Anaphylaxis

Anaphylaxis is a potentially fatal, serious allergic reaction that occurs very quickly and involves the whole body. After being exposed to a substance like bee venom, a person’s immune system becomes sensitized to that allergen. In unusual situations, when that person is exposed to that allergen again, an overwhelming allergic reaction may occur.

Anaphylaxis may occur in response to any allergen, but the most common causes are allergies to latex; drugs, particularly penicillin; foods, such as peanuts, fish, shellfish, milk and eggs; and bites and stings from insects, including bees, yellow jackets, fire ants and wasps. Some people may have an anaphylactic reaction with no identifiable cause. Some drugs, including dye used in CT scans and other X-rays and nonsteroidal anti-inflammatory drugs, may cause a reaction similar to anaphylaxis on initial exposure. This is called an ‘anaphylactoid reaction’ and is usually a toxic reaction rather than the true allergic reaction of an anaphylactic reaction. The symptoms and treatment for both types of reactions are identical.

Anaphylaxis typically occurs within minutes of exposure to a particular allergen. Symptoms include skin reactions usually involving the entire body (e.g., hives, itching, flushed or pale skin), tightening of the airways and swelling of the tongue or throat, a weak or rapid pulse, dizziness or fainting, and nausea, vomiting and diarrhea. Less common symptoms include abdominal pain or cramping, anxiety, confusion, wheezing and slurred speech.

It is unknown exactly how many people are at risk of anaphylaxis, but estimates range up to more than 40 million people with allergies severe enough to put them at significant risk. It is estimated to be fatal in one to two percent of all cases. While fatal anaphylaxis can strike individuals of any age, certain interesting patterns are recognized. Fatal anaphylaxis to cow’s milk affects mostly school-age children. Fatal peanut reactions affect mostly adolescents and young adults. The most common causes of fatal anaphylaxis in adults over 50 are IV contrast dyes and medications.

In one study that examined the cases of 25 victims of fatal anaphylaxis, only one-third of victims were known to have a history of a previous allergic reaction. Even in patients with known past reactions, the severity of previous reactions does not necessarily predict the severity of future reactions. Only a small amount of allergen is required to cause death. For example, the typical fatal dose of nuts is only about one gram and most insect sting fatalities result from a single dose.

Certain people are at greater risk for anaphylaxis. The most important risk factor for death from food-related anaphylaxis is asthma. People who remain upright during anaphylaxis rather than lying down are at greater risk for death.

The most important factor in preventing death is the early recognition of anaphylaxis. Next, epinephrine should be administered as quickly as possible. Individuals who received epinephrine within 30 minutes of exposure have increased survival. This typically requires getting access to emergency medical services. Many individuals who have had previous anaphylaxis reactions carry an EpiPen® with them at all times–this is an individual dose of epinephrine which can be quickly administered by the victim or a bystander while waiting for medical attention. Each dose of epinephrine–also known as adrenaline–is effective for 10 to 15 minutes. Finally, people with a history of anaphylaxis should avoid exposure to the allergic trigger.

Dr. McMahon, a graduate of Yale University and the University of Pittsburgh School of Medicine, is board certified in Internal Medicine. She is a member of the American College of Physicians and the Allegheny County and Pennsylvania Medical Societies. She is in solo practice in the North Hills of Pittsburgh.