Acute Urticaria Differential Diagnoses

Updated: Sep 13, 2016
  • Author: Henry K Wong, MD, PhD; Chief Editor: Michael A Kaliner, MD  more...
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DDx

Diagnostic Considerations

In 50% of patients with acute urticaria, a specific etiology can be identified. Brief episodes of urticaria can be associated temporally with identifiable causes, and the method of exposure (ie, direct contact, oral or IV routes) is usually known.

Urticaria may be confused with a variety of other dermatologic diseases that are similar in appearance and are pruritic, including atopic dermatitis (eczema), maculopapular drug eruptions, contact dermatitis, insect bites, erythema multiforme, pityriasis rosea, and others. Usually, however, the experienced clinician is able to distinguish these conditions from urticaria because of the lesions' distinctive appearance, the fact that they are intensely pruritic, and because the lesions blanch completely with pressure (see Clinical Presentation). [1]

In chronic urticaria, which persists for longer than 6 weeks, a cause is difficult to identify, despite perhaps even exhaustive efforts. This is known as chronic idiopathic urticaria, [2] although most of these cases are chronic autoimmune urticaria, as defined by a positive RAST result. [9, 38]

Differential Diagnoses