If it can threaten life, we can stop its most serious manifestations but also prevent it. Head of the pulmonology department at Montpellier University Hospital, Professor Pascal Demoly tells us what you need to know.
Paris Match. What does this term refer to?
Pr Pascal Demoly. A form of so-called “immediate” allergy which is a violent reaction of generalized hypersensitivity, of rapid onset (a few minutes to a few hours, fifteen minutes on average) and which is life-threatening. It is marked by: 1. Sudden onset of upper or lower airway spasm. The air remains “trapped” in the lungs, without being able to leave or enter, a double sensation perceived by the patients. 2. A massive vasodilatation of the vessels at the origin of a major hypotension which can defuse the heart. 3. Extreme weakness with confusion and sometimes coma. 4. Very often (90% of cases) there is associated diffuse vascular edema called angioedema of Quincke. It can affect the skin (erythema, urticaria) and/or the digestive tract (intense pain, nausea, vomiting, diarrhea) and/or the larynx, the most feared condition (risk of asphyxiation).
What are its incidence and triggers?
Nearly 3% of French people have at least one anaphylactic event during their lifetime. The annual incidence (increasing) varies according to the studies from 1 to 8 cases per 100,000 inhabitants. It affects both children and adults of both sexes. A ground called “atopic” (family of allergic people, certain biological predispositions) favors it. It is triggered by an allergen which, in order of frequency, can be a drug (antibiotic, curare, chemotherapy, immunotherapy, etc.), a food (seafood, nuts, dairy products, etc.) or a hymenoptera (bee, wasp , hornet, ant) especially in summer. A multitude of other products (latex for example) are more rarely the allergen. Vaccines are only exceptional (1 case out of 100,000).
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In subjects at risk or predisposed, the saving gesture is a self-injection of adrenaline
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What are the biological mechanism and the major risk?
Allergic anaphylaxis sets in in two stages: 1. A first contact with the allergen, without symptoms, sensitizes the person by inducing in them the secretion of IgE antibodies (by white blood cells called “plasmocytes”) which will attach to certain immune cells called “mast cells”. 2. During a second contact with the allergen, under the action of IgE, the mast cells release enormous quantities of active substances (especially histamine) having a double effect: dilate the vessels and “spasm” the bronchi. The extreme version is anaphylactic shock which combines vascular collapse and acute respiratory distress with multiple organ failure. It is estimated that about 10% of these shocks lead to death. 3. Non-allergic anaphylaxis (20% of cases) also exists, toxic (by overdose) or by dysregulation of mast cells.
How is anaphylactic shock treated?
The only urgent treatment worthwhile is the intramuscular injection of adrenaline. It acts immediately against the dilation of the vessels which it reinvigorates and against the spasm of the bronchi which it releases. In subjects at risk or predisposed, the life-saving gesture (which can be done through pants) is self-injection in the outer middle third of the thigh using an adrenaline pen. Three doses exist: 0.15 mg in children, 0.3 mg and 0.5 mg in adults. Without improvement within five to ten minutes, they must be repeated. It is absolutely necessary to avoid administering corticosteroids as first intention (effect too delayed) and to wait to see what happens, as some practitioners continue to do. Without a doctor present, call 15. Position the person in shock on their back and hold their legs in the air in the event of severe hypotension, put them on their side if they vomit, place them semi-sitting if they are breathing wrong. Remove the allergen if it has been identified (insect, food).
Also read. Food allergies: what treatment?
And preventively?
Desensitization is sometimes possible, especially against Hymenoptera (100% cure against wasp stings, 80% against bee stings). Predisposed subjects should always carry an adrenaline pen with them. I will mention three: Emerade, the most practical (the only one equipped with a long needle which secures intramuscular administration in a single gesture, with three doses available). And two other good alternatives: Jext and Epipen.