Allergic Rhinitis (Perennial and Seasonal)
Definition
An unusual sensitivity of the nasal lining to a substance (allergen), which results in the release of chemicals which cause sneezing, dilatation of the blood vessels of the mucous membranes and clear nasal discharge.
Incidence/Age
Affects 10% - 20% of the population and may develop at any age.
Causes
The agents which provoke a nasal allergic reaction (nasal allergens) are many and varied. Amongst the commonest are the faeces of the house dust mite, various pollen particles and particulate matter from animal fur eg: the proteins in dried cat saliva. They are usually airborne and easily inhale and may also evoke a similar reaction in the membranes of the eyelids and eyeball. Allergens which only appear in the environment at certain times of the year eg: pollens and mould spores are said to cause a 'seasonal allergic rhinitis'. Allergens which are present in the environment all year round eg: dust mite faeces are said to cause 'perennial allergic rhinitis'.
Symptoms/Signs
After exposure to an allergen the eyes may become red, itchy and water. The nose itches causing sneezing and the mucus gland secrete copious clear fluid making the nose run. The blood vessels of the mucous membranes dilate causing swelling and nasal blockage. The roof of the mouth may also itch, the throat may feel sore and associated wheezing may occur in up to 50% of sufferers. The symptoms may be seasonal, dependent upon the season in which the allergen exposure rate is highest (eg, high pollen count in the summer months).
Examination of the nasal mucous membranes will show them to be pale, boggy and swollen. In children repeated rubbing of an itchy nose may result in the development of a horizontal crease in the skin just above the bulbous nasal tip ' the nose rubbers crease'.
Complications of Disorder
In children in particular allergic rhinitis may be complicated by middle ear infection (acute otitis media) glue ear and sinus infection. Occasionally a severe asthma attack may be precipitated.
Tests
The diagnosis of allergic rhinitis is usually obvious from the history, but further tests may be useful if the diagnosis is in doubt. Skin prick testing is used to test for sensitivity to specific allergens. Tiny superficial scratches are made in the skin, usually on the forearm, and a solution containing the allergen to be tested is then placed over each scratch. If the patient is sensitive to the allergen, after a few minutes a pink bump will appear around the scratch. This is the result of the release of a chemical called histamine from the reactive cells (mast cells) in the skin. Some drugs may abolish this reaction so the patient should always be asked about their current medication or the result of the test may not be valid. This drug effect may be very long lasting (up to 28 days with some antihistamine drugs).
Some patients have sensitive skin and will swell to such a degree after the skin prick with no allergen that the test is not interpretable. Specific blood tests (RAST Tests) can be used in such cases to detect the signs of immune reactions to specific allergens.
Treatment
Allergen avoidance - The most effective methods of allergen avoidance usually involve avoiding places where there is a high allergen load eg: fields of flowering oil seed rape or ragweed. Attempts to reduce the amount of allergen in ones usual environment are often less successful. House dust mites are usually present in bedding and mattresses and close weave barrier sheets and duvet covers may reduce the number reaching the sufferers face. Similarly removing soft furnishings, soft toys and carpets may reduce dust and mite levels. Dusting with a damp duster reduces the amount of airborne dust and thus the amount inhaled.
Source: www.privatehealth.co.uk
Last Editorial Review: 25/1/2010
