Stimulation of subthalamic fibre tracts reduces dyskinesias in STN-DBS

Objective: To describe the efficacy of stimulation within the subthalamic white matter for reducing dyskinesias associated with subthalamic deep brain stimulation (STN-DBS)

Aims: In some PD-patients, the postoperative management following STN-DBS is complicated by pharmacologically intractable dyskinesias. Here we report three patients, in whom additional stimulation of the most proximal contact led to significant reduction of dyskinesias.

Methods: The clinical dyskinesia rating scale (CDRS, max 28) was used to assess dyskinesias before and three months after stimulation of the most proximal contact of the quadripolar electrode. The stereotaxic coordinates of contacts (stx-coord x, y, z in mm relative to the midcommissural point) were obtained by landmark-based fusion of the post- and preoperative stereotaxic T1-sequences.

Results: Patient 1:2 months after initiation of STN-DBS, a 49 year old male developed choreatiform dyskinesias in the right leg unresponsive to usual therapeutic measures. Additional stimulation of the most proximal contact (stx-coord -12.8, 0.6, 1.7) led to a reduction of dyskinesias with a decrease in the CDRS from 6 to 2. Patient 2: 4 years following sustained efficacy of STN-DBS, a 59 year old woman had to undergo re-implantation of the left electrode because of dislocation. Following the procedure the patient developed -due to a microlesional effect- severe dyskinesias in the right leg without STN-DBS. Stimulation of the most proximal contact (stx-coord -12.7, 0.7, 0.7) led to a sustained reduction of dyskinesias (CDRS from 3 to 1). Patient 3: 6 years following bilateral fetal nigral transplantation, a 60 year old male was treated by STN-DBS which led to complete remission of OFF-period-akinesia allowing for withdrawal of all dopaminergic drugs. Disabling OFF-phase dyskinesias were reduced by bilateral stimulation of proximal contacts (stx-coord 12.6, 1.3, 0.6 and -12.7, 1.1, -02.) with a decrease of CDRS from 12 to 5. In all patients, superposition of proximal contacts onto the Schaltenbrand-Wahren-atlas revealed a location within the subthalamic white matter in vicinity to the lenticular and thalamic fasciculus which contains a significant proportion of pallidothalamic fibres.

Conclusions: Additional stimulation of contacts located within the subthalamic white matter may reduce dyskinesias secondary to STN-DBS by affecting neural activity in the pallidothalamic fibre system.