Anaphylaxis Health Article

Definition

Anaphylaxis is a severe, sudden, and potentially fatal allergic reaction to a foreign substance or antigen that affects multiple systems of the body.

Description

Anaphylaxis is a severe, whole-body allergic reaction. After initial exposure to a substance such as wasp sting toxin, the allergic child's immune system becomes sensitized to that allergen. On a subsequent exposure to the specific allergen, an allergic reaction, which can involve a number of different areas of the body, occurs. Anaphylaxis is thought to result from antigen-antibody interactions on the surface of mast cells, connective tissue cells that are believed to contain a number of regulatory, or mediator, chemicals. Specifically, an immunoglobulin antibody protein, IgE, is produced in response to the presence of the allergen. IgE binds to the mast cells, causing them to suddenly release a number of chemicals, including histamine, heparin, serotonin, and bradykinin. Once released, these chemicals produce the bodily reactions that characterize anaphylaxis: constriction of the airways, causing wheezing and difficulty in breathing; and gastrointestinal symptoms, such as abdominal pain, cramps, vomiting, and diarrhea. Shock can occur when the released histamine causes the blood vessels to dilate, which lowers blood pressure; histamine also causes fluids to leak from the bloodstream into the tissues, lowering the blood volume. Pulmonary edema can result from fluids leaking into the alveoli (air sacs) of the lung.

Substances that can trigger an anaphylactic reaction include:

• insect stings from hornets, wasps, yellow jackets, honey bees, or fire ants
• medications, including penicillin, cephalosporin, anesthetics, streptokinase, and others
• foods (ingesting even tiny amounts or simply being near the offending food), including peanuts, tree nuts (such as walnuts or almonds), fish, shellfish, eggs, milk, soy, and wheat
• vaccines, including allergy shots and egg- and gelatin-based vaccines
• hormones, including insulin and possibly progesterone
• rubber latex products
• animal and human proteins, including seminal fluid and horse serum (which is used as snake anti-venom)

Anaphylactoid (meaning "anaphylactic-like") reactions are similar to those of true anaphylaxis but do not require an IgE immune reaction. These are usually caused by direct stimulation of the mast cells. The same chemicals as with anaphylaxis are released, with the same effects, so the symptoms are treated the same way. However, an anaphylactoid reaction can occur on initial exposure to an allergen as well as on subsequent exposures, since no sensitization is required.

There is also a rare kind of food allergy, called exercise-induced allergy, that is caused by eating a specific food and then exercising. It can produce itching, lightheadedness, hives, and anaphylaxis. The offending food does not cause a reaction without exercise, and, alternately, exercise does not cause a reaction without ingesting the food beforehand.

Demographics

Although likely an underestimate, about 10,000 cases of anaphylaxis occur per year in North America, with about 750 fatalities a year. The exact prevalence of anaphylaxis is unknown, because milder reactions may be attributed to asthma attacks or sudden cases of hives, and more serious or fatal episodes might be reported as heart attacks, as the initial symptoms of hives, asthma, and swollen throat can fade quickly.

Causes and symptoms

The symptoms of anaphylaxis may occur within seconds of exposure, or be delayed 15 to 30 minutes and sometimes even an hour or more later, if the allergen is aspirin or other similar drugs. The sooner the symptoms occur after exposure, the more severe the anaphylactic reaction is likely to be.

The first symptoms of an anaphylactic reaction are associated with the skin: flushing (warmth and redness), itching (often in the groin or armpits), and hives. These symptoms are often accompanied by anxiety; a rapid, irregular pulse; and a sense of impending doom. Then the throat and tongue swell, the voice becomes hoarse, and swallowing and breathing become labored. Symptoms of rhinitis or asthma may also occur, causing a runny nose, sneezing, wheezing, and abnormal high-pitched breathing sounds, further worsening the breathing problems. Gastrointestinal effects may also develop, including vomiting, diarrhea, and stomach cramps. The child may be confused and have slurred speech. In about 25 percent of the cases, the chemicals flooding the blood stream will cause a generalized opening of capillaries (tiny blood vessels), resulting in a drop in blood pressure, lightheadedness, and even a loss of consciousness, which are typical symptoms of anaphylactic shock. The child may exhibit blueness of the skin (cyanosis), lips, or nail beds.

After the original symptoms occur, there are three possible outcomes:

• The symptoms may be mild and fade spontaneously or be quickly ended by administering emergency medication. The anaphylactic episode is over for that particular exposure.
• After initial improvement, the symptoms may reoccur after four to 12 hours (a late phase recurrent reaction) and require additional treatment and monitoring. Late phase reactions occur in about 10 percent of cases.
• The reaction may be persistent and severe, requiring extensive medical treatment and hospitalization. This condition occurs in about 20 percent of cases.