'A diagnosis of idiopathic anaphylaxis is a confession that we do not have a clue, and we should say so' says Dr Harry Morrow-Brown, an allergist of many years' experience. For more of Dr Harry's case histories, check out www.allergiesexplained.com

In finding the cause of anaphylaxis it is most helpful if the patient can tell you what they ate, or what they were doing just before the attack. If they have kept the labels from the suspect food or foods it can be easy to identify the cause, but a detailed history is the most important part of the consultation.

Skin prick testing
Confirmation by skin testing with commercial extracts may be possible, but the cause may be an unusual food for which no test is available. Also commercial testing extracts are not available for everything, and sometimes the allergen gets destroyed in the processing producing a false negative test. Nuts, egg, fish, sesame, sea food and latex are reliable tests, but wheat, milk, and many fruits and vegetables are not. It is simple to mash up some of a vegetable in a drop of saline and prick through it, or squeeze out a little juice, as with potato, and prick through it.

This is when the 'Prick-Prick' test, when you prick the fruit and then prick the patient, can be very helpful, but is seldom possible in a clinic or hospital unless the patient brings the suspect materials at another visit. There is no significant risk of triggering an anaphylactic reaction from a skin prick test, but you should have adrenaline readily available anyway.

Immunological tests
Immunological tests should be very helpful because anaphylaxis is a classical IgE mediated reaction so it should be possible to demonstrate the presence of specific IgE directed at the cause. Obviously an attack should be triggered every time the causative food is eaten, the severity of reaction being modified by the amount ingested.

When there is no suggestive history of a food trigger and all skin tests are negative the situation can be very difficult. Even if Total IgE is found to be high, there is still nothing to indicate which specific allergen is involved, so you have no idea what tests to ask for. As the total IgE is simply the sum of all the specific IgE antibodies in the blood it is possible that when only one allergen is involved the Total IgE may be only slightly over normal, giving a false impression.

This is where the blunderbuss approach of asking for a wide range of tests for specific IgE might pay off, but unless the result is clear-cut and can be confirmed you still cannot advise the patient what food or other allergen they must avoid at peril of their life. A diagnosis of 'idiopathic anaphylaxis' is a confession that we do not have a clue, and we should say so.

Case History

Sandra is 56 and comes from a very allergic family, most of whom I have seen over many years, and she has an identical twin who has very similar problems. Father died of asthma, and another sister, her two daughters, and two grandchildren all have asthma. Sandra has had asthma since infancy, triggered by dust, cats, horses, and birds, and she also has seasonal hay fever, but the respiratory allergies are relatively easily controlled with inhaled steroids and bronchodilators, and occasional oral steroids.

Her major problem is allergy to foods, because since the aged eight she has been subject to attacks of acute colic, diarrhoea and vomiting which were definitely triggered by a variety of foods such as chocolate, mustard, mint, vegetable oils except corn oil, bananas, and sesame. As gut reactions occurred within minutes associations were obvious. Breakfast cereals such as shredded wheat or rice crispies would cause acute diarrhoea in ten minutes.

Since her gallbladder was removed three years ago her food problems have tended to become worse, her stools float and are very malodorous. She had had an anaphylactic reaction within minutes of eating some sesame, and some time later had another attack of anaphylaxis after having liver pate with garlic. As she tolerated liver pate without garlic, garlic was a an obvious possibility.

Fortunately she had been given an Epipen which brought the reactions under control without difficulty, but she had had a fright and wanted to know precisely what to avoid. When seen elsewhere the diagnosis offered was idiopathic anaphylaxis, which she felt was unsatisfactory and sought further advice.

Skin test reactions were +postive for mites, dog +++ , sesame+++, grass pollen+++, and the first ++positive I have ever seen for candida albicans.

She had brought a sample of the garlic pate, and digging a prick test needle into the pate and then pricking her skin with it produced a wheal 20 mm in diameter. The ‘prick- prick test’ can be very helpful when specific skin tests are not available, The prick-prick test was +++ using a clove of raw garlic, and mustard from my kitchen. Her allergy to garlic may have been triggered by having been liberally dosed with 'Liqua Fruta' cough medicine as a child because the active ingredient is garlic, but why she should become dangerously sensitive to it in middle age is a mystery.

Immunology to exclude coeliac disease was negative, but increased gut permeability seems likely. Total IgE was raised at 232 Ku/l (81 is normal limit) Specific IgE for dog, sesame, mustard, and grass pollen were +++, candida was ++, and ++ for grain mix. RAST for individual cereals was positive for wheat, barley, and rice, but negative for rye.

These findings fitted the fact that she could not tolerate a special few foods diet which included rice as the main carbohydrate source. Rice allergy is most unusual in the West, common in the Far East. A course of Fluconazole had no effect, suggesting that the very unusual finding of specific IgE to candida was of no clinical significance.

She remains well on a very limited diet avoiding all known causes of allergic gut reactions and anaphylaxis. This case is presented to demonstrate the importance of the family history and a holistic approach to investigation. The ‘prick-prick’ method of skin testing can be very useful in tracking down the cause, and can demonstrate to the patient what foods must be avoided.

For more of Dr Harry's case histories, check out www.allergiesexplained.com

First published in 2007

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