Urticaria

Urticaria describes a group of conditions in which itchy weals and red patches occur in the skin. They affect both children and adults. The weals are caused by the release of histamine or other chemicals from mast cells. These in turn increase the permeability of small blood vessels which leak into the skin causing localised swelling (Figure 13.6). Urticaria can be short lived or long term and appear in small patches or large areas, map-like, across the body. In some instances, urticaria is accompanied by angioedema in which there is deeper swelling often of hands, eyelids or lips, but can occur anywhere.

Figure 13.6 Urticaria.

There are many different classifications of urticaria. Table 13.5 is taken from guidelines from the British Association of Dermatologists (Grattan and Humphreys, 2007).

Table 13.5 Different types of urticaria.   Overall clinical description of urticaria   Subtypes   Ordinary   Acute (up to 6 weeks continuous activity) Chronic (6 weeks or more of continuous activity) Episodic (acute, intermittent or recurrent activity)   Physical (reproducibly induced by the same stimulus)   Mechanical (e.g. delayed pressure, symptomatic dermographism, vibratory angioedema) Thermal (e.g. cholinergic, cold contact, localised heat) Others (e.g. aquagenic, solar, exercise induced)   Angiodema without weals   Idiopathic Drug induced (e.g. ACE inhibitors) C1 esterase-inhibitor deficiency   Contact urticaria (with allergens or chemicals)       Urticarial vasculitis (as defined by a skin biopsy)       Autoinflammatory syndromes   Hereditary (e.g. cryopyrinassociated periodic syndromes) Acquired (e.g. Schnitzler syndrome)