Local heat urticaria/angioedema: evidence for histamine release without complement activation.

A 42-yr-old white woman reported onset in 1976 of local pruritus, burning, erythema, and edema within minutes after exposure in heat. With more extensive exposure, she occasionally had transient headaches and nausea. In order to investigate the etiology of this condition, her forearm was exposed to water at 44 degree C for 4 min. Within a few minutes, a lesion identical to her spontaneously induced ones developed only at the area exposed to heat. Samples of venous blood from this extremity demonstrated a transient rise in plasma histamine levels without any significant change in serum hemolytic complement activity or in C3, C4, or factor B. These findings suggest that this rare syndrome involves local activation of mediator release from mast cells, without participation of the complement system.