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

Objective: 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. Methods: Electroencephalography (EEG) was used to evaluate changes in electrically-induced SSEPs when paired with FUS. Subjects underwent 1,000 (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. Results: 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. Conclusion: Sonication of the median nerve can attenuate SSEPs, potentially in a displacement dose-driven manner. Symptom reduction in CTS subjects may last 1-3 days post-procedure. Nerve targeting is essential to ensure therapeutic efficacy. Significance: 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.