Dystonia is a chronic neurological condition that impacts the quality of life due to decreased mobility, social repercussions caused by others's perception of abnormal involuntary movement and frequent pain. Botulinum toxin has been shown to be effective in reducing pain in dystonia. However, many patients remain painful despite the injections, especially when the decrease in the effect of the latter, performed every 3 months on average. Despite frequent use of TENS in pain relief, only a few small studies studying TENS in dystonia were published and none of them reported TENS effects on dystonic pain using sensory threshold.

This study aimed to quantify the efficacy and tolerance of TENS in the indication of pain related to dystonia, focusing on cervical dystonia which is the most common form of dystonia.

TENDYS (TENs use in cervical DYStonia) is an observational, prospective, single arm, monocentric study including subjects between September 2019 and July 2020 with cervical dystonia treated or not with botulinum neurotoxin (BoNT) type A at the Nancy Regional University Hospital.

All patients who benefited from a simple follow-up or injections of BoNT every 3 or 4 months for a painful cervical dystonia were proposed the use of TENS during a neurologic consultation with one of two specialist physicians trained to cervical dystonia. Patients who accepted had to give informed consent and were re-evaluated about 1 month later to ensure that pain persisted and to have a demo of TENS. The electro-stimulator was delivered to posterior cervical muscles over or close to the painful site, according to a Conventional or High frequency/Low intensity mode (Gate control). Patients were encouraged to use the machine daily, as often and long and possible, except for sleeping and driving.

Follow-up assessments of pain occurred at the consultation toxin injection 3 months later and at 4 months for all patients.

Inclusion Criteria:

• Patient having received complete information on the organization of the research and not having objected to the exploitation of the data
• patient admitted to neurology consultation for cervical dystonia treated with botulinum toxin

Exclusion Criteria:

• Patient under legal protection
• Minor patient
• Patient refusing to give consent
• Patient with exclusive radicular or truncal involvement
• Missing data or absence of established reactogenic threshold

any patient admitted to a neurology consultation for cervical dystonia treated with botulinum toxin.