Allergic rhinitis update: Epidemiology and natural history

Allergic rhinitis is the most common chronic condition, with an estimated p revalence in the United States of 5-22%, which increases from infancy, peak s in childhood and adolescence, and decreases in the elderly. As a major ca use of morbidity, absenteeism, and restricted activity in both children and adults, allergic rhinitis, similar to asthma, appears to be increasing wit h time. Allergic rhinitis is commonly defined as seasonal or perennial, dep ending upon whether symptoms are manifested at defined yearly intervals or throughout the year, respectively. While trees, grasses, weeds, and molds a re the most frequent causes of seasonal allergic rhinitis, dust mites and m olds are the major contributors to perennial allergic rhinitis. The pathoge nesis of allergic rhinitis is based upon inter-actions of allergen with mem brane-bound allergen-specific IgE on the surface of mediator cells, i.e., b asophils and mast cells, leading to the release of allergic mediators (both preformed and newly synthesized) including histamine, leukotrienes, and eo sinophil cationic protein (ECP). These are responsible for both immediate a llergic responses characteristic of acute allergic rhinitis and the late in flammatory reactions responsible for chronic allergic rhinitis. The evaluat ion of rhinitis should include a derailed patient history, a careful physic al examination, and appropriate diagnostic tests including skin prick tests or serum assays for allergen-specific IgE. Seasonal allergic rhinitis is r eadily distinguished from perennial allergic rhinitis by history and confir med by positive skin tests to causative aeroallergens. It is important to d ifferentiate seasonal rhinitis from non-allergic disorders including infect ious rhinitis, structural or anatomic problems such as nasal polyps ol sept al deviation, rhinitis medicamentosa (due to the overuse of topical vasocon strictors), hormonal rhinopathy (e.g., pregnancy, hypothyroidism), non-alle rgic vasomotor rhinopathy, non-allergic inflammatory rhinitis with eosinoph ils (NARES), or rarely, a neoplasm. A knowledge of the epidemiologic and cl inical presentation of allergic rhinitis together with these pathophysiolog ic mechanisms is essential for a modem-day diagnostic and therapeutic appro ach do the patient who suffers from allergic rhinitis.