So, the last type of type 1 hypersensitivity reaction
we'll talk about is anaphylaxis.
This is the absolute worst of all of them.
This is a system-wide type 1 hypersensitivity reaction.
It has symptoms in multiple systems.
So in dermatologic system,
they will have hives, or itching, or angioedema.
But they will also have respiratory symptoms,
including shortness of breath,
wheezing, and throat swelling.
And then they may have cardiac symptoms,
including tachycardia or hypotension.
It may be a distributive shock type picture.
So, if we see patients with a type 1 hypersensitivity reaction
and especially with anaphylaxis or bad angioedema,
we worry about this phenomenon.
This is what we call the biphasic reaction.
Generally, what happens is
they're exposed to allergen time zero,
and then they have that immediate reaction.
But then that reaction gets better,
and we might be lulled into a false sense of security and say,
"Oh, patient can go home. They're doing much better."
But then generally about 12 to 24
and sometimes even farther out,
hours later they can have a second reaction.
It's like a biphasic reaction and we worry about that.
So, patients who have anaphylaxis,
even if they're feeling better,
will often get admitted to the hospital
for a period of observation.
Most people will do it for 24 hours,
although there are rare cases
of 72 hours later patients having a biphasic reaction.
So we just have to be conscious
of the potential risk for recurrence of their severe symptoms.
How do we treat anaphylaxis?
First, IM epi.
Patients who have a history of severe allergies,
essentially bee sting allergies or other things,
may have IM epi available to them on their own.
We call this the EpiPen
and this can be given to any child
who's having an anaphylactic type reaction.
Alternatively, we will also give them antihistamines
For patients with anaphylaxis,
we often do add systemic corticosteroids.
It's sort of like throwing the kitchen sink and everything.
If we're really worried about these patients,
will throw in some steroids, as well.
We may use albuterol for wheezing.
In severe cases, they require intubation and epi drip
or something like that
to really control the anaphylaxis.
So, let's switch gears now and talk about,
how do we test for a patient who's had an allergic reaction.
A patient came in,
they ate a number of different food items,
they had an anaphylaxis.
We want to figure out
what it is that's triggering this patient's allergies.
There are a few different ways we can test for allergies.
We can do RAST testing
which is a blood test
looking for antibodies directed at certain antigens.
We can do skin prick testing
where we prick in small amounts
of the derived protein for that particular food
and look for a skin reaction.
Or we can do an actual taste test,
if it's a food allergy,
where the patient actually eats the food
and we wait and see whether they have anaphylaxis.
The food test is the most specific.
We could say, 'Yes, they eat peanuts. They had a reaction.
We know the peanut is the thing.'
However, it's a little bit dangerous
because while we dilute the food in tiny, tiny amounts,
there's always a concern they could go into anaphylaxis
right there in the office while you're doing the test.
However, RAST testing is fairly safe.
It's just drawing blood and sending it to the lab
but the problem is, the false positive rate is very high.
For patients who have skin prick testing
and RAST testing to a food,
as many as 90% of them who test positive for a particular food
will not actually be allergic to that food.
So, we have to watch out
that we end up putting children on severely restricted diets
for something that they don't need to be on.
Here's a picture of a patient getting skin prick testing.
They're having the purified protein injected directly into the skin.
So things we'll typically test for, in terms of food allergies,
are milk, soy, eggs, nuts and legumes.
Remember, a peanut is not a nut.
It's a legume.
So, patients with peanut allergies may be okay to eat walnuts,
and patients with walnuts may be okay to eat peanuts.
You can't assume that all nuts are allergic at the same time.
There are also non-IgE mediated food reactions that patients can have.
The classic is celiac disease
which is an allergic reaction to gluten in the diet.
It's not IgE mediated.
It's IgA mediated but you get the idea.
Milk protein allergy in infants under 12 months
will not present with wheezing, or rash, or hives.
It often presents with blood in the stool.
This happens to about 2-3% of infants.
This is a type 4 hypersensitivity reaction
and it gets better.
After about a year of life,
these infants can usually return back to milk proteins
without any problems.
Very, very rarely that same reaction
can occur in the small bowel instead.
This is called FPIES.
Patients may have profound dehydration,
vomiting and bloody diarrhea. They can get very sick.
So, another one is eosinophilic esophagitis
and eosinophilic gastroenteritis.
This is when patients have
eosinophilic infiltration of their intestinal lining
as a result of an allergic type reaction.
This generally presents with pain.
These patients will have dysphagia,
and they may have nausea and vomiting.
It's not to a particular food,
it's just that they tend to be irritated
in terms of the lining of their intestine
or their esophagus or their stomach
and this can cause real problems.
So, how do we diagnose food allergy?
Well, for IgE mediated reactions,
we generally test just like regular allergies like we discussed,
with either a RAST or a skin prick test,
or if we really want to know,
a food challenge.
If we suspect diabetes, we're going to get TTG and IgA levels.
If we suspect infantile milk protein allergy,
really we don't do a test for it so often.
We usually just start them on a new diet without cow's milk or soy protein in it.
and then we see how they do.
And if they get better,
we've made our diagnosis.
If the child is breastfed,
we'll have mom do an avoidance diet and still breastfeed
and that usually works.
For eosinophilic esophagitis,
we really need to diagnose by doing endoscopy and biopsy.
So, that's my review of allergies and anaphylaxis in children.
Thanks for your time.