Displacement-Guided Focused Ultrasound of the Median Nerve Modulates Somatosensory Evoked Potentials in Humans.

Abstract

This study investigated the attenuation of somatosensation in healthy subjects (n = 18) and subjects with carpal tunnel syndrome (CTS) (n = 6) via displacement-guided median nerve focused ultrasound (FUS). Somatosensory evoked potentials (SSEPs), pain, stiffness, and numbness were used as markers of sensation. Electroencephalography (EEG) was used to evaluate changes in electrically-induced SSEPs when paired with FUS. Subjects underwent 1000 (healthy population) or 500 (CTS population) surface electrical pulses at a maximum rate of 1 Hz to the median nerve to invoke a thumb twitch. Half of these pulses were paired with 5 ms of upstream median nerve sonication from a 1.1 MHz transducer at 1.8 or 2.9 MPa derated peak-positive pressure. On-nerve sonication reduced the amplitude of SSEPs at both pressures. Reductions in beta and low-gamma frequency power occurred in healthy subjects and increases in alpha power occurred in CTS subjects. CTS subjects who received on-nerve sonication reported an average pain reduction of 40.6%. Off-nerve sonication did not reduce SSEP amplitudes or CTS symptoms. Median nerve displacement was correlated with SSEP reductions. Sonication of the median nerve can attenuate SSEPs, potentially in a displacement dose-driven manner. Symptom reduction in CTS subjects lasted 1-3 days post-procedure. Nerve targeting is essential to ensure therapeutic efficacy. This study is the first to demonstrate that peripheral nerve FUS modulates somatosensory-evoked potentials in humans. FUS attenuated neuropathic pain and stiffness related to median nerve entrapment, illustrating the potential analgesic effects of the procedure.