1. ^*Division of Environmental Dermatology and Allergy GSF/TUM, Technical University Munich, Germany
2. ^†Department of Dermatology and Allergy Biederstein, Technical University Munich, Germany
3. ^‡Department of Nuclear Medicine, Technical University Munich, Germany
4. ^§Department of Neurology, Technical University Munich, Germany

Correspondence: PD Dr Ulf Darsow, Klinik und Poliklinik für Dermatologie und Allergologie am Biederstein, Technische Universität München, Biedersteiner Str. 29, 80802 München, Germany. Email: ulf.darsow@lrz.tum.de

Received 17 July 2000; Revised 21 September 2000; Accepted 26 September 2000.

Abstract

The subjective sensation of itch is a complex emotional experience depending on a variety of factors. In this study, the central nervous processing of pruritus was investigated in a human model. Activation of involved cerebral areas was correlated to scales of nociception and skin reactions. Six healthy male right-handed subjects participated in a standardized epidermal stimulus model with nine increasing doses of histamine dihydrochloride (0.03%-8%) on their right forearms. Controls consisted of three NaCl stimuli. Cerebral activation patterns were determined by H₂ ¹⁵ O positron emission tomography 120 s after stimulation. Dermal reactions to the stimulus (wheal, flare, temperature) were coregistered during the procedure. Itch sensation was determined by visual analog scale rating. Pain was not reported during the study; all volunteers had localized itch from 0.03% histamine on. Subtraction analysis versus control revealed significant activation of the left primary sensory cortex and motor-associated areas (mainly primary motor cortex, supplementary motor area, premotor cortex). Predominantly left-sided activations of frontal, orbitofrontal, and superior temporal cortex and anterior cingulate were also observed. Correlation analysis revealed coactivation of dermal reactions and cerebral response to itch in the following Brodmann areas with a Z score greater than 5: wheal, areas 5 (bilateral) and 19 (right); flare, areas 2–5 (left); temperature, area 10 (left) and left insula. Itch intensity ratings were mainly correlated with activation of the left sensory and motor areas. Functional covariates of the itch sensation in the central nervous system were identified. The intention to pruritofensive movements is probably mirrored by the activation of motor areas in the cortex. Other areas may be involved in emotional processing of sensations. Skin reactions wheal and flare also had significantly activated covariate areas in the central nervous system.