Allergic Rhinitis

Topic Highlights

●    Allergic rhinitis is a collection of symptoms arising due to allergy which predominantly affects the nose and eyes.

●    It is often caused by airborne particles of dust, dander, or plant pollens.

●    This presentation explains the types of allergic reactions, the pathophysiology of allergic rhinitis, its symptoms, risk factors, diagnosis, and treatment.

Transcript

Allergy is a type of hypersensitive reaction to normally harmless proteins or chemical substances. Allergic rhinitis or hay fever is one of the most common allergic conditions. It is caused by an allergy to pollens, grass or other substances in our environment, and usually occurs during the spring and summer months.

The immune system is made up of a network of cells, tissues and organs that work together to protect our body against foreign invading substances or antigens. Leukocytes or white blood cells are part of this defense mechanism. The types of leukocytes are Agranulocytes and Granulocytes. Agranulocytes are grouped into the phagocytes and lymphocytes. The phagocytes engulf the invading organisms to destroy them. The lymphocytes help the body remember and recognize invading organisms, in a process known as sensitization.

When an antigen is detected, the sensitized lymphocytes produce antibodies, which are specialized proteins that lock onto specific antigens like a key and a lock. Once the antibodies are produced they are always present in the body. When this antigen invades the body again, the antibodies recognize the antigen and attach to it. The T helper cells, which are part of the immune system, destroy these antigens to which the antibodies have attached.

T cells also signal other cells such as phagocytes to destroy the antigen. The T helper cells in turn release a chemical called interleukin 4 (IL4), which activates the B lymphocyte cells to produce protective antibodies. These antibodies attach themselves to the receptors present on the mast cell. These cells release histamine and various other chemical substances, which help destroy the antigens. The response is specific to a particular antigen. It manifests within a few minutes of exposure to the antigen.

But an individual develops allergic response to inappropriate stimulus. This is the only type of hypersensitive reaction that is mediated by the immunoglobulin E or IgE. In the case of allergy, when a person becomes sensitized to a harmless substance such as pollen, on a second exposure, the antigen causes cross-links of various IgE antibodies on the mast cells. These cells release histamine and various other chemical substances, which mediate allergic reactions.

Inhalation of spores, pollens, animal dust, mite or dust from the environment can cause allergic rhinitis. The pet's hair, dander and saliva are known allergens. A family history of allergies is an important risk factor. Weather and pollen count are also important factors. Food material such as milk, egg, peanut, fish, shellfish, soy and wheat may also cause allergic reactions.

Allergic rhinitis becomes worse if the pollen count is high. Pollen count is higher during early evenings on sunny days. Humidity and wind help spread pollen far and wide.

Allergic reactions can be classified based on the type of the allergen:

●    Dust allergy is a condition that occurs when the patient is allergic to the fine dust particles floating in the air. These  can be pollen, dust, etc.

●    Pet allergy is a condition in which the pet's fur or feather is the allergic agent.

●    Skin allergy causes inflammation of the skin when it comes in contact with the allergic agent. This is often called  contact dermatitis where the patient develops redness, swelling and pain at the site of the skin which came in contact  with the agent like a new pair of shoes, or gloves etc.

●    In case of food allergy, the patient develops allergic reaction such as rashes, itching skin, and anaphylaxis (a life  threatening allergic reaction).

Patients usually complain of sneezing within a few minutes of exposure to the allergic agent. A mild condition is characterized by short spells of runny nose and watery eyes. This is followed by profuse watery nasal discharge and nasal obstruction. Patients also complain of nasal and eye irritation. Severe conditions are characterized by severe symptoms, which are persistent, lasting for several days or even weeks.

Patients may experience facial pressure and pain due to chronic congestion. It may also affect the sense of smell and taste. Skin beneath the eye may turn bluish. Patients may also suffer from sleeplessness and irritability. Severe allergy can progress to eczema, asthma, urticaria and lastly anaphylaxis.

Anaphylaxis is a severe life threatening allergic reaction affecting many organs of the body. It starts within a few minutes to hours after exposure to the agent. The patient develops a tingling sensation, itching, a metallic taste in the mouth. He/she may also develop a swelling of the mouth and throat, difficulty in breathing, vomiting, diarrhea, a decrease in blood pressure and even a loss of consciousness.

If the allergy is due to seasonal allergens such as pollen, grass or weeds the symptoms may occur during those seasons. If the allergy is due to indoor allergens such as dust mites, cockroaches, mould or pet dander, symptoms may be experienced year-round.

To diagnose allergic rhinitis, the doctor takes the patient's medical history, symptoms and conducts a physical examination. The doctor may also inquire about a family history of asthma. A nasal smear may also be recommended.

The doctor may recommend skin tests. During skin testing, small amounts of purified allergen extracts are pricked into the skin of the arm or upper back and observed for signs of an allergic reaction. Blood tests may be done to measure the amount of the IgE antibodies. High eosinophils may suggest an allergic condition.

Drugs like antihistamines give symptomatic relief to the various symptoms produced by histamine. Antihistamines are available as tablets or nasal sprays. They work by blocking histamine. They are effective in treating symptoms such as sneezing, watery eyes, itching, and runny nose but may not be effective in treating congestion. Antihistamines such as cetirizine and fexofenadine do not cause much drowsiness. Others, such as diphenhydramine, chlorpheniramine and clemastine, cause drowsiness. Patients who take them are advised not to drive or operate heavy machinery.

Decongestants give relief to a stuffy nose in seasonal allergic cases. Decongestants are often combined with antihistamines. These are available as tablets, liquids and nasal sprays. Oral decongestants include pseudoephedrine. Nasal decongestants include phenylephrine and oxymetazoline. Oral decongestants should be used with caution in patients suffering from hypertension as these may elevate blood pressure or worsen the symptoms of prostate enlargement. Continuous use of nasal decongestion spray may cause the return of the symptoms.

Patients with seasonal and perennial allergic response can use a nasal solution or spray called cromolyn sodium, which blocks histamine channels. This is more affective before the onset of symptoms. Nasal atropine is available as a prescription nasal spray. Ipratropium bromide helps relieve a severely runny nose by preventing the glands in the nose from producing excess fluid. It is not effective in treating the other symptoms. Mild side effects include nasal dryness, nosebleeds and sore throat.

Steroid injections may be administered for short-term treatment, usually in an emergency. Immunotherapy may be considered in case of long-term allergic rhinitis. The patient receives regular shots of purified allergen extracts over a few years. This helps to desensitize the patient, thereby decreasing the dependence on medications.

Maintaining a dust free environment is a critical step in preventing allergies. Routine cleaning of the bedroom, vacuuming, and using a wool-free mattress and linen helps to create a dust free environment. One should avoid carpeting rooms. It is advisable to keep furniture to a minimum. Children who are allergic to dust should not be given stuffed toys or toys which can accumulate dust on them. Avoid pets if allergic to pet dander. Food allergy patients have to avoid substances to which they are allergic.

For most, the best way to manage allergic reactions is to prevent them, which is possible by the avoidance of the allergen.