Physical urticaria

The different types of physical urticaria are triggered by mechanical and t hermic stimuli or electromagnetic waves. Localized forms restricted to the skin and mucous membranes are mostly observed, but also generalized urticar ia with variable extracutaneous manifestation can be elicited. Usually, phy sical urticaria occurs sporadically, only rarely in a familial form, either as an isolated disease or in association with chronic urticaria. Similar s timuli may evoke a different clinical pattern of symptoms in different pati ents. Often, a short interval between physical stimulus and reaction points to a causal relationship, but in delayed types of physical urticaria the e xact diagnosis may be missed without provocation tests. The clinical implic ation of physical urticaria is demonstrated by investigations showing a sig nificant degree of disability in affected patients compared to other types of urticaria. In addition, symptomatic relief by antihistamines is often un satisfactory. Thus, alternative therapeutic strategies including the induct ion of tolerance, e.g. in solar urticaria, are mandatory. These problems ar e caused by a still incomplete understanding of the crucial pathophysiologi cal aspects: most likely inflammatory reactions involving leukocytes, endot helial cells and nerves stimulated by various mediators play an important r ole in this group of urticaria.