Skin reactions and itch sensation induced by epicutaneous histamine application in atopic dermatitis and controls

Itch sensations and skin reactions induced by histamine iontophoresis at six different current intensities were studied in 27 atopic dermatitis (AD) patients and 20 healthy controls. Subjective itch ratings were assessed on a visual analogue scale (VAS) for 8-min periods after 10-sec histamine application, while changes of skin blood flow were simultaneously measured using two Laser Doppler flowmeters. Ten minutes after each histamine application, the areas of wheal and flare reactions were planimetrically evaluated. When no or weak current was applied, AD patients revealed stronger wheal and flare reactions than controls, possibly due to disturbed skin barrier function. Higher histamine doses, however, produced weaker subjective and vascular reactions in AD patients. In contrast to the controls, AD patients were unable to distinguish between weak and strong histamine stimulation, as shown by their VAS ratings. These results imply that AD patients have an altered histamine response. In particular, their afferent cutaneous nerve fibers show a decreased ability to signal itching to the central nervous system and to release vasoactive neuropeptides upon histamine stimulation.