The patient is generally very uncomfortable, with intense
itching. There may be a history of similar episodes and
perhaps a known precipitating agent (bee sting, food, or
drug). Most commonly the patient will only have a rash.
Sometimes this is accompanied by edematous swelling of the
lips, face and/or hands (angioedema). In the more severe
cases, patients may have wheezing, laryngeal edema and/or
frank cardiovascular collapse (anaphylaxis).
The urticarial rash consists of sharply defined, slightly
raised wheals surrounded by erythema and tending to be
circular or serpiginous. Each eruption is transient, lasting
no more than 8-12 hours, but it may be replaced by new
lesions in different locations.
What to do:
Attempt to elicit a precipitating cause, including drugs,
foods, stress, or an underlying infection or illness,
(e.g., collagen vascular disease, malignancy, or, when
accompanied by arthralgias, anicteric hepatitis).
For immediate relief of severe pruritis, you can try 0.3cc
of epinephrine (1:1000) subcutaneously, but this wears off
quickly, and adds a number of side effects the patient may
find worse than the itching: tachycardia, shaking, dry
mouth, wet palms, hypertension, and even angina and
myocardial infarction.
For continued relief administer diphenhydramine (Benadryl)
or hydroxyzine (Vistaril) 50mg po.
For prolonged relief from itching prescribe
diphenhydramine (Benadryl), hydroxyzine (Atarax) 25-50mg,
cyproheptadine hydrochloride (Periactin) 4mg qid or
terfenadine (Seldane) 60mg bidfor the next 48 hours.
To reduce the rash, prescribe cimetidine (Tagamet) 300mg
q6h. Other H2 blockers, such as ranitidine (Zantac) and nizatidine (Axid) also appear to work in similar doses.
To blunt the entire allergic process, give prednisone 60mg
po now and prescribe 20mg qd for 2 days.
Inform the patient that the cause of hives cannot be
determined in the vast majority of cases. Let him know
that the condition is usually of minor consequence but can
at times become chronic, and, under unusual circumstances,
is associated with other illnesses. Therefore, the patient
should be provided with elective followup care.
What not to do:
Do not havethe patient take aspirin. Some patients
experience a worsening of their symptoms with the use of
aspirin. Morphine, codeine, reserpine, and alcohol, as
well as certain food additives such as tartrazine dye, are
often allergens or potentiate allergic reactions, and
benzoates should probably also be avoided.
Discussion
Although the treatment of anaphylactic shock is beyond the
scope of this book, when hypotension is present, aggressive
intravenous fluid therapy should be instituted, along with
the intravenous administration of the medications above.
Simple urticaria affects approximately 20% of the
population at some time. This local reaction is due at least
in part to the release of histamines and other vasoactive
peptides from mast cells following an IgE mediated antigen-
antibody reaction. This results in vasodilatation and
increased vascular permeability, with the leaking of protein
and fluid into extravascular spaces. The heavier concentration of mast cells within the lips, face, and hands explains why these areas are more commonly
affected. In asthma, the bronchial tree is more affected,
whereas with eczema, the skin in knee and elbow creases is
most heavily invested with mast cells and the first to
develop hives.
References:
Rusli M: Cimetidine treatment of recalcitrant acute allergic urticaria. Ann Emerg Med 1986;15:1363-1365.
