Understanding food allergy in young children
28
August

By Adem Lewis / in , , , , , , , , , , /


Toddlers can indeed have allergies. And there
are obviously many allergic conditions such as food allergy, eczema,
asthma and hay fever. But in toddlers the commonest allergy
we’d see is that of eczema. So, these young infants would present with
a history of eczema or recent onset eczema that is itchy, sometimes oozy and crusting,
often around the head and neck which then migrates into the flexors,
into the neck region, into the elbows and behind the knees. And where we find eczema particularly
early onset eczema that is severe, we frequently will find food allergy. So there’s a very close association
between food allergy and eczema. With the food allergy exacerbating
the eczema and paradoxically, often the eczema causing the food allergy. So, in these young toddlers we really want to
treat the skin as aggressively as we can to seal up the skin barrier and to try
as best we can to prevent the allergic march. The allergic march describes
a sequence of allergies from eczema to food allergy. And in some patients eczema and
hay fever as they get older. So food allergies are typically diagnosed
by taking a very detailed history. Either the child or the older patient would have
eaten the food and tolerated it. And obviously they are then tolerant. Or they would have developed symptoms.
Obvious symptoms of allergy would make a diagnosis. For example, if you
ate some peanut and you develop immediate onset swelling, hives, vomiting, cough and
wheezing, you’re peanut allergic. And if that’s happened on two or three occasions,
that diagnosis is even more secure. So, you need a detailed history taken by a clinician
who’s experienced in the field of food allergy. Thereafter, the testing would consist of either a skin
prick test; which is placing a drop of the allergen on the arm and lightly touching through
with a lancet and if this develops a big hive, again, that is highly suggestive — regardless
of the history unless there is a history of tolerance, but that is highly suggestive of allergy. So, where you find a large test, the patient hasn’t eaten a food or that had mild or obvious symptoms, they are then food allergic. There are of course blood tests that also detect
the same antibody: the IgE, the immunoglobulin E antibody. And these tests perform in the
same way. The higher the test, the more accurate. And of course, if the test is negative, then
it’s highly predictive of not having that allergy. The final way and the gold standard
are to actually eat the food. So, if you can eat a handful of peanuts and you tolerate
that with no symptoms, regardless of any test result, result, you are tolerant of peanut. To make a diagnosis of food allergy
we rely on the clinical history and testing. The testing modalities include a skin prick test
where a drop of the allergen is placed on the arm and a Lancet is used to lightly touch through this
and to look for a hive that may result. And then a blood test can also be performed and this measures the IgE antibody: the allergy antibody. So starting with a clinical history,
sometimes this is very obvious. For example, if you’ve eaten a single peanut
and developed significant symptoms, you’re very likely
to be peanut allergic. If your symptoms were equivocal
or the peanut has not been eaten and there are other risk factors,
we would then perform testing. The skin prick test like the blood test is
highly accurate when the test results are high. And of course,
when they are negative. So, the negative predictive value, the chance that you will not react to the food if your test is negative is extremely high. The positive predictive value, in other
words, the chance that you do have the allergy if the test result is high on skin prick test
or IgE, again, is also high. Where a diagnosis is uncertain, we then rely on an
oral supervised food challenge test. So here we would provide increments of the food
in a safe and supervised setting and look for symptoms. And of course, if an age appropriate amount of the food
is eaten with no symptoms that child is peanut tolerant. You must be cautious of either high
speed tests such as IgG4 tests. These are not accurate tests for food allergy. So of course, there are many allergic conditions. For a condition such as eczema, we have very
effective creams and ointments which can at least control the disease whilst we await
the resolution of the disease. For asthma, again, we have medications
that provide very effective control. And for hay fever, we have immunotherapy. So, if the patient has significant hay fever,
we’re able to treat this or at least moderate the disease through using immunotherapy and other medicines
as well to help control these seasonal symptoms. For food allergy, this is more complex.
Some food allergies are outgrown. So, for example, milk and eggs
are considered childhood allergies as very few children will carry this
into the second and third decades of life. For peanut allergy and sesame and tree-nut allergy,
this is different. And families often ask about
active programmes to treat this. So, we are currently researching
this and there are various modalities. Patches applied to the skin and small measured oral
increments of these in a safe and supervised setting. But these currently remain in the research setting
and should not be applied at home. These are not home remedies, as remember
you’ll be feeding the allergen to an allergic patient and that can induce severe reactions. So in considering food allergies, we now know that many food allergies are outgrown, such as egg and milk. So indeed, young infants with egg and milk allergy
enjoy a very good prognosis, typically after three or four or five years,
they’ll start safety ingesting baked milk products, because the heating damages the allergen, and in a year or two later after that they’ll tolerate
just regular milk and egg based products. Wheat is commonly outgrown
as are soy and some other allergies. Of course, in about ten to fifteen percent
of these patients they will not outgrow their allergy and that can be very troublesome over a lifespan. Certain allergies are generally not outgrown;
only outgrown in ten to fifteen percent of children. And this would include fish allergy,
shellfish allergy, peanut allergy, tree nut allergies such as cashew and pistachio and walnut allergy, and of course sesame allergy. These are not
outgrown in most children.


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