What is Exercise-Induced Anaphylaxis ?
Exercise-induced anaphylaxis (EIA) is a rare disorder in which anaphylaxis is triggered by physical activity. The symptoms may include :
- abdominal cramps
- low blood pressure
EIA symptoms can progress to full anaphylaxis if the person continues with the exercise. Cessation of physical activity generally immediately improves symptoms. A vast range of physical activities can trigger the reactions, including mild effort such as a stroll. It is generally triggered by exercise with more cardiovascular demand, in the first 30 minutes after starting. The same exercise may not always cause symptoms in the same person. People with EIA represent 5% to 15% of all anaphylactic cases.
Types of EIA
There are two subtypes of EIA. In the first type, there is no known trigger other than physical effort. In the second type, the symptoms will occur when specific foods are eaten several minutes to a few hours before exercise, but there are also reports of cases where the symptoms occurred by eating the trigger foods after exercise. This subtype is called Food-Dependent Exercise-Induced Anaphylaxis (FDEIA). The types of foods that trigger symptoms are often allergens that are common in a given population. For Europeans for instance common trigger foods are tomatoes, cereals and peanuts.
There is no known cure for EIA, but the condition can be managed. People with EIA should avoid physical effort outside when the weather is very cold, hot or humid, or, with those who have a seasonal allergy, during pollen season. Protection with antihistamines, montelukast or mast cell stabilization agents like omalizumab (Xolair) can also prevent symptoms.
In people with FDEIA, avoidance of the trigger food a few hours before and after exercise will prevent symptoms.
What is the cause of EIA ?
The mechanisms of EIA and FDEIA are not quite understood. The general consensus is that histamine release is a key component. There are a few hypotheses :
- Increased gastrointestinal permeability : exercise increases absorption from the gastrointestinal tract. In people with FDEIA, this could promote more allergen entering their blood stream when exercising and thus triggering anaphylaxis.
- Aspirin and NSAIDs : Aspirin / NSAIDs are known to increase gastrointestinal permeability and antigen uptake. In people with FDEIA, this could be an additional factor in more allergen entering the blood stream.
- Increased tissue enzyme activity : some enzymes in the intestinal mucosa are known to be activated by exercise and aspirin. These enzymes are known to promote IgE-mediated allergic reactions
- Blood flow redistribution : Exercise changes blood circulation from inactive to active tissues. This could redistribute recently-digested allergens from the gut to active tissues and bring them in contact with mast cells in those tissues.
- Endorphin release : Exercise is known to promote the release of endorphins. Endorphins promote mast cell degranulation.