Effect of Percutaneous Electric Stimulation with High Frequency Alternating Currents on the Sensory-Motor System of Healthy Volunteers

BackgroundFormer studies investigated the application, both transcutaneous and with implanted electrodes, of high frequency alternating currents (HFAC) in humans for blocking the peripheral nervous system. The present trial aimed to assess the effect of HFAC on motor response, somatosensory thresholds, and peripheral nerve conduction, when applied percutaneously with ultrasound-guided needles at frequencies of 10 kHz and 20 kHz in healthy volunteers. MethodsA parallel, placebo-controlled, double-blind, randomized clinical trial was conducted. Ultrasound-guided HFAC at 10 kHz and 20 kHz and sham stimulation were delivered to the median nerve of 60 healthy volunteers (n=20 per group) for 20 minutes. The main assessed variables were maximum isometric flexion strength (MFFS) of the index finger, myotonometry, pressure pain threshold (PPT), mechanical detection threshold (MDT), and antidromic sensory nerve action potential (SNAP). Measurements were recorded pre-intervention, during the intervention 15 minutes after its commencement, immediately post-intervention, and at 15 minutes post-intervention.ResultsA decrease in the MFFS was observed immediately post-intervention compared to baseline, both in the 10 kHz group [-8.5 %; 95% confidence interval (CI) -14.9 to -2.1] and the 20 kHz group (-12.0%; 95%CI -18.3 to -5.6). At 15 minutes post-intervention, the decrease in the MFFS was -9.5% (95%CI -17.3 to -1.8) and -11.5% (95%CI -9.3 to -3.8) in the 10 kHz and 20 kHz groups, respectively. No changes over time were found in the sham group. The between-group comparison of changes in MFFS showed a greater reduction of -10.8% (95%CI -19.8 to -1.8) immediately post-intervention in the 20 kHz compared to the sham stimulation group. Muscle tone increased over time in both the 10 kHz and 20 kHz groups, but not in the sham group. The intergroup comparison of myotonometry showed a superior effect in the 20 kHz (6.7%, 95%CI 0.5 to 12.9) versus the sham group. No significant changes were observed in the rest of the assessed variables. ConclusionsThe ultrasound-guided percutaneous stimulation applying 10 kHz and 20 kHz HFAC to the median nerve produced reversible reductions in strength and increases in muscle tone with no adverse effects.