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Introduction
Allergic rhinitis is a symptomatic disorder of the nose secondary to immunoglobulin E (IgE)-mediated inflammation of the nasal membranes resulting from exposure to allergens of a sensitized individual. It is also known as hay fever or allergic rhinosinusitis.
Epidemiology
The prevalence of allergic rhinitis ranges from approximately 5-10% worldwide, with the highest incidence in the pediatric population but less prevalent in children under 2 years old. Its estimated prevalence in Europe and the United States is 30%. Approximately 80% of symptoms of allergic rhinitis develop before 20 years of age.
Pathophysiology
There are various
diatheses for allergic rhinitis sensitization, but the most important
mechanisms are interactions between genetic, environmental,
lifestyle, and socioeconomic factors.
Most allergic rhinitis is caused by inhalation of antigens
such as dermatophagoides (antigen in house dust) and pollens (eg trees, grasses,
and weeds) which are the most common. Other causes include fungi and pet dander.
Rhinitis - Allergic (Disease Background)The immunologic basis of allergic reactions occurs in 2 phases. The early phase reaction happens involves the sensitization and development of memory T and B cell responses, and IgE. Histamine and leukotrienes are then released from mast cells and irritate the sensory nerve endings and blood vessels of the nasal mucosa. This irritation causes sneezing, watery rhinorrhea, nasal mucosal swelling, or blockage. The late phase reaction happens when inflammatory cells like activated eosinophils infiltrate the nasal mucosa that is exposed to these antigens. The late phase reaction is usually seen 6-10 hours after exposure to antigens and results in mucosal swelling.
Classification
Classification According to
Severity of Symptoms
Mild allergic rhinitis symptoms do not interfere with
the quality of life as manifested by normal sleep, ability to perform normal
daily activities, sports, and leisure, normal performance at work or in school,
and without troublesome symptoms.
Moderate-severe allergic rhinitis symptoms interfere with the quality of life as manifested by one or more of the following: Impaired daily activities, leisure, and/or sport activities, impaired school or work performance, sleep disturbance, and troublesome symptoms.
Classification According to Frequency or Duration of
Symptoms
Intermittent allergic rhinitis is when symptoms
occur for <4 days/week or <4 consecutive weeks/year. Persistent allergic
rhinitis is when symptoms occur for ≥4 days/week and ≥4 consecutive weeks/year.
Patterns of Exposure to
Allergens
Seasonal allergic rhinitis is dependent on a
specific season. Perennial allergic rhinitis is a year-round allergen exposure and
usually presents in an everyday environment. Episodic allergic rhinitis is when
the patient is exposed to allergens not normally encountered in daily
activities. Occupational allergic rhinitis is when the condition is triggered
by allergens, chemicals, or irritants in the workplace and symptoms improve
when away from the workplace.