Table 1 Eligibility criteria

• Suffering from isolated, idiopathic or hereditary cervical dystonia for more than 2 years

• Moderate to severe symptom severity of dystonia (TWSTRS total score ≥ 20 points and TWSTRS motor score ≥ 15 points)

• Age between 18 and 75 years

• Adequate therapy response of BoNT A treatment during test injection procedure (≥ 25% reduction of points in TWSTRS motor score 4 weeks after baseline)

• Previous BoNT injection ≥12 weeks before screening visit

• Written informed consent to study participation, including patient’s agreement to undergo DBS procedure

▪ Mild dystonic symptoms (TWSTRS total score < 10 points and TWSTRS motor score < 5 points)

▪ Suffering from severe depression with ongoing suicidality (BDI > 25 points)

▪ Mild cognitive impairment (MCI) and dementia (MDRS ≤125 points)

▪ Ongoing acute psychosis

▪ Drug or alcohol abuse

▪ Pregnancy or lactation, women of childbearing age without secure contraception

▪ Illiteracy

▪ Surgical contraindication to DBS

▪ Concurrent participation in other clinical trials

▪ Any medical or psychological condition associated with the risk of insufficient compliance and/or early termination of the study