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Idiopathic anapylaxis: allergy without a cause

 - Typical symptoms of anaphylaxis and common triggers

 - Identifying and ruling out the causes of an anaphylactic reaction

 - Diagnosing and managing idiopathic anaphylaxis


Anaphylaxis is the most extreme form of severe allergic reaction, which can be life-threatening and require emergency medical treatment. It can affect patients of any age, sex, race and stature. Allergic reactions occur when the body's immune system reacts inappropriately in response to the presence of a food or substance that it wrongly perceives to be a threat. When this happens, chemicals including histamine are released from cells in the blood and tissues where they are stored. These can cause severe symptoms, including:
  - Pruritus and urticarial.
  - Swelling in the throat and/or mouth.
  - Difficulty breathing.
  - Severe asthma.
  - Severe abdominal pain, nausea and vomiting.

In extreme cases there can be a dramatic fall in blood pressure (anaphylactic shock). The person may become weak and floppy and this may lead to collapse and unconsciousness. An early symptom may be a sense of foreboding or that something terrible is about to happen.

Symptoms of anaphylaxis typically start within seconds or minutes of exposure to the food or substance, but on rare occasions there may be a delay of an hour or more. The most common causes of anaphylaxis include foods such as peanuts, tree nuts (including almonds, hazelnuts, walnuts, Brazils and cashews), milk, eggs, shellfish, fish, sesame seeds and kiwi fruit. Many other foods have also been known to trigger anaphylaxis. Non-food causes include wasp or bee stings, natural rubber latex, and certain drugs such as penicillin.

Identifying triggers and ruling out causes

If you think a patient is showing symptoms of anaphylaxis, you should advise them to see their GP as soon as possible and seek referral to an allergy clinic. Even apparently mild cases need to be medically assessed because the next reaction could be more severe.

  - Once referred, possible triggers can begin to be eliminated. All substances, even if previously safely consumed, should be considered, for instance:

  - Food. Should be considered a prime suspect, especially if eaten a few minutes before the start of an attack. The most common food triggers are shellfish, fish, peanuts, tree nuts (such as cashews, walnuts or Brazils), milk, eggs and wheat, but many others are also implicated on rare occasions. If a particular food is suspected, but skin or blood tests are unexpectedly negative, the consultant may suggest an oral food challenge test to eliminate this food from the investigation.

  - Prescribed drugs. Any medication taken for years may suddenly cause anaphylaxis. If skin tests are not available for a suspected medication, the patient may be required to exclude it temporarily and then take a test dose. This must be done under supervision in hospital.

  - Other substances. For example, insect stings and latex.

However, the cause of the problem may be less obvious. A few examples are given below.


The seeds from some varieties of lupin are milled to make flour, which is used in baked goods such as pastries, pies, pancakes and in pasta. Allergy to lupin has been recognised for some time in mainland Europe, where lupin flour is used fairly commonly in food products. Any patient suffering an allergic reaction to a food containing lupin flour should consider it is the possible culprit. By law, lupin must be declared in the ingredients list when present in pre-packed food.

Natural rubber latex (NRL)

This is found in thousands of everyday consumer and healthcare items. Reports of allergy to natural rubber latex have become increasingly common over the past 25 years and especially among healthcare workers. Many people associate allergy primarily with food - but latex should be considered as a possible cause if a reaction occurs during an operation, during a medical or dental procedure, or just after handling an item made of soft rubber.


For a small minority, anaphylaxis can occur while taking exercise. When this happens, a possible explanation is food-dependent, exercise-induced anaphylaxis (FDEIA). Anaphylaxis occurs when an unsuspected food allergen is eaten and exercise is taken within an hour or two. Wheat is often the culprit food, although others including shellfish are sometimes implicated.

When is anaphylaxis termed idiopathic?

Anaphylaxis is a frightening event for any patient, coming on suddenly and progressing rapidly. If, after a diagnostic investigation, the doctor is unable to identify a trigger for a patient's allergy, the term idiopathic anaphylaxis is used.  

The symptoms of idiopathic anaphylaxis are no different from those in cases where the trigger is known and, as with all cases of anaphylaxis, idiopathic anaphylaxis has the potential to be life threatening.

While the possibility of an overlooked allergy should always be borne in mind, the name idiopathic anaphylaxis infers that there is no external trigger and that the cause is a temporary increase in the reactivity of the immune system. When attacks are occurring frequently, a few weeks of treatment with an oral steroid may be indicated. This increased reactivity usually clears up within a few weeks or months, although in some cases the condition may take a year or two to settle.

Once a diagnosis has been made, the patient is likely to be prescribed injectable adrenaline such as EpiPen, Jext or Emerade. Most patients find these injectors easy to use but they must be trained how to use them, and nurses should strongly advise patients to make their injector immediately available at all times.

How you can help

In your role as nurse you can help primarily by being aware of the symptoms of anaphylaxis and its possible causes, both internal and external, and offering information to those potentially affected. Be vigilant for persistent cases where no discernable trigger is identified, and encourage those affected to visit their GP and ask for a referral to an allergy specialist for further investigation.

It may also be useful to encourage these patients to keep a diary and detailed account noting time, date, location, consumption and activity in the hours leading up to any reactions. All these details can help to build a picture of the problem and possibly identify a common thread.
In summary, nurses should:

  - Be aware of the symptoms and their progression.

  - Encourage patients to carry their prescribed medication- a particularly important point for idiopathic sufferers as they are even less likely to be able to predict where and when a reaction may occur.

  - Learn how to instruct patients concerning how and when to use their adrenaline auto-injector.

  - Learn and educate others concerning the correct emergency response for anaphylaxis, including the ABCDE (airway, breathing, circulation, disability, exposure) approach.


Anaphylaxis Campaign
AllergyWise online course for Healthcare Professionals
01252 542029
NICE Guidance on anaphylaxis