Comparison of the Efficacy of Double Monopolar Versus Interleaving Stimulation Modes for Pallidal Deep Brain Stimulation

Background:

For the treatment of drug-refractory dystonia, bilateral pallidal deep brain stimulation (GPi-DBS) is proven to be an efficient option. On average, 40-55% improvement on dystonia rating scales (DRS) could be achieved according to the results of multicenter trials lasting for years. However, a considerable portion (10-25%) of the patients experience minimal alleviation despite of good electrode placement. These patients can be regarded as non-responders to GPi-DBS defined as having either limited improvement (< 25% on DRS) or worsening. Besides adjusting the amplitude, frequency or pulse-width of stimulation, one can change the electrode configuration from the commonly applied single monopolar stimulation mode (one contact on the electrode is negative) to either double monopolar stimulation (two -usually adjacent- negative contacts on the electrode are stimulated with same amplitude and pulse-width values) or bipolar stimulation mode (one contact on the electrode is positive) in case of unsatisfactory outcomes. Although these techniques had been utilized in multicenter trials, non-responsiveness to GPi-DBS did occur. Recently the investigators have reported in the Movement Disorders that the newly introduced interleaving stimulation mode was superior to single or double monopolar stimulation in four patients who had initially (6-12 months after implantation) limited response to GPi DBS.

Aims of the study:

To systematically compare the efficacy and the side-effect profile of double monopolar stimulation mode to those of interleaving stimulation mode in a prospective, randomized, double-blind, and cross-over study.

Methods:

The investigators would enroll 20-25 patients with drug refractory segmental or generalized primary dystonia undergoing bilateral GPi-DBS implantation within a 2-3 year time frame. The inclusion and exclusion criteria would follow those of the study of Kupsch et al.

Inclusion criteria

• ages of 7 and 75 years
• marked disability owing to primary generalized or segmental dystonia, despite optimal pharmacologic treatment
• disease duration of at least 5 years.

Exclusion criteria

• previous brain surgery;
• cognitive impairment (< 120 points on the Mattis Dementia Rating Scale)
• moderate-to-severe depression (> 25 points on the Beck Depression Inventory)
• marked brain atrophy as detected by magnetic resonance imaging
• other medical or psychiatric coexisting disorders that could increase the surgical risk or interfere with completion of the trial