Exercise Induced Anaphylaxis

Exercise induced anaphylaxis is anaphylaxis triggered by physical exertion with no food or drug trigger needed. Episodes occur during or soon after exercise, and the same exercise is sometimes tolerated on other days.

Pathophysiology. The mechanism is unclear. Exercise may raise plasma osmolality, shift blood flow, lower the mast cell threshold and increase tissue transglutaminase activity. Heat, humidity, cold, pollen season, menstruation and drugs (aspirin and other non-steroidal anti-inflammatory drugs) act as cofactors.

It is uncommon and more frequent in young adults and women. Episodes may come in a cluster and tend to fade over years.

Many patients later prove to have a food cofactor that was not recognised at first.

• Warmth, itching and flushing during exercise
• Large urticarial wheals that merge, and angio oedema
• Throat tightness, wheeze, stridor
• Hypotension, collapse and loss of consciousness
• Gastrointestinal symptoms: cramps, vomiting, diarrhoea
• Onset usually after 5 to 30 minutes of exertion
• Different from cholinergic urticaria, which has small (1 to 3 mm) wheals and seldom causes collapse

• History: type, intensity and duration of exercise, timing, meals before exercise, drugs, climate, and menstrual cycle.
• Serum tryptase within 1 to 2 hours of an episode and a baseline value later.
• Skin prick test and specific IgE to foods and omega-5 gliadin to exclude food dependent disease.
• Exercise challenge (treadmill, with resuscitation equipment) is of limited yield, because it is often negative.
• Exclusion of other causes: cardiac testing (ECG, echocardiogram, exercise test), spirometry and exercise challenge for bronchoconstriction, and mast cell disease workup.

Differential diagnosis.

• Food dependent exercise induced anaphylaxis
• Cholinergic urticaria
• Exercise induced bronchoconstriction
• Cardiac arrhythmia and cardiomyopathy
• Idiopathic anaphylaxis
• Mastocytosis, cold urticaria, solar urticaria

• Acute episode: stop exercise, lie flat with legs raised, and give adrenaline 0.5 mg intramuscularly (children 0.01 mg/kg, maximum 0.5 mg) into the anterolateral thigh, repeated after 5 minutes if no improvement, plus oxygen and intravenous fluids, and observation for at least 6 hours.
• Adrenaline auto injector carried during exercise: 150 microgram for 7.5 to 25 kg, 300 microgram for 25 to 50 kg, 500 microgram for over 50 kg, with a written action plan and training.
• Prevention: exercise with a companion who knows the plan, stop at the first itching or flushing, and avoid exercise in extreme heat, cold or humidity and in high pollen counts.
• Avoid cofactors: food in the 4 to 6 hours before exercise if food is implicated, alcohol, aspirin and other non-steroidal anti-inflammatory drugs.
• Antihistamine: cetirizine 10 mg orally once daily in adults may reduce minor symptoms, but does not prevent anaphylaxis.
• Omalizumab is used in specialist care for severe recurrent episodes.
• Medical alert: a bracelet or card with the diagnosis.

Special groups.

• Athletes: work out a training plan with an allergist, since complete avoidance of exercise is rarely needed.

Monitoring. Review every 6 to 12 months. Symptom diary and episode count. Check auto injector dose and expiry.

Referral and escalation. Refer to allergy and, if cardiac cause is possible, to cardiology. Emergency for collapse, airway swelling or wheeze.