Vibro-tactile stimulation of the neck induces head righting in people with cervical dystonia

Introduction: Cervical dystonia (CD) is characterized by involuntary neck muscle spasms that lead to abnormal head movements or postures. It is associated with somatosensory (tactile and proprioceptive) dysfunction. Here we tested whether vibro-tactile stimulation (VTS) of the cervical muscles constitutes a non-invasive form of neuromodulation of the somatosensory system that can provide temporary symptom relief for people with CD. Material and method: In a multi-centre study, 67 CD patients (44 female) received VTS to sternocleidomastoid and/or trapezius muscles for up to 45 min under 9 different stimulation conditions. Retention was assessed 1, 5 and 20 min past VTS. Head angles and neck muscle EMG were recorded. The primary outcome measure was a head angle index (HAI), a composite measure reflecting the head deviation across the three axes of the head. Results: After identifying the most effective VTS condition for each participant, analysis showed that 85 % (57/67) of participants experienced an improvement in HAI of at least 10 % during the application of VTS. HAI improved by 50 % or higher in 26/67 of participants. For those responding to VTS, the effects tended to decay within 20 min. For the different CD phenotypes several stimulation sites could induce similarly large relative improvements in head posture. Conclusion: The study provides first systematic evidence that cervical VTS can induce fast-acting improvements in abnormal head posture in patients with CD. It demonstrates that a stimulation of somatosensory afferent networks modulates the innervation of dystonic muscles. It highlights the potential of cervical VTS as an adjuvant, non-invasive neuromodulation treatment in CD.