Rhinitis - Allergic Disease Background

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.