Deep Brain Stimulation for Primary Torsion Dystonia
Abstract & Commentary
By Panida Piboolnurak, MD, Assistant Professor, Department of Neurology and Neuroscience, Weill Medical College, Cornell University; Dr. Piboolnurak reports no financial relationship relevant to this field of study.
Synopsis: Deep brain stimulation of the internal globus pallidus at 60 Hz is effective treatment for primary dystonia.
Source: Alterman RL, et al. Sixty hertz pallidal deep brain stimulation for primary torsion dystonia. Neurology. 2007;69: 681-688.
Deep brain stimulation (dbs) of the globus pallidus interna (GPi) is an effective therapy for primary dystonia. In most case series, high frequencies (130-185 Hz) and wide pulse width (120-450 mcsec) were used based on the experience in Parkinson's disease and essential tremor. This can result in excessive battery consumption and may cause muscle contractions because of current spreading to the adjacent internal capsule.
Alterman and colleagues reported their experience in using 60 Hz stimulation in 15 consecutive patients with primary dystonia (12 men and 3 women). Twelve had DYT1 gene mutation (9 men and 3 women). Median age at the time of surgery was 20 years, with a median symptom duration of six years. The electrodes were placed in posteroventral GPi (bilateral in 13 patients and unilateral in 2 patients). The stimulation was set at 60 Hz in all patients. The stimulating contacts were selected from four available contacts (0-3) on each side based on the clinical response and tolerability. The initial voltage and pulse width were set at 2.5 volts and 120 mcsec based on their experience. Voltage or pulse width was then adjusted monthly or bimonthly to maximize the benefit or to reduce adverse effects. Frequency was kept constant at 60 Hz.
The motor subscales of Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-M) and disability subscales (BFMDRS-D) were employed for clinical assessment in an open-label fashion at baseline (within 1 week of surgery), and at 1, 3, 6, and 12 months after the initial programming. At the baseline, the median BFMDRS-M and BFMDRS-D scores were 35 and 8, respectively. Median improvement in BFMDRS-M was 38%, 76%, 82%, and 89% at 1, 3, 6, and 12 months, respectively. Median improvement in BFMDRS-D was 25%, 64%, 70%, and 75% at 1, 3, 6, and 12 months, respectively.
The outcome correlated with age at the time of surgery (better in patients younger than 21) and the duration of symptoms, but did not correlate with DYT1 status, age at disease onset, disease severity, or gender. There were no differences in the outcome at one year between patients with phasic and tonic dystonia. However, patients with phasic dystonia had a trend toward better improvement at one month. Of 13 patients who were taking medications for dystonia preoperatively, 7 were able to stop medications at their last follow-up (12-30 months). Six patients were able to reduce medications by at least 50%. The intrathecal baclofen pump required by one patient could be removed.
Of 28 electrodes, 27 were unipolar stimulation (11 with single monopolar, 14 with double contiguous monopolar, and 2 with triple monopolar) with a mean amplitude of 3.0 ± 0.3 volts. The most common contact used was contact 1 (37%), followed by contacts 2, 0, and 3. Pulse widths at the last follow-up ranged from 120 to 270 mcsec. The average battery consumption was 55 microAmp, which was approximately half of what was observed in stimulation with higher frequency according to the authors' unpublished observations.
Commentary
GPi DBS is an effective treatment for primary dystonia. However, there was no established guideline for the electrical parameter setting in dystonia. Based on experience with Parkinson's disease, high frequency stimulation has been used. Wide pulse width also tends to be used due to a belief that a wide pulse width is required to cover the larger dimensions of GPi compared to the subthalamic nucleus. Combination of high frequency and high pulse width will shorten the battery life and can cause muscle contractions due to electrical current spreading to the adjacent internal capsule. This study provided the evidence that lower frequency (60 Hz) can be effective in dystonia. Although the pulse width used in this study is not in the highest end, it is still in the higher range. Without a direct comparison with higher frequency settings, it is difficult to know whether higher frequency could be more effective than 60 Hz stimulation. Future studies with direct comparison among different pulse widths and frequencies will be required to provide a guideline for the best parameter setting.
Deep brain stimulation of the internal globus pallidus at 60 Hz is effective treatment for primary dystonia.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content