Transcutaneous Slowly Depolarizing Currents Elicit Pruritus in Patients with Atopic Dermatitis
Roman Rukwied, Mark Schnakenberg, Hans Jürgen Solinkski, Martin Schmelz, Elke Weisshaar
Slowly depolarizing currents applied for one minute have been shown to activate C-nociceptors and provoke increasing pain in patients with neuropathy. This study examined the effect of transcutaneous slowly depolarizing currents on pruritus in patients with atopic dermatitis. C-nociceptor-specific electrical stimulation was applied to areas of eczema-affected and non-affected skin in 26 patients with atopic dermatitis. Single half-sine wave pulses (500 ms, 0.2–1 mA) induced itch in 9 patients in eczema-affected areas of the skin (numerical rating scale 5 ± 1), but pain in control skin (numerical rating scale 6 ± 1).Sinusoidal stimuli (4 Hz, 10 pulses, 0.025–0.4 mA) evoked itch in only 3 patients in eczema-affected areas of the skin but on delivering pulses for one minute (0.05–0.2 mA) 48% of the patients (n= 12) reported itch with numerical rating scale 4 ± 1 in areas of eczema-affected skin. The number of patients reporting itch in eczema-affected areas of the skin increased with longer stimulation (p < 0.005). These results demonstrate a reduced adaptation of peripheral C-fibres conveying itch in patients with atopic dermatitis. Sensitized spinal itch processing had been suggested before in atopic dermatitis patients, and this could be present also in our patients who therefore might benefit from centrally acting antipruritic therapy.
This study showed that electrical stimulation, which is known specifically to activate unmyelinated nociceptors, evoked itch in approximately 50% of 26 patients with atopic dermatitis when one minute slowly depolarizing pulses were delivered transcutaneously to eczema affected skin.The number of patients perceiving itch increased with longer stimulation (p< 0.005) and adaptation of peripheral C-nociceptors was less pronounced. Sensitized itch-conveying C-fibres and facilitated central processing may explain the persistence of itch in patients with atopic dermatitis. Patients identified by the electrical stimulation protocol, used in this study, as having sensitized spinal processing for itch, might benefit from centrally acting antipruritic therapy.