00:01
In this lecture, we'll discuss allergic reactions
including anaphylaxis, urticaria,
angioedema and food allergy.
00:09
So there are generally 4 types
of hypersensitivity reactions.
00:14
This is your basic science material.
00:16
Type 1 is IgE mediated
and an example would be anaphylaxis.
00:21
Type 2 is IgG or IgM mediated antigen on a target cell
and an example of that would be rheumatic heart disease.
00:30
Type 3 is when there are
circulating antigen/antibody complexes.
00:35
An example of this type of reaction
is for example serum sickness.
00:39
And a type 4 hypersensitive reaction
is generally a T-cell mediated response
such as poison ivy, or a PPD test,
or milk protein allergy
presenting as blood in the stool as an infant.
00:53
So, let's start with type 1 hypersensitivity reactions.
00:59
In general, these require exposure to a protein
that's large enough to be an antigen.
01:05
So, the patient has an initial exposure to that antigen,
and they produce an antigen-specific IgE.
01:12
That IgE now binds to a mast cell,
and on a subsequent exposure to that antigen,
they generally have a generalized mass cell degranulation
resulting in a type 1 hypersensitivity reaction.
01:28
There are many things that can trigger such a reaction.
01:31
These include foods, especially food additives,
legumes, tree nuts, seafood, eggs, dairy, shellfish, berries.
01:39
These are all very common.
01:41
In fact, among children who have
type 1 hypersensitivity reactions to food
about 85% of them are to food
when we know what the allergen is.
01:53
Still, remember, at least a third of the time
we have no idea what triggers the allergy.
01:58
Also, patients can be allergic to medications.
02:01
Probably penicillins and sulfas are the most common,
but they could also be allergic to salicylates
to certain vaccines or to anaesthetics.
02:10
Also patients can have environmental allergies.
02:14
Bee stings and wasp stings are particularly problematic.
02:18
Patients may be allergic to temperature changes
to exercise, to latex.
02:22
Lots of different possibilities.
02:25
So, urticaria is our classic type 1 hypersensitivity reaction.
02:30
We also call it "hives".
02:32
These lesions will be anywhere from 1 mm to 10 cm large.
02:37
They can be huge or small.
02:38
These lesions are profoundly itchy,
and they're stimulated by skin contact,
which means the more you scratch them,
the more they itch.
02:48
What you'll notice about them is that they sort of "come and go"
even before your eyes.
02:53
You may walk in, see a patient with hives,
and before you're done with your conversation,
the one you were looking at on the leg is gone,
and there's a new one on the arm.
03:02
They may be associated with angioedema,
which is another type of type 1 hypersensitivity reaction.
03:10
What's key is that these are acute and generally short-lived.
03:14
Patients usually only have this reaction
for maybe days to maybe a week out,
from when they're first encountered that antigen,
and had a response to it,
which would be the second time they ecountered the antigen.
03:26
Alternatively, occasionally they can become chronic.
03:30
These are when hives last longer than 6 weeks.
03:33
This can really be problematic when it happens.
03:37
So, the diagnosis of urticaria is based on appearance.
03:41
This is a great picture.
03:42
Just remember they're sort of serpiginous,
round with central clearing.
03:46
This is a classic hives reaction.
03:48
They're a little bit raised.
03:50
We're going to treat this with oral antihistamines.
03:54
That's our mainstay of therapy,
basically diphenhydramine.
03:58
Patients may add H2 antagonists, such as ranitidine, to the mix
to try and limit the effect of the histamines.
04:08
This has a minimal benefit,
but it's certainly isn't particularly harmful
to be on ranitidine for a few days
while you're waiting for your hives to improve.
04:16
What's key is steroids are generally not helpful,
so we do not routinely provide steroids
to patients with urticaria.
04:23
So, angioedema, I mentioned this earlier.
04:28
This is sort of like hives gone wild.
04:30
This is a general localized swelling
that happens in an area, often on the face.
04:37
It can happen around the eyes.
04:38
It can happen on the lips, the mouth, or the tongue.
04:42
It may happen on the genitalia,
or the extremeties,
or even in the bowel wall
causing either bowel discomfort
or nausea, vomiting, or more systemic symptoms.
04:54
What's key though and where we would worry,
is when this involves the lips, the mouth, and the tongue,
because we worry about the patency of the airway.
05:02
Sometimes, the swelling can get so bad,
the patient may have trouble breathing.
05:06
This is an allergic reaction --
or it can be inherited.
05:12
There are rare diseases such hereditary angioedema
where patients can get this randomly throughout their lives.
05:20
In specific, we sometimes see this to certain medications
and the classic one is the ACE inhibitor.
05:27
Any patient on an ACE inhibitor, who gets this reaction,
it's an emergency because we may lose that airway.
05:34
Additionally, NSAIDS can do this
and calcium channel blockers can rarely do this.
05:40
The classic one is ACE inhibitors.
05:43
So, what do we if we have a patient with angioedema?
Well, first, remove the offending agent.
05:49
Get them off the drug that's caused it
or whatever has caused it,
get them out of it, get it out of them.
05:53
Then we're going to treat it similarly to hives.
05:56
So, we're going to give the benadryl we talked about.
05:59
We'll probably do that around the clock.
06:01
We may add Zantac.
06:03
If the airway is involved,
we generally would admit these patients to the hospital
to make sure that that airway isn't goint to become compromised.
06:11
If the airway is obstructed,
we immediately give epinephrine
and provide immediate airway stabilization
and airway support.
06:19
It may require intubation
and in very rare cases, an actual tracheostomy,
if you're incapable of getting an intubation.
06:27
Sometimes a layringoscopic intubation is needed.