Heat urticaria: a revision of published cases with an update on classification and management.

Heat urticaria (HU) is a rare type of physical inducible urticaria, characterized by itchy erythema and well-demarcated weals appearing soon after heat exposure. Most cases occur in female patients aged 20-45 years. Both localized and generalized forms exist, depending on the limitation of the reaction to the skin area directly exposed to the physical stimulus or the involvement of distant sites, respectively. In most cases, HU is an immediate reaction, but delayed forms (mostly familial) have been described. HU is a long-lasting disease with overall duration at diagnosis of approximately 2 years. In about half of cases it is associated with systemic symptoms such as weakness, wheezing, headache, flushing, nausea, vomiting, diarrhoea, tachycardia, even dyspnoea or syncope. The main differential diagnosis includes cholinergic urticaria, exercise-induced anaphylaxis and solar urticaria. The diagnosis of HU is established by provocation testing, which is also helpful to evaluate the critical temperature threshold. The mean threshold temperature is about 44 °C. A heat desensitization programme can be an effective treatment. Nonsedating H1 antihistamines administered at licensed doses are the mainstay of symptomatic therapy in nearly 60% of patients, but full symptom relief is achieved in only a minority of them. Omalizumab has proven effective in recent case reports.