Localized heat urticaria: a clinical study using laser Doppler flowmetry.

We studied the pathophysiology of localized heat urticaria using laser Doppler flowmetry (LDF) in two patients with this rare disease. In heat challenge tests, performed with different challenge times and temperatures, a heat stimulator with a thermoregulated metal disc was utilized. Immediately after removal of the heat source, cutaneous blood flow (CBF) changes in the tested sites were monitored with LDF. In both patients the increase in (CBF) took place at some intervals after a heat challenge, synchronous with the start of the urticarial response. This interval, or the latency time (LT), showed distinct inverse proportion to the intensity of heat stimuli and was prolonged by effective treatments, such as application of antihistamines and repeated heat exposure by LDF. Therefore, the time of latency might be regarded as a good indicator of the severity of illness and therapeutic effectiveness, and thus might reflect the relationship between the degree of heat stimuli and the releasing process of chemical mediator(s) in patients with localized heat urticaria (LHU).