Food-allergy-FINAL.mp3. Duration: 0:07:39 START AUDIO

Transcription

1 BMJ LEARNING VIDEO TRANSCRIPT File: Duration: 0:07:39 Food-allergy-FINAL.mp3 START AUDIO Adam Fox: Food allergy is an inappropriate immune response to food. Our immune systems should ignore food completely, but sometimes, inappropriately, they react. Food allergy is pretty common in the UK; in children, for example, it affects 6 to 8%. However, most food allergy is outgrown, so by adulthood it only affects about 1%. There are two common types of food allergy. The first is IgEmediated or immediate-type food allergy, when reactions happen very quickly after the food is consumed, due to the release of histamine and the symptoms that spring from that. The other type of food allergy is non-ige-mediated or delayedtype allergy. This involves the slow-acting cell-mediated part of our immune system and can cause more chronic symptoms, such as eczema, diarrhoea, reflux, colic, and even more unusually, constipation or faltering growth. Most food allergy is caused by a very small number of allergens. With immediate-type allergy, the most common allergens are milk, egg, peanuts, and less commonly tree nuts, fish, soy, wheat, sesame, and kiwi. With delayed-type allergy, it s milk and soy allergy that s most common, and this is most commonly an issue during early infancy. Allergy to milk, to egg, to wheat, and soy are most commonly outgrown during

2 early childhood, whereas allergies to peanuts, tree nuts, fish, and shellfish tend to persist through into adulthood. IgE-mediated or immediate-type food allergies typically present very quickly after the food has been consumed, usually within just a few minutes. Symptoms will usually be urticaria, itchiness, angioedema around the mouth, but in severe cases it may involve features of anaphylaxis. Anaphylaxes are potentially life-threatening reactions that have either cardiovascular or respiratory features. Typically, in adults a severe reaction will involve hypotension, confusion, dizziness, and collapse, whereas in children typically severe reactions have more of a respiratory component, so difficulty in breathing, stridor, or wheeze. Anaphylaxis is a medical emergency and needs prompt treatment with intramuscular adrenaline. With non-ige-mediated allergy it can be much more difficult to make a diagnosis. The symptoms don t happen immediately after the food is consumed and sometimes they may happen many hours later. In reality, in infancy when most delayed allergy occurs, the symptoms are simply chronic whilst the child is continuing to consume the food that s the problem usually milk. There are a number of features in the history that allow you to separate out the many infants who will present to you with colic, reflux, diarrhoea, eczema, and similar symptoms to those from those that actually have those problems because of an underlying food allergy. One useful historical point is the family background: is there already a clear history of atopy in the family? Does mum or dad have hayfever, asthma, eczema, because if they do and 2

3 there are atopic genes around, it makes it more likely that the infant has got an allergic problem? Another useful point will be whether the child already has signs of allergy, so does the child who s coming to you with a suspected delayed allergy to milk, causing eczema or reflux, already have a known egg allergy because they ve reacted as soon as they had it? That would make it more likely that there s allergy there. There are a number of other features though that should also give you big clues; for example, the presence of symptoms in more than one system, so the child with difficult eczema who also has gastrointestinal symptoms of reflux, colic or diarrhoea, or the child that comes to you with difficult gastrointestinal symptoms who happens to have eczema as well. That can be an important clue that there s a unifying diagnosis that both the gastrointestinal and the skin problems actually have the same single source. Another important clue would be failure to respond to treatment, so reflux that doesn t respond to first-line measures or eczema that doesn t respond to topical steroids and regular moisturisers. It s in infants like that that you need to think very carefully about possible food allergy. Another important clue would be what happens when you change the amount of potential allergen that they re consuming? When a child is moved from being breastfed to being bottle fed, there s a big increase in the amount of cow s milk protein in their diet. Do the symptoms get worse during that period, because that will be a big clue that milk could be the underlying cause? When you assess a child who you suspect has got a food allergy, you need to think carefully about what mechanism of 3

4 food allergy you re thinking about. If you suspect an IgEmediated food allergy because of rapid onset of symptoms like urticaria or angioedema, then in order to make a diagnosis you need to do the appropriate IgE-type test. That would either be a skin prick test or, more likely in primary care, a specific IgE blood test, which used to be known as a RAST test. If you have a good clinical history for immediate-type allergy, together with a positive allergy test, then you ve got a diagnosis. With non-ige-mediated allergies, if you suspect these then unfortunately the skin tests or blood tests are not useful, because they will only detect IgE-mediated-type reactivity. If you suspect a delayed allergy, you need to do an exclusion of the food that you suspect is a problem so, most commonly that would be milk during infancy and see whether the child s symptoms improve. Then after a period of four to six weeks, reintroduce the milk back into the diet to see if the symptoms return. If you notice that the symptoms improved off milk and worsened again when you went back onto milk, then you ve got a diagnosis. In order to treat allergy, the most important thing of course is allergen avoidance. In the case of food allergy, this very much falls onto the expertise of specialist allergy dieticians. Allergy dieticians will ensure that the food is avoided but also that the parents are educated in label reading. They can also ensure that the infant, who is particularly at risk of nutritional deficiency, especially in the case of milk allergy, has been given adequate advice to ensure that they get a proper nutritional diet, with all the calcium, and iron, and all the other minerals that they need. Treatment also requires that patients are able to recognise and treat reactions appropriately. In the case of IgE-mediated 4

5 allergy, that means that they either need to carry antihistamines around or in some cases, when we believe the child is at particular risk of severe reactions, they should also be carrying adrenaline auto-injectors. The sort of children that should carry adrenaline auto-injectors are those who have got a history of asthma, as well as food allergy, or have had an anaphylaxis in the past. Other factors should also come into your decisions. For example, if the child is quite remote from medical help or they re particularly anxious about the possibility of severe reactions, they may also benefit from carrying adrenaline. It s essential though that they get trained in how and when to use it and that they have a written treatment plan so they know how to treat reactions. With delayed allergies, there s less risk of severe reactions, so the focus needs to be on allergen avoidance. In both cases, either immediate or delayed-type allergy, follow-up is essential, because many children outgrow their food allergies. Repeat testing, as well as careful examination for allergic comorbidities so, for example, the development of asthma, or rhinitis, or eczema is also essential over time. To sum up, remember that food allergy is common, but it s not always obvious. Don t just think about allergy when somebody has urticaria or angioedema; remember that infants with severe eczema or gastrointestinal symptoms might also have a food allergy but that it s a delayed type. Don t try and make a diagnosis using IgE-type tests such a skin tests or blood tests; you need to consider an exclusion diet, followed by reintroduction. Remember that having a diagnosis of a food allergy has an enormous impact on the quality of life of a family and it needs 5

6 careful follow-up and adequate support, particularly from dieticians, as well as in some cases specialist follow-up. END AUDIO 6