Histamine-induced itch and alloknesis (itchy skin) in atopic eczema patients and controls

Alloknesis ("itchy skin") after histamine iontophoresis was studied together with itch sensations and skin reactions in 19 atopic eczema patients and 20 controls at the forearm and at the scapular area. Compared to controls, atopic eczema patients showed significantly reduced alloknesis or total lack of it in the area around a skin site to which histamine had been iontophoretically applied, although histamine elicited itching in most patients. As previously demonstrated, patients with atopic eczema also developed significantly smaller flares. However, covariance analysis revealed that the smaller alloknesis areas in atopic patients were not statistically related to the smaller flares. Our results suggest that in atopic eczema a diminished responsiveness of primary afferent nerves to histamine is not compensated by a higher central nervous sensitivity reflected in more vivid alloknesis responses to histamine. Therefore, we conclude that histamine is probably not the key factor of the spontaneous itch experienced by patients with atopic eczema.