What is Allergic Rhinitis?
Rhinitis means inflammation of the nasal lining or mucosa. It is characterized by chronic or recurrent sneezing, rhinorrhea (runny nose), itchy and blocked nose, which may be labeled as allergic when an allergen is identified. The most well known form of rhinitis is the common cold, which is infectious rhinitis due to a virus.
The hallmark of allergic rhinitis is the temporal relationship of symptoms on exposure to an allergen. Your nose, is not the only organ that may be affected in allergic rhinitis. You may have itching of your eyes (allergic conjunctivitis), throat and ears.
There are two types of allergic rhinitis:
Seasonal allergic rhinitis or Hay Fever
When symptoms are experienced only during spring and/or summer. It is usually due to various types of pollen, which are carried by the wind and easily breathed into the nose. When most people talk about hay fever it usually means seasonal allergic rhinitis.
Perennial allergic rhinitis
When symptoms are experienced all year round. It is usually caused by allergens such as house dust mite, particles from the family pets known as animal dander, or mould spores which are carried in the air.
Other causes of perennial rhinitis
Vets working with furred animals, bakers allergic to flour, health workers allergic to latex, etc.
Oral contraceptives, Hormone replacement therapy, aspirin & other non-steroidal anti-inflammatory drugs and antihypertensives can all cause rhinitis.
How common is allergic rhinitis?
Allergic rhinitis is estimated to have a prevalence of up to 40% in the New Zealand and Australian populations.
From a recent ISAAC Study* (using a standardized epidemiological method to survey the prevalence of allergic rhinitis in over 460,000 children aged 13-14 years from 155 centres in 56 countries worldwide) the prevalence varies from 1.4% to 39.7% worldwide. The lowest prevalences are found in parts of Eastern Europe, south and central Asia. High prevalences are reported from centres in several regions, including Canada, Australia, New Zealand, the United States and the United Kingdom. The overall mean prevalence is 13.9% and nearly half of those studied had concomitant asthma or eczema. Areas with a low prevalence of rhinitis tended also to have a low prevalence of asthma and eczema.
There is mounting evidence of a rise in the prevalence of allergic diseases, including rhinitis, over recent decades. Lifestyle factors may be important given the high prevalence of rhinitis and other allergic diseases found in westernized English-speaking countries.
What is the mechanism of allergic rhinitis?
Allergic rhinitis is a hypersensitivity response to specific allergens, in sensitized patients that are mediated by IgE antibodies. Sensitized patients with allergic rhinitis have IgE antibodies for specific allergen(s) bound to receptors on the surface of mast cells. On re-exposure to the specific allergen(s), cross-linking of adjacent IgE molecules occurs, and mast cell degranulation (rupture) takes place, releasing a variety of chemical mediators that may be preformed (histamine) or newly synthesized (leukotrienes, prostaglandins)
Histamine causes the cardinal symptoms of allergic rhinitis including sneezing, nasal itching, and runny nose. The nasal congestion is more due to leukotrienes than to histamine. Hence antihistamines are not very good at relieving nasal congestion. A large number of patients with allergic rhinitis will have an increase in sensitivity to allergens after repeated daily exposure; an effect called "priming". At the start of the pollen season, comparatively large doses of pollens are needed to trigger an allergic response but toward the middle and end of the season, patients become extremely reactive to even small amounts of pollen.
How is allergic rhinitis diagnosed?
It should be ascertained whether the allergic symptoms are seasonal or perennial. The exact month of the year that symptoms start could give a clue as to the specific type of pollen involved.
The tree pollen season starts in late winter and usually ends before the grass pollen season in spring. The weed pollen season overlaps with the grass season, usually starting in late spring and extending through to end of summer.
Patients who are allergic to their pets will often deny obvious symptoms related to contact with their own pets. This is due to some sort of tolerance developed due to continuous exposure to the allergen. If they were to go away for two weeks vacation, they might notice immediate symptoms upon their return.
The predominance of nasal symptoms on waking may suggest the diagnosis of house dust mite allergic rhinitis.
- Nasal Examination: Pale, bluish, swollen mucosa (lining).
- Skin prick test should be performed to identify the specific allergen(s) involved, so that the correct avoidance measures can be recommended.
The skin prick test is a sensitive, simple and cheap diagnostic technique.
How is allergic rhinitis treated?
Broadly speaking there are three main options in the treatment of allergic rhinitis:
Total eradication of the allergen is usually not possible, but measures to reduce the allergen in the local environment should be encouraged. The measures to be used will differ depending on the nature of the allergen.
Pollen particles are part of the reproductive mechanism of plants and are an environmental contaminant, which are difficult or impossible to eliminate. Measures, which can help to reduce the exposure, include:
- Keep windows in cars and buildings shut
- Wear glasses or sunglasses
- Avoid open grassy places, particularly in the evening and at night
- Use a car with a pollen filter
- Check the pollen count in the media
- During the peak season take your holidays by the sea or abroad
House dust mites are found in mattresses, pillows, bedcovers, carpets and soft furnishings throughout the home. Optimal conditions for mite growth are achieved through well-insulated, centrally heated homes!
Mattress/bedding barrier intervention has been shown to reduce mite allergen levels and improve clinical symptoms of both rhinitis and asthma.
The major cat allergen is a salivary protein, which is preened on to the fur where it dries into flakes, which become airborne for many hours and are very respirable.
Families with atopic (allergic) members should be advised against furred animals in the home. Psychological factors may render dogmatic statements about removal of a family pet unwise.
Where removal of a pet is not possible, advice can be given to confine the animal outside the house.
Recent studies have suggested that washing the cat (once weekly) when combined with other cleaning measures may effectively reduce airborne cat allergen levels in the home.
Patients need drugs for allergic rhinitis if avoiding the allergen is impossible or fails to control the symptoms.
In recent years, the mainstay of treatment for allergic rhinitis has been the use of topical corticosteroid nasal sprays, and the newer non-sedating antihistamines. These may be highly effective when used either alone or in combination.
Topical sodium cromoglycate represents an alternative anti-inflammatory agent to corticosteroids, particularly in young children.
Topical anticholinergic drugs (e.g. atrovent) and decongestants may have a part to play in defined circumstances.
Corticosteroids and sodium cromoglycate affect the underlying allergic process and should be used as first line treatment for most patients. Compliance may be a problem with cromoglycates, as they need to be used 3-6 times per day.
Antihistamines and decongestants simply relieve symptoms.
Topical decongestants should not be used for more than 5 days because of rebound congestion.
Immunotherapy is the subcutaneous injection of increasing doses of the identified allergen(s).
Both seasonal and perennial allergic rhinitis may, in general, be effectively managed with a combination of allergen avoidance measures plus topical corticosteroids and oral non-sedating antihistamines. There remains a small group of subjects who, despite regular use of medication, continue to have marked symptoms or unacceptable side-effects from their medication. These patients should be offered immunotherapy.
Useful link – JCAAI : Rhinitis