Neuronal sensitization for itch in patients with chronic pruritus

Abstract

Itch is one of the major symptoms of various skin diseases. Although specific neuronal pathways for itch were identified both peripherally and centrally, they still fail to explain itchy skin observed in patients with chronic pruritus. In this study, sensitivity to itchy and painful stimuli in patients with atopic dermatitis was investigated. Histamine‐prick evoked enormous itch in their lesional skin, while less itch in their non‐lesional skin than healthy subjects. Flare reaction was not significantly different between their non‐lesional and lesional skin, rather smaller than healthy subjects. Mechanical (pin‐pricks), electrical, heat and chemical (injection of pH3 solution) stimuli evoked intense itch in their lesional skin and partly also in their non‐lesional skin, while only pain in healthy subjects. Itch was also, but not intensely, evoked in healthy subjects by injection of pH3 solution after sufficient histamine stimuli. These results confirm the presence of itchy skin with hyperkinesis (excessive itch by itchy stimuli) and allokinesis (itch by non‐itchy stimuli) in patients with atopic dermatitis, which is so intense that painful stimuli cannot suppress but evoke itch, and suggest that neuronal sensitization is involved in their itch not only peripherally but also centrally.