Allergy or idiopathic anaphylaxis?

In the third of our series on food allergy, Dr Michael Radcliffe explains the cause of anaphylaxis.

Janice, a 35-year-old veterinary nurse, attended for the results of allergy blood tests.

She had experienced an attack of anaphylaxis at a reception for the opening of the new veterinary practice.

The report explained that while she was eating canapes she became intensely itchy, flushed and weak and after a few minutes she briefly passed out. When she came round she was fighting for breath and could not speak.

The paramedics gave IM adrenaline and oxygen and when she reached the A&E department she was hypotensive and wheezy and was given more adrenaline, an IV infusion, hydrocortisone, chlorphenamine and a nebulised bronchodilator. She steadily recovered and was discharged the next morning.

Janice said that nothing like this had ever happened before. Although she suffers from well-controlled asthma and eczema, there has never been any suspicion of food allergy. She suspects that the canapes had contained shellfish, tuna, nuts, sesame seeds and egg. So you requested RAST tests to seafood and nut panels together with sesame seed, milk, egg, wheat and tuna.

These tests were all negative. What should you do next?

An allergy specialist's view
The history and findings at the time of the attack support a diagnosis of anaphylaxis. Particular risk factors include:

  • Unknown causation.
  • Asthma.
  • The severity of the attack.

This patient needs to be advised to carry adrenaline and shown when to use it. Ideally friends and relatives should be similarly instructed and the patient should be advised to join the Anaphylaxis Campaign (www.anaphylaxis.org.uk).

Treatment
If adults carry an adrenaline auto-injector (Anapen, EpiPen), the standard 300 microgram dose will usually be sufficient.

However, a second dose may be required, particularly if the patient is ever at a distance from medical help. So it is sensible to advise that a pair of adrenaline injections should be carried both to provide sufficient treatment.

The patient needs full assessment to establish or exclude food allergic causation. If this is confirmed, allergen avoidance counselling should be arranged with a dietitian.

Diagnosis
Janice's story is based on an actual allergy clinic case. Extensive skin-prick testing to the above-listed foods plus individually tested nuts, fish and shellfish were negative.

Less common food allergens (celery, chick pea, lentil, linseed, lupin flour, mustard, onion, pea, poppy seed and soya) were also tested and these were negative.

The investigation of anaphylaxis reveals no cause in a proportion of cases. These cases are reported as idiopathic anaphylaxis, although the term seems ill-advised. It infers the non-existence of an external trigger.

Retrospective studies report that idiopathic anaphylaxis might account for up to a third of cases of anaphylaxis investigated, depending on the intensity of the investigation.

Further investigation
Janice was asked to make contact with the caterer requesting a copy of the canape menu prior to the next appointment.

An item on the menu 'fillet of lamb with red pepper pesto and thyme blini' added a further possibility. Blini are tiny pancakes, normally made from buckwheat flour.

A small quantity of buckwheat flour was obtained, and a skin-prick test performed.

The outcome was positive and Janice was able to confirm that the blini were made from buckwheat.

Buckwheat is taxonomically unrelated to wheat and its main usage in the UK was in specialty gluten-free products. It was rarely reported as a cause of anaphylaxis in Europe until recently, although it is a common cause of anaphylaxis in Asia.

It is likely that causes of food-induced anaphylaxis will be encountered from time to time.

The cause is obvious in most cases of food-induced anaphylaxis, as one of the major food allergen is likely to be involved (see box).

But with the increasing complexity of large-scale food manufacturing, and with the increasing use of novel foods, identifying the cause of food-induced anaphylaxis in every case is becoming much more of a challenge.

Dr Radcliffe is a consultant in allergy medicine at the Royal Free NHS Trust

Food allergy and Intolerance week runs 21-25 January. For more information see www.allergyuk.org

Main allergens

  • Peanut.
  • Tree nuts.
  • Fish.
  • Shellfish.
  • Milk.
  • Egg.
  • Wheat.
  • Soya.
  • Sesame seed.

References

Kemp S, Lockey R, Wolf B, Lieberman P. Anaphylaxis: a review of 266 cases. Arch Intern Med 1995; 155: 1,749-54.

Radcliffe M J, Scadding G K, Morrow Brown H. Lupin flour anaphylaxis. Lancet 2005: 365: 1,360.

M H Sohn, S Y Lee, K-E Kim. Prediction of buckwheat allergy using specific IgE concentrations in children. Allergy 2003; 58 (12): 1,308-10.

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