Vibro-Tactile Stimulation as a Non-Invasive Neuromodulation Therapy for Cervical Dystonia: A Case Study

Introduction: Cervical dystonia (CD) is a type of focal dystonia that is characterized by involuntary neck postures. The underlying neurophysiology mechanism of CD is unknown, but there is increasing empirical evidence that motor deficits of CD are associated with somatosensory and proprioceptive deficits in the upper limb area. Vibro-tactile stimulation (VTS) is a non-invasive somatosensory stimulation approach where afferent signals from the vibrated muscle and tactile mechanoreceptors modulate cortical activity. Previous studies have shown that VTS could be an effective neuromodulation therapy for treating laryngeal dystonia. This proof-of-concept study examined the effect of VTS on alleviating the involuntary cervical muscle contractions in a female participant with intermittent torticollis. Methods: VTS was applied sequentially on four neck positions: bilateral trapezius (TRP) and bilateral sternocleidomastoid (SCM). Each VTS site was vibrated continuously for six minutes. The kinematics and underlying neck muscle activities during dystonic neck movements were examined with acceleration and surface electromyography (sEMG). To quantify the efficacy of VTS, two acceleration features and one sEMG feature were derived: (1) number of acceleration peaks per minute; (2) peak amplitude of acceleration (PAA); (3) change in power of sEMG after VTS. Results: The frequency of intermittent dystonic neck movements decreased by 60% after VTS. In addition, PAA during dystonic episodes was drastically reduced after VTS when compared to baseline. Third, the effectiveness of VTS in alleviating dystonic muscle spasms depended on the site of vibration. For this participant, the left trapezius muscle was shown as the optimal vibration site reducing sEMG signal power by 15% across all recorded muscles. Conclusion: This case study offered preliminary insight into the assumed effectiveness of neck muscle VTS as a treatment for CD. Our participant experienced pain relief after VTS with measured improvements reflected by electrophysiological and kinematic data. A systematic study with a larger sample size is required in the future to validate the effectiveness of VTS for treating symptoms in CD.