Urticarial lesions: If not urticaria, what else? The differential diagnosis of urticaria:

Acute urticaria is self-limiting, and a cause can be identified in many patients. Chronic urticaria is a long lasting disease, and patients are commonly examined for an autoimmune origin and for associated diseases. Although the diagnosis of urticaria is straightforward in most patients, it may pose some difficulties at times and it may require a careful differential diagnosis with a number of conditions. Urticarial syndromes comprise both cutaneous and systemic disorders. Part I of this two-part series focuses on the clinical and histologic features that characterize common urticaria and on the cutaneous diseases that may manifest with urticarial lesions and must be considered in the differential diagnosis.

Learning objectives

After completing the learning activity, participants should be able to distinguish between the typical wheals of urticaria and urticarial lesions suggesting other diagnoses and to assess patients with urticarial lesions in order to exclude or confirm other cutaneous diseases.

Key words: bullous pemphigoid, drug eruption, insect bite reactions, urticaria, urticarial dermatitis, urticaria pigmentosa

Abbreviations used: FcεRIα, high affinity IgE-receptor, IGD, interstitial granulomatous dermatitis, NEH, neutrophilic eccrine hidradenitis, NSAID, nonsteroidal antiinflammatory drug, PUPPP, pruritic urticarial papules and plaques of pregnancy