Article
Thalamic deep brain stimulation for tremor therapy: anatomical location of active electrode contacts and clinical outcome
Tiefenhirnstimulation im motorischen Thalamus zur Tremortherapie: anatomische Lokalisation des aktiven Elektrodenkontakts und funktionelles Ergebnis
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Published: | May 8, 2006 |
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Objective: To correlate the anatomical location of active electrode contacts with the improvement of tremor gained by Deep-Brain-Stimulation (DBS).
Methods: From 02/1996 through 09/2004 40 consecutive pts. were treated with DBS for arm tremor. Two contacts of the quadrupolar electrodes (n=30) were placed inside the VIM nucleus and two contacts in the area of the zona incerta/Forel’s field. Postoperatively, coordinates of the electrode contacts were taken from stereotactic x-ray control images, retransferred into the treatment planning MRI, and the anatomical position was defined in relation to the ACPC line. Patients with complete data sets were selected for correlation of the active electrode contact with the clinical outcome using a semi quantitative scale (essential tremor (ET) 9 pts., multiple sclerosis (MS) pts. 11).
Results: Active contacts projected onto the base of the VIM or below in 16/30 electrodes and were found in a range of 1-4.9 mm above the ACPC-line in 14/30 cases. DBS (monopolar mode: 16/30 electrodes, bipolar mode: 14/30 electrodes, impulse generator setting (median values): 3.25 A, 60.0 ms, 130.0 Hz) gained functional useful tremor improvement in 7/9 ET cases and in 7/11 MS pts. Functional improvement correlated with contacts located inside the motor thalamic nucleus in 11/20 electrodes and with contacts in the subthalamic area in 9/20 electrodes.
Conclusions: Extension of the lesion from the thalamic motor nuclei into the subthalamic region has been considered to be an important step in achieving significant tremor relief after thalamotomy. In analogy, for DBS we positioned two of four electrode contacts below the Vim nucleus. In the patients analyzed here, major tremor improvement was achieved with almost equal success if the stimulation contacts were inside the nucleus or in the subthalamic area. This observation is not in line with the hypothesis that the effects of high-frequency stimulation are mainly mediated through afferents entering a particular target and/or through fibers tracts running in close vicinity to this area.