11.15 Urticaria (Hives)

agk’s Library of Common Simple Emergencies

Presentation

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 have the 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.

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