Cutaneous field stimulation (CFS): a new powerful method to combat itch

Abstract

Scratching the skin, while instantly relieving itch, often aggravates itch over time due to skin injury. To relieve itch, without damaging the skin, a new technique termed cutaneous field stimulation (CFS) was developed and tested on 21 subjects. CFS uses a flexible plate with needle-like electrodes (n = 16) to electrically stimulate nerve fibres in the superficial skin. The electrodes were stimulated consecutively (4 Hz per electrode, pulse duration 1 ms, intensity 0.4-0.8 mA, 25 min). CFS resulted in a pricking and burning sensation that usually faded rather quickly. The burning sensation was still present during a selective block of impulse conduction in myelinated fibres indicating that nociceptive C-fibres are activated by CFS. Furthermore, a flare reaction developed around the CFS electrodes indicating activation of axon reflexes in nociceptive C-fibres. Itch, elicited by transdermal iontophoresis of histamine, was abolished within the skin area pre-treated with CFS, and was reduced to 14% of control 10 cm distally. Contralateral effects were small or non-existent. After 4 h, itch was reduced ipsilaterally to 32% of control. In comparison, 2 h after transcutaneous electrical nerve stimulation (TENS; 10-20 mA, 100 Hz, 25 min) ipsilateral itch was reduced to 56% of control. In conclusion, CFS offers a powerful new method for combating itch. It is suggested that CFS acts through endogenous central inhibitory mechanisms that are normally activated by scratching the skin.

Comparison of Responses of Primate Spinothalamic Tract Neurons to Pruritic and Algogenic Stimuli

“…Experimental itch and accompanying dysesthesiae were enhanced by a local anesthetic ) and attenuated in hyperalgesic skin surrounding a capsaicin injection ). These studies demonstrated functional interactions between pruritic and nociceptive neural systems and lend support to the hypothesis that the mechanisms subserving itch are inhibited centrally by mechanisms that underlie pain and hyperalgesia Brull et al 1999;Graham et al 1951;Nilsson et al 1997;Ward et al 1996).…”

“…Another property expected of a candidate pruriceptive neuron in the CNS is that its activity is inhibited by algesic stimuli applied to normal skin and by the development of algogenic dysesthetic states such as allodynia and hyperalgesia (Bickford 1938;Brull et al 1999;Graham et al 1951;Koppert et al 1993;Nilsson et al 1997;Ward et al 1996). Rather than being inhibited by capsaicin, most of the STT neurons in the present study were vigorously excited, after which they became sensitized to stroking and to punctate stimuli.…”

Selective Stimulation of C Fibers by an Intra-Epidermal Needle Electrode in Humans

“…We noticed in previous studies that IES actually activates C fibers when a stimulus intensity higher than the threshold for A fibers is used. Similar results were reported by Nilsson et al [17] and Nilsson and Schouenborg [18] who used a needle-like electrode. However, this indicates that the stimulus inevitably activates A fibers at the intensity necessary to activate C fibers.…”

Frontiers in pruritus research: scratching the brain for more effective itch therapy

“…The inhibition of itch by painful stimuli has been experimentally demonstrated by use of various painful thermal, mechanical, and chemical stimuli (S8). Painful electrical stimulation reduced histamine-induced itch for hours in an area spanning 10 centimeters beyond the site of stimulus, suggesting a central mode of action (48). Recent results suggest that noxious heat stimuli and scratching produce a stronger itch inhibition than do noxious cold stimuli (49).…”

“…It requires ongoing activity in primary afferents and is most probably elicited by low-threshold mechanoreceptors (A-b fibers) (S12, S13). Moreover, even normally painful stimuli can be misinterpreted as itch in a chronic itch condition when applied directly to pruritic skin lesions (48,56).…”