Delayed pressure urticaria: an investigation of some parameters of lesion induction.

Two patients with delayed pressure urticaria were studied to define some of the physical parameters related to experimental lesion induction using a pressure-testing device. Graded pressures from 48 to 234 gm/mm2 were applied for 1 to 180 seconds on several anatomic areas. Experimentally induced lesions were symptomatically, clinically, and histologically identical to spontaneous wheals and reached a maximum size 9 hours after the stimulus. The threshold response found was related to the amount of pressure, the duration it was applied, and the anatomic area tested. Sites that previously reacted to pressure were refractory to additional stimuli for at least 24 to 48 hours. The mediator for delayed pressure urticaria remains unknown, and some patients do not respond to oral corticosteroids.