Managing urticaria in primary care.
Urticaria is characterised by transient wheals that consist of a swollen palpable centre often surrounded by an erythematous flare, associated with itching or, less commonly, a burning sensation. Individual wheals usually disappear within 1 to 24 hours leaving normal skin. Wheals may be accompanied by angioedema, a more deep-seated flesh-coloured or erythematous swelling of skin or mucous membrane, which may last longer than 24 hours. Urticaria is classified as acute when it resolves within six weeks and chronic when its duration exceeds six weeks. Chronic urticaria is now sub-classified into chronic spontaneous urticaria (CSU) and chronic inducible urticaria. The prognosis for eventual recovery from spontaneous and inducible urticaria is excellent. However, the time course is unpredictable and may extend to years, often following a relapsing and remitting course. Urticaria results from the release of inflammatory mediators from dermal mast cells, resulting in vasodilatation, plasma extravasation, recruitment of immunologically active cells and sensory nerve stimulation. The cause of urticaria cannot usually be precisely identified for most affected individuals. IgE-mediated food allergy is rarely the cause of CSU in patients with the daily appearance of urticarial lesions, although it should be considered in CSU patients with intermittent symptoms. For patients with CSU a differential full blood count and inflammatory markers are all that are routinely recommended. It is also reasonable to test thyroid function and check for circulating thyroid autoantibodies as there is an association between CSU and thyroid autoimmunity.