BACKGROUND: Severe forms of primary dystonia are difficult to manage medically. 
We assessed the safety and efficacy of pallidal neurostimulation in patients 
with primary generalised or segmental dystonia prospectively followed up for 5 
years in a controlled multicentre trial.
METHODS: In the parent trial, 40 patients were randomly assigned to either sham 
neurostimulation or neurostimulation of the internal globus pallidus for a 
period of 3 months and thereafter all patients completed 6 months of active 
neurostimulation. 38 patients agreed to be followed up annually after the 
activation of neurostimulation, including assessments of dystonia severity, 
pain, disability, and quality of life. The primary endpoint of the 5-year 
follow-up study extension was the change in dystonia severity at 3 years and 5 
years as assessed by open-label ratings of the Burke-Fahn-Marsden dystonia 
rating scale (BFMDRS) motor score compared with the preoperative baseline and 
the 6-month visit. The primary endpoint was analysed on an intention-to-treat 
basis. The original trial is registered with ClinicalTrials.gov (NCT00142259).
FINDINGS: An intention-to-treat analysis including all patients from the parent 
trial showed significant improvements in dystonia severity at 3 years and 5 
years compared with baseline, which corresponded to -20·8 points (SD 17·1; 
-47·9%; n=40) at 6 months; -26·5 points (19·7; -61·1%; n=31) at 3 years; and 
-25·1 points (21·3; -57·8%; n=32). The improvement from 6 months to 3 years 
(-5·7 points [SD 8·4]; -34%) was significant and sustained at the 5-year 
follow-up (-4·3 [10·4]). 49 new adverse events occurred between 6 months and 5 
years. Dysarthria and transient worsening of dystonia were the most common 
non-serious adverse events. 21 adverse events were rated serious and were almost 
exclusively device related. One patient attempted suicide shortly after the 
6-month visit during a depressive episode. All serious adverse events resolved 
without permanent sequelae.
INTERPRETATION: 3 years and 5 years after surgery, pallidal neurostimulation 
continues to be an effective and relatively safe treatment option for patients 
with severe idiopathic dystonia. This long-term observation provides further 
evidence in favour of pallidal neurostimulation as a first-line treatment for 
patients with medically intractable, segmental, or generalised dystonia.
FUNDING: Medtronic.