the pharynx generally unremarkable. Swelling of the turbinates and mucous membranes with obstruction of the sinus ostia and eustachian tubes precipitates secondary infections of the sinuses and middle ear, respectively. A growing number of patients with seasonal allergic rhinitis demonstrate pollen-associated food allergen syndrome characterized ...