Cholinergic Urticaria

Clinical Signs and Symptoms

The classic appearance is that of numerous punctuate wheals (13 millimeters) surrounded by a large erythematous flare (“fried-egg” appearance). As the response progresses, the flares may coalesce to form large areas of erythema. The wheals typically begin on the trunk and neck and spread distally to involve the face and extremities. Patients will often have sensations that can include itching, burning, or tingling. Rarely, this can progress to systemic symptoms such as hypotension, angioedema, and bronchospasm.

Testing

The presence of classic lesions in the setting of a typical trigger is enough to suggest a diagnosis, but diagnostic testing can be done for confirmation. A provocation test can be performed, which involves an intradermal injection of methacholine. A positive test produces hives around the injection site. This test, however, is only positive in about 33% of patients. Another type of provocation test is to have the patient mimic the activity that caused the hives (e.g., exercising, eating a certain food) in an attempt to produce a reaction. Last, the examiner can try to raise the patient's core body temperature by having the patient partially submerged in a hot water bath at 40 C. The appearance of urticaria confirms the diagnosis.

Nonpharmacologic

Identification and avoidance of known triggers is the first step in controlling cholinergic urticaria. Avoiding strenuous exercise in hot weather and bathing in hot water may also reduce the chance of having a reaction. Athletes may be forced to change their training behavior and do more activities indoors in a temperature-controlled environment, and in extreme cases, an athlete may be forced to change his or her sport to avoid having an outbreak of urticaria.

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