Comparative connectivity correlates of dystonic and essential tremor deep brain stimulation.

The pathophysiology of dystonic tremor and essential tremor remains partially understood. In patients with medication-refractory dystonic tremor or essential tremor, deep brain stimulation (DBS) targeting the thalamus or posterior subthalamic area has evolved into a promising treatment option. However, the optimal DBS targets for these disorders remains unknown. This retrospective study explored the optimal targets for DBS in essential tremor and dystonic tremor using a combination of volumes of tissue activated estimation and functional and structural connectivity analyses. We included 20 patients with dystonic tremor who underwent unilateral thalamic DBS, along with a matched cohort of 20 patients with essential tremor DBS. Tremor severity was assessed preoperatively and approximately 6 months after DBS implantation using the Fahn-Tolosa-Marin Tremor Rating Scale. The tremor-suppressing effects of DBS were estimated using the percentage improvement in the unilateral tremor-rating scale score contralateral to the side of implantation. The optimal stimulation region, based on the cluster centre of gravity for peak contralateral motor score improvement, for essential tremor was located in the ventral intermediate nucleus region and for dystonic tremor in the ventralis oralis posterior nucleus region along the ventral intermediate nucleus/ventralis oralis posterior nucleus border (4 mm anterior and 3 mm superior to that for essential tremor). Both disorders showed similar functional connectivity patterns: a positive correlation between tremor improvement and involvement of the primary sensorimotor, secondary motor and associative prefrontal regions. Tremor improvement, however, was tightly correlated with the primary sensorimotor regions in essential tremor, whereas in dystonic tremor, the correlation was tighter with the premotor and prefrontal regions. The dentato-rubro-thalamic tract, comprising the decussating and non-decussating fibres, significantly correlated with tremor improvement in both dystonic and essential tremor. In contrast, the pallidothalamic tracts, which primarily project to the ventralis oralis posterior nucleus region, significantly correlated with tremor improvement only in dystonic tremor. Our findings support the hypothesis that the pathophysiology underpinning dystonic tremor involves both the cerebello-thalamo-cortical network and the basal ganglia-thalamo-cortical network. Further our data suggest that the pathophysiology of essential tremor is primarily attributable to the abnormalities within the cerebello-thalamo-cortical network. We conclude that the ventral intermediate nucleus/ventralis oralis posterior nucleus border and ventral intermediate nucleus region may be a reasonable DBS target for patients with medication-refractory dystonic tremor and essential tremor, respectively. Uncovering the pathophysiology of these disorders may in the future aid in further improving DBS outcomes.

Possible seizure suppression via deep brain stimulation of the thalamic ventralis oralis posterior nucleus.

Surgical treatment of intractable epilepsy with deep brain stimulation (DBS) has been shown to be of therapeutic benefit in some patients and with the recent publication of a randomised control study its use is likely to increase in the future. We describe a patient who developed a focal epileptic seizure within a few seconds of momentarily turning off the DBS stimulator in the nucleus ventralis oralis posterior, with which she was successfully treated for tremor. The seizure was the result of a newly diagnosed primary brain tumor. We suggest that the nucleus ventralis oralis posterior may be another thalamic target of DBS in epilepsy.

Dual electrode thalamic deep brain stimulation for the treatment of posttraumatic and multiple sclerosis tremor.

OBJECTIVE: To report the results of ventralis intermedius nucleus/ventralis oralis posterior nucleus (VIM) plus ventralis oralis anterior (VOA)/ventralis oralis posterior (VOP) thalamic deep brain stimulation (DBS) for the treatment of posttraumatic and multiple sclerosis tremor. OBJECTIVE: The treatment of posttraumatic tremor and multiple sclerosis tremor, by either medication or surgery, has proven difficult. Lesions and DBS have had mixed and somewhat disappointing results. Previously, we reported the use of two DBS electrodes (one at the VIM/VOP border and one at the VOA/VOP border) as effective for the treatment of posttraumatic tremor in a single patient. In this study, we report the results of this technique on four patients. METHODS: Four patients with either posttraumatic tremor (n = 3) or multiple sclerosis tremor (n = 1) underwent placement of two DBS electrodes (one at the VIM/VOP border and one at the VOA/VOP border). Patients underwent preoperative testing and testing at a minimum of 6 months after implantation in four conditions: On VIM DBS/On VOA/VOP DBS; On VIM DBS/Off VOA VOP DBS (5 h DBS washout); Off VIM DBS/Off VOA/VOP DBS (12 h overnight washout); and Off VIM DBS/On VOA/VOP DBS (5 h DBS washout). RESULTS: Each of the patients showed improvements in all four conditions when compared with the baseline. All of the improvements were maintained with chronic DBS, without tremor rebound. An analysis was performed to determine whether each condition was associated with symptom reduction (percentage change). The percentage reduction was significant for each condition and measure, despite the small number of participants. For the total tremor rating scale score, the Off VIM/Off VOA/VOP condition yielded less symptom reduction than the On VIM condition or the On VOA/VOP condition. The On VIM and On VOA/VOP conditions did not differ significantly from each other in terms of contralateral upper extremity symptoms or total clinical score. Activation of both the VIM and VOA/VOP electrodes was associated with the greatest symptom reduction. CONCLUSION: Tremors, such as those examined in this study, that are refractory to medications and have a poor response to VIM DBS monotherapy, may respond favorably to VIM plus VOA/VOP DBS. Two electrodes may be better than one for the treatment of certain disorders; however, more study will be required to confirm this hypothesis.