Cervical dystonia (CD) is the most common isolated dystonia in adults. Cervical dystonia symptoms can in most patients be managed well by botulinum toxin (BTX) injections, and supporting treatment measures. However, one-fifth to one-third of patients do not obtain sufficient relief from long-term BTX therapy, resulting in reduced quality of life. Deep brain stimulation (DBS) is a treatment method in which electrodes are surgically implanted permanently in the brain to modulate brain networks and function. In cervical dystonia, DBS of the postero-ventral part of the internal globus pallidus (GPi-DBS) has been established as an effective treatment for severe cases. However, the outcome of GPi-DBS in cervical dystonia has been reported mostly in some smaller series with up to 3 years follow-up. Thus, there is a lack of documentation of outcome of GPi-DBS in CD beyond 3 years of treatment and in larger patient materials. In this study the investigators will perform a long-term follow-up study of patients who were operated with a DBS-device targeting the GPi bilaterally, and who have been treated with chronic GPi-DBS for a minimum of 3 years. The investigators will measure the severity of symptom burden and quality of life with validated rating scales. The investigators will compare this DBS-treated cohort with an age- and gender matched group of CD patients who are receiving the standard treatment with botulinum neurotoxin (BoNT) injections and have been treated for at least 3 years as well. The investigators hypothesize that the DBS-treated group will have a significantly lower burden of symptoms at long-term follow-up than the BoNT treated group.
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Total score of the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS).
Timeframe: In the DBS-group: After 3-17 years of continuous GPi-DBS. In the BoNT-group: After minimum 3 years of regular BoNT injections (minimum 12 injection cycles), and 4-6 weeks after the last injection.