Allergic rhinitis is an IgE mediated, type 1 hypersensitivity reaction in the lining of the nose. It is common, affecting around 40% of the population, and the incidence is rising. There are other forms of rhinitis and a classification of rhinitis is found in the diagram below. Note that non-infective non-allergic rhinitis used to be called vasomotor rhinitis.
There are two types of allergic rhinitis: seasonal (Hayfever) and perennial. In the first the symptoms of the condition are present for a period of time and then go away; in perennial rhinitis they are always present.
Grass pollens are the commonest seasonal allergens but tree and fungal allergens are also found. House dust mite, cat and dog dander are the commonest perennial allergens. Occupational rhinitis falls into this group.
Allergic rhinitis is a risk factor for developing asthma and treating moderate to severe allergic rhinitis is important in the management of asthmatic symptoms.
This diagram is one schematic representation of the classification of rhinitis.
Non-infective, non-allergic rhinitis (bottom right of the classification) includes such conditions as hormonal rhinitis (e.g. during pregnancy), hypothyroidism, rhinitis of the elderly, smoking related, and drug-induced rhinitis.
Drug-induced rhinitis is called rhinitis medicamentosa. The most notable causes are over the counter drugs such as oxymetazoline and xylometazoline. These are the active ingredients in Sinex and Otrivine and are used by patients who have a blocked nose to get decongestion and relief. They are very effective but, if used beyond about ten days, cause a rebound congestion and hypersensitivity in the mucosa. This is rhinitis medicamentosa.
Many other drugs can have an effect on the nose. For example, 𝛽-blockers, ACE inhibitors, and the 𝛼-adrenergic blockers used for benign prostatic hypertrophy.
The symptoms of allergic rhinitis are sneezing, nasal itching, clear nasal discharge and nasal obstruction. These occur on exposure to the allergen. In seasonal allergic rhinitis, these symptoms are pronounced during the summer and when the grass has been cut. People allergic to cats get the same symptoms when a cat is or has been, present in a room.
Physical signs include a pale, swollen, bluish nasal mucosa with thin clear nasal discharge.
Note that although nasal polyps are sometimes found in allergic rhinitis it is not true that most polyps are of allergic origin.
A history and clinical evaluation are very important in establishing the diagnosis. Laboratory tests must only be interpreted in the light of these.
There are two tests that are done routinely:
1. Skin prick tests
2. RAST (a blood test)
Skin prick testing is done by gently pricking the skin through a drop of purified allergen. This is usually done on the volar aspect of the forearm. A number of allergens are tested at one time and the flare and wheal response compared with control substances. If an allergy is present a large flare and wheal will result under the test substance.
Skin testing is cheap and gives a quick result that the patient can see. It must only be done in places that have adequate resuscitation equipment as there is a very small chance of anaphylaxis.
RAST (radioallergosorbent test) is performed on a sample of venous blood. The details of this are not important. It is easy to do but takes time to give a result and is more expensive than skin testing.
The principles of management are quite simple:
1. Avoid the allergen
2. Use antihistamines by mouth or spray, and avoidance
3. Use nasal steroid sprays and avoidance
4. Use antihistamines and nasal steroids and avoidance
The decision as to which form of therapy is used is dependant on the patient's response. If avoidance alone is inadequate then antihistamines have to be tried as well. If this is inadequate, change to nasal steroids and avoidance and if this does not work all three therapies have to be used.
Desensitisation can be done for patients in whom the above has failed or in those with life-threatening allergy e.g. to bee sting. It is a successful therapy but takes a long time to do.
Surgery can't cure allergy but it can relieve nasal obstruction when nasal steroids have failed.