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Background: Despite the fact that severe itch is common in many dermatological diseases, the therapeutic arsenal against itching is limited. From neurophysiological experiments, using a new technique termed cutaneous field stimulation, it is known that acute itch can be effectively relieved by stimulation of cutaneous nociceptors., Methods: We tested the effects of cutaneous field stimulation (25 min, 16 electrodes, 4 Hz per electrode, up to 0.8 mA) on chronic itch due to atopic dermatitis. Transcutaneous electrical nerve stimulation (100 Hz, up to 26 mA) was used for comparison. In 27 patients, itch was measured just prior to, during and at regular intervals up to 12 h after either type of treatment., Results: Both treatments augmented the itch sensation during ongoing stimulation, presumably reflecting an altered sensory processing in the somatosensory pathways of chronic itch patients. However, after cessation of cutaneous field stimulation, but not transcutaneous electrical nerve stimulation, the itch sensation was significantly depressed for up to 7 h. The peak inhibitory effect (about 25% of control) was reached between 1 and 5 h poststimulation. Neither treatment had any significant effect on alloknesis, as measured before and 10 min after stimulation., Conclusion: It is concluded that cutaneous field stimulation strongly depresses chronic itch, and is a potentially useful symptomatic treatment of itch.

We have recently shown that stimulation, through a multi-electrode array, of thin nerve fibres close to the dermo-epidermal junction in the skin, produces powerful inhibition of itch and, to a lesser degree, cutaneous pain in humans. Here, we have studied the induction time and frequency dependency (range 1-10Hz) of the inhibitory effects of such stimulation on itch, mechanical, and thermal pain, in 20 healthy subjects. Sixteen electrodes applied on the skin were consecutively stimulated using a method termed cutaneous field stimulation (CFS). The results show that different treatment periods with CFS were required for the induction of significant inhibitory effects on different nociceptive qualities: 1st heat pain (1 min), itch (3 min), 2nd heat pain (6 min), pinch evoked pain (8 min). Six to ten minutes stimulation sufficed to induce peak inhibitory effects on all these sensory qualities while longer stimulation (up to 40 min) did not cause significantly stronger inhibition. The effects on itch, 1st and 2nd heat pain lasted over 55 min after termination of CFS. There was no effect on prickle. No significant difference in inhibitory effects of different stimulation frequencies (1, 4 and 10Hz/electrode) was found. The induction time and effective stimulation frequencies may suggest that the underlying mechanisms are similar to those of long term depression (LTD) previously described in the spinal cord in animal experiments.

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.