gms | German Medical Science

Objective: To evaluate the effects of deep brain stimulation of the subthalamic region and nucleus ventralis intermedius on postural and kinetic components of dystonic tremor.

Method: Sequential interleaved monopolar stimulation of the nucleus subthalamicus (STN) and nucleus ventralis intermedius (Vim) was performed after inadvertent bilateral implantation of deep brain stimulation electrodes (Model 3387, Medtronic Inc.) for treatment of kinetic-dominant tremor. Post-implantation MRI confirmed the location of the electrode lower contacts in STN and of the electrode upper contacts in Vim, thus providing a unique opportunity to dissect the effects of electrical stimulation of both nuclei on various tremor components in the same patient. Changes in acceleration of the dominant upper extremity were used as an indirect measure of postural and kinetic tremor, sampled at 70 Hz using an accelerometer, high-pass filtered and analyzed using custom-build Igor Pro (Wavemetrics, Portland OR) routines. Analysis was performed along the accelerometer axis exhibiting the greatest variation. To allow for direct comparison, alternative monopolar (assuming uniform radial distribution of the electric field) stimulation of the electrode contacts located in STN and Vim was interspersed with periods of no stimulation. The stimulation parameters were chosen to provide similar average power consumption for a train of rectangular pulses at both STN and Vim. Each stimulation period was concluded by performing an quality-of-life tremor assessment.

Results: Power spectral density of the postural accelerometer time series showed peaks at frequencies of 3.2 Hz (Vim) and respectively at 3.4 Hz (STN) with consistent reduction of signal power for higher frequencies, suggesting a high-pass filtering effect of the electrical stimulation of both nuclei on postural tremor. Interestingly spectral power was lower at each given frequency in the case of STN stimulation compared to Vim. Regarding kinetic tremor components, STN stimulation showed a significant reduction of the peak tremor frequency (1.31 Hz) compared to Vim stimulation (3.39 Hz).

Conclusions: Although an established target for controlling rigidity and bradykinesia in Parkinson’s disease, electrical stimulation of STN showed similar short-term effects on postural tremor components and even significantly better control of kinetic tremor components compared to Vim electrical stimulation.