Selective nociceptive modulation using a novel prototype of transcutaneous kilohertz high-frequency alternating current stimulation: a crossover double-blind randomized sham-controlled trial.

Background: Kilohertz high-frequency alternating current (KHFAC) stimulation has demonstrated to induce rapid and reversible nerve blocks without causing nerve damage. Previous studies have explored frequency-dependent effects using a transcutaneous approach in humans from 5 to 20 kHz. Nevertheless, its application in humans is limited by the lack of stimulators approved for frequencies above 20 kHz. Therefore, this study aimed to assess the effects and safety of transcutaneous KHFAC stimulation using a novel prototype stimulator, comparing interventions at 30, 40, and 50 kHz to sham stimulation on experimental pain, sensory, motor, and neurophysiological outcomes.

Methods: A randomized, double-blind, sham-controlled crossover study involving 34 healthy participants was conducted. Four interventions (30, 40, 50 kHz, and sham) were administered, and stimulation was applied for 20 min to the median nerve of the non-dominant hand. A prototype stimulator capable of delivering frequencies between 1 and 50 kHz, with a maximum peak-to-peak output current intensity of 400 mA was designed. The intensity applied during the stimulation was below motor threshold, evoking a 'strong but comfortable' tingling sensation. Primary outcomes included heat pain threshold (HPT), pressure pain threshold (PPT), and adverse effects. The secondary outcomes included static two-point discrimination sensitivity, isometric pinch strength, and median sensory nerve action potential (SNAP).

Results: Compared with the sham stimulation, all the active interventions exhibited a significantly greater increase in the PPT during and immediately after the stimulation, while only a significant increase was observed at 40 kHz (4.1 N/cm; 95%CI 0.3 to 7.9) at 15 min post-intervention. Compared to sham stimulation, the 40 kHz intervention had a significantly greater effect on the HPT at all time points, with the greatest difference (1.4 °C; 0.6 to 2.1) occurring immediately post-intervention. Adverse effects during active interventions included petechiae, erythema, and itching, which resolved at 24 h post-intervention. For secondary outcomes, only a significant reduction in the median SNAP velocity was observed in the sham stimulation group compared to the 50 kHz group.

Conclusions: Active KHFAC stimulation, particularly at 40 kHz, delivered through a novel stimulator, effectively increased the PPT and HPT without affecting tactile or motor outcomes, inducing mild skin-related adverse effects. These findings have potential implications for people with pain-related pathologies.

Trial Registration: NCT05230836.