Bain_edit_EU Neurology 11/03/2010 13:19 Page 81
Deep Brain Stimulation for Dystonia
and ventralis oralis posterior) DBS in writer’s cramp.
27
There are some Table 1: Typical Settings for Globus Pallidus
reports that suggest that the subthalamic nucleus is an effective
Internus Stimulation in 20 Patients with Dystonia
Treated at the Imperial College Movement Disorders
target for DBS in primary and tardive dystonia.
28
It is argued that
and Neuromodulation Unit
subthalamic nucleus DBS uses less power and thus prolongs battery
life, has immediately beneficial effects (compared with the usual delay
Voltage Pulse Width Frequency
of about six months seen after GPi DBS) and is clinically as effective.
(V) (µs) (Hz)
However, the overwhelming evidence in the published literature on
Mean 4.8 180 154
DBS for dystonia is based on the GPi as the target. Median 4.5 195 135
Range 3.0–7.0 90–300 135–180
Programming Deep Brain Stimulation in
Dystonic Patients Figure 1: Magnetic Resonance Image
Post-operative programming of the implanted pulse generator
Demonstrating a Left-sided Globus Pallidus
following electrode implantation in GPi is more difficult in dystonia
Internus Electrode In Situ (arrow)
than other conditions (for example tremor or Parkinson’s disease).
This is because the beneficial effects of GPi stimulation take time to
appear. Typically, the benefit of GPi stimulation accrues over a period
of about six months, but may take up to a year to optimise. In general,
some pain relief occurs first, usually within days, and then the phasic
components improve before the tonic components of the dystonia.
29
As surgery is usually performed under general anaesthesia, limited
data will be available from theatre to guide post-operative
programming. Currently, the most posteroventral portion of GPi is
considered to be the optimum site for stimulation in dystonia and
contact closest to this area is usually the deepest.
In the Charing Cross Hospital unit, three days after electrode
implantation, each contact is tested with monopolar stimulation set at
135Hz and at a pulse width of 90µs. The voltage is gradually turned up
to 4.0V or until adverse effects occur. These may include:
The right-sided electrode had become displaced and required replacement surgery because
visual ‘phosphenes’ (flashes);
of an acute rebound in the patient’s dystonic symptoms.
capsular effects (pulling or cramp in the contralateral side of the
face or limbs); months).
31
The beneficial effects of pallidal DBS in primary generalised
a tight feeling in the mouth; dystonia seem to be durable. Several studies include follow-up data at
dysarthria; two years, and there are descriptions of small numbers of patients
non-specific giddiness; and followed post-operatively for over five years.
gait disturbances.
Prospective, Controlled Data
The lowest contact on each electrode with which no adverse effects Recent data from prospective, controlled trials provide more
are experienced on stimulation, or the highest threshold to adverse robust evidence for the benefit of pallidal DBS in primary generalised
effects is detected, is then chosen for stimulation. dystonia.
19–22
The improvements demonstrated were less than those
quoted in several of the uncontrolled studies and there was a
The patients are subsequently monitored regularly as outpatients to significant degree of ‘response variability’, which was largely
assess progress. Increases in the voltage, pulse width or frequency, unexplained. A multicentre French study assessed bilateral pallidal
generally in that order, are considered if a suboptimal therapeutic DBS in 22 severely impaired patients with PGD.
21,22
Controlled
effect occurs. Typical long-term stimulation parameters in patients videotaped assessments were performed in a randomised, double-
with dystonia treated with GPi stimulation at the Charing Cross blind manner three months after surgery with the stimulators turned
Hospital unit are shown in Table 1. ‘off’ or ‘on’. Uncontrolled assessments followed at six, 12 and 36
months. At three months, there were significant improvements in
Results of Globus Pallidus Stimulation in BFMDRS motor and disablility scale scores compared with baseline,
Primary Generalised Dystonia when the stimulators were activated. When ‘on’ and ‘off’ stimulator
Uncontrolled Data conditions were compared, BFMDRS motor scores were improved
Early reports described improvements of up to 90% in the movement during stimulation but no significant change was detected in the total
section of the BFMDRS, with the most benefit occurring in children BFMDRS disability score. At one year, patients had improved by 54.6%
with the DYT-1 deletion.
11,30
In subsequent case series, benefit in the in BFMDRS motor and 44% in BFMDRS disability scores compared
order of 40–70% was seen and DYT-1 status did not appear to with baseline. Motor improvement was maintained at three years
influence the degree of improvement.
10,17,23
Benefit may occur within (mean improvements in the BFMDRS motor and disability scores of 58
hours of stimulation but is more often delayed, with progressive and 46%, respectively). Improvement in overall quality of life was
improvement seen over months (tending to plateau after about six noted at one year and maintained at three years. Cognition and mood
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