Delayed pressure urticaria.

Delayed pressure urticaria is a physical urticaria where erythematous, often painful swellings occur at sites of sustained pressure on the skin, after a delay of several hours. If sought, it is present in up to 40% of patients with ordinary chronic "idiopathic urticaria" to a varying degree. Compared with other urticarias, the pressure-induced lesions impair the quality of life of patients most severely. The pathogenesis is not well characterized, but whealing is dependent on mast cell activation, with the histology of lesions also showing a deep dermal inflammatory infiltrate of neutrophils and eosinophils, without vasculitis. Treatment of delayed pressure is generally unsatisfactory, and is often resistant to antihistamine and a range of anti-inflammatory medication. Oral steroids, although the most effective therapy, are unsuitable for long-term use. Delayed pressure urticaria may persist for many years, and improved or novel methods of management are under investigation.