Question:
I would be interested in the differences in immune mechanisms responsible
for reactions described by these two words. Could you please expand?
Answer:
One textbook defines anaphylaxis as "a severe, abrupt, untoward
immunologic event manifested by cutaneous (urticaria/angioedema),
respiratory (bronchospasm, laryngeal edema), cardiovascular (hypotension,
arrhythmias, myocardial ischemia), and gastrointestinal (nausea, vomiting,
pain, diarrhea) signs and symptoms occurring singly or in combination."
Most such reactions are IgE-mediated, though there are other immunologic
routes through which they may occur. This broad definition subsumes
reactions that have been called anaphylactoid, and makes that term
meaningless.
Clinically there is reason to try to distinguish anaphylactic reactions
from "severe allergic reactions," though there is no understandable
definition that could help us do so. Contact with a cat might lead to
urticaria and bronchospasm, fulfilling the above criteria for the diagnosis
of anaphylaxis, but few would call it that. The diagnosis of anaphylaxis is
usually reserved for those reactions which have the potential of being
fatal: usually those which include significant hypotension, or laryngeal
edema.
The danger in too broad a use of the "A" word is that it might trivialize
that word and diagnosis, leaving us without proper warning in situations of
real potential danger to life. The danger in overly restricting its use is
that we might fail to signal the possibility of progression of reactions in
any particular individual.
The broad definition quoted above almost demands that one who describes
an anaphylactic reaction include a listing of the symptoms that constituted
that state. Otherwise there are bound to be misunderstandings, and the word
itself could lose its usefulness. This matches the definitions that I have been given in a variety of
settings, including immunology classes, though there is an important
difference -- everything I have been taught includes that it is a
'systemic reaction' [see the next paragraph]. Anaphylaxis using the
systemic reaction definition then gets broken down into mild,
moderate, severe and anaphylactic shock. Basically, anaphylaxis in those contexts was taught as being a
systemic allergic reaction, which is to say that the allergen is at
point A [e.g. for a bee sting, point A is the sting site], but the
patient is having a reaction at point B [somewhere other than the
sting site]. For example, the person who is stung by a bee on the
foot is having hives on the stomach and back and difficulty breathing
[though perhaps not severe]. By the definitions I have been exposed
to, such a reaction IS anaphylaxis, as would a reaction where the same
person just had the hives, but not the trouble breathing. Depending
how far and bad the reaction was, it would be considered mild,
moderate, or severe. And yes, technically, asthma triggered by
anything other than an inhaled allergen WOULD be an anaphylactic
reaction -- not sure if it really is appropriate or not to think of it
that way or not, but it might be for severe attacks -- I wouldn't want
to necessarily stick someone with epi just because they are having an
asthma attack and only an asthma attack, even if it is caused by a
non-inhalant, at least not an attack that is responsive to meds and
not inherently life-threatening...
To be considered **anaphylactic shock**, which IS life threatening,
under what I have been taught, the person has to have respiratory
distress AND/**OR** significant hypoperfusion.
Thus, according to what I have been taught, anaphylaxis is not always
life threatening, but it always has the potential to become life
threatening [should the reaction progress]. The problem is that one
doesn't always know at the onset of the reaction how far it will go,
nor how quickly. Which is why some epi protocols call for
administering epi at the first sign of a systemic reaction [that point
B S/Sx when the allergen is at point A] -- because waiting until the
pt is in respiratory distress or significantly hypotensive can be
waiting until it is too late.
Finally, a recent study showed that the average time it takes for a
patient to die from an anaphylactic reaction, from time of onset of
S/Sx until death, is seven minutes... Not much time in which to guess
"is the reaction going to stop at this point or is it going to keep
going"...
Finally, even in the contexts that I have been taught about
anaphylaxis, a distinction *is* made between anaphylactic reactions
and anaphylactoid reactions. The distinction is unimportant for
emergency treatment of an acute reaction, but becomes important for
future patient care. The differene is in the immune mechnism through
which the reaction takes place. The same type of reaction may be seen when there is immune-complex
activation of Complement, and this is important in making future medical
plans, but even in the case of classic IgE-mediated anaphylaxis attention
must be paid to the many possible immediate causes of the process. Does it
really help to multiply terms? This may be becoming more than most people want to follow. I am interested
in your explanation, and would be delighted to discuss further by email, if
not here.
