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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 induced after exposure to allergens. It is also known as hay fever or allergic rhinosinusitis.
Epidemiology
It affects approximately 25% of children and 40% of adults worldwide. 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 may be various
diatheses for allergic rhinitis sensitization, but the most important
mechanisms are genetic factors and the production of IgE antibody.
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 pets.
There are two phase reactions in allergic rhinitis. The early phase reaction happens when histamine and leukotrienes are released from mast cells and irritate the sensory nerve endings and blood vessels of the nasal mucosa. This irritation causes sneezing, rhinorrhea (watery), 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 it causes 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 impaired daily
activities, leisure, and/or sports activities, impaired school or work
performance, sleep disturbance, or 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.