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Idiopathic anaphylaxis


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A fifteen year old boy came into ED, brought in by his parents after having to use his EpiPen at home. He was at school, he was well in the morning. Suddenly while walking between classes he started to feel nauseous, sort of breath and tight chested. Once again he was having an anaphylactic reaction, but he did not know what he was reacting to.



Anaphylaxis is a common severe allergic reaction to an allergen. IgE binds to the allergen which causes degranulation of mast cells and basophils leading to histamine release.  This in turn causes smooth muscle constriction and bronchoconstriction as well as angioedema. This is a type 1 immunological reaction.

This reaction leads to facial swelling, bronchoconstriction, airway obstruction, rash, vomiting, diarrhoea and fluid redistribution leading to shock and respiratory failure. Anaphylaxis is a life-threatening medical emergency and needs prompt treatment as well as education to prevent further anaphylactic attacks. So the prevention of anaphylactic shocks is highly important, and usually this can be done by tracing common allergens that the patient was exposed to right before they develop a reaction. However, in some cases this is more difficult to determine and may not be obvious.

In our case there was no identifiable allergen at all.


Idiopathic anaphylaxis

Idiopathic anaphylaxis is a condition where patients develops an anaphylactic reaction without a causative agent. The patient develops an anaphylactic reaction without any form of trigger. This can be dangerous, as patients can spontaneously develop anaphylaxis without any warning, putting them in life threatening situations regularly and without warning. It is unclear what causes this and although patients are commonly very atopic and will have other atopic conditions and allergies.



Treatment for idiopathic anaphylaxis is the same as for any other cause of anaphylaxis in the acute setting. Patients need treatment with adrenaline and steroids. However, in the long term they need to be well educated and prepared, including education on what anaphylaxis is and how important it is, using EpiPen’s and how important it is to always carry one in case of a reaction developing.

The child in out case, underwent multiple allergen and immunological investigations and although multiple allergens were identified, he continued to have anaphylactic reactions without apparent triggers.


Key learning points

  • Anaphylaxis can occasionally be idiopathic although this is rare
  • Idiopathic anaphylaxis has the same pathology and presentation to allergen mediated anaphylaxis
  • Patients with idiopathic anaphylaxis need the same acute treatment
  • Long term treatment involves a lot of education around the condition

About the authors

  • Abbey Ward is a a foundation doctor, interested in teaching, paediatrics, emergency medicine and intensive care, but she has not decided what to do when she grows up! You can find her on twitter as @AbbeyWardDr


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