The evaluation of a patient with urticaria and angioedema

Urticaria is defined by the development of wheals and/or angioedema and is primarily mast cell driven. Urticarial lesions are evanescent pruritic plaques, with each discrete lesion lasting <24hours and leaving normal skin after resolution. Urticaria is defined by its duration, with acute urticaria lasting ≤6 weeks and chronic urticaria lasing >6 weeks. Acute urticaria in the absence of anaphylaxis does not necessitate a workup, but the patient history may guide the need for allergy testing. Chronic inducible urticaria is brought on by a specific trigger and requires provocation testing. Chronic spontaneous urticaria lacks a known trigger and warrants basic screening laboratory tests to rule out underlying systemic disease. Urticaria associated with systemic symptoms, discrete urticarial lesions lasting >24hours, and/or lesions that leave residual ecchymosis warrant further workup for underlying causes.

Angioedema in the absence of wheals is primarily bradykinin mediated, and is classified as hereditary if there is a family history, or acquired in the absence of one. The most common subtype of acquired angioedema is angiotensin converting enzyme inhibitor (ACE-I) associated angioedema, which is diagnosed on history. There are multiple subtypes of hereditary angioedema (HAE), classified by their biochemical or genetic cause. HAE occurs in specific episodes usually lasing 36–72hours, and may have a known trigger. HAE most commonly affects the skin, gastrointestinal tract, and upper respiratory tract. In the absence of a history of ACE-I use, screening C4 level and testing for C1 inhibitor levels and function as well as C1q can help differentiate among the other acquired and HAE subtypes.

There exist multiple validated scoring systems for evaluating disease severity and response to therapy in urticaria and angioedema during initial and subsequent patient visits.