Effect of thalamic stimulation of L-Dopa induced dyskinesias - evaluation of a new target: the centromedian and parafascicular complex.

After 10 years of clinical practice (1987-1997), chronic thalamic deep brai n stimulation (DBS) is considered to be effective in the treatment of drug- resistant parkinsonian tremor. DBS has produced few side-effects, which are usually reversible. More recently, DBS has been applied to other movement disorders (akinesia and rigidity, dyskinesias, dystonia), using new targets : internal pallidum, subthalamic nucleus. These Targets have been selected on the basis of neurophysiological or anatomo-clinical data suggesting they could be effective. Control of L-Dopa peak-dose dyskinesias by thalamic ve ntralis intermedius nucleus (V.im.) stimulation has been reported by the Li lle team, but not by the Grenoble team. We therefore re-examined ail telera dioanatomical data of both teams, and compared them with the therapeutic ef fects. Location of 99 monopolar electrodes of thalamic stimulation, applied to treat parkinsonian tremor, has been retrospectively measured. The Lille team included 21 patients (22 electrodes); the Grenoble team included 52 p atients (74 electrodes). L-Dopa dyskinesias were suppressed in all 9 patien ts in Lille, and improved clearly in only 8 out of 32 patients in Grenoble. The mean center of electrodes was significantly different between both tea ms, being deeper, more posterior and medial in Lille. This did not correspo nd to the coordinates of the V.im., but seems to be closer to those of the centromedian and parafascicular complex (CM-Pf), according to stereotactic atlases. Considering only the dyskinetic patients, the therapeutic effects on L-Dopa dyskinesias were related to the differences observed in the elect rode position, but not to the team membership. Improvement of L-Dopa dyskin esias was significantly associated with deeper and more medial placement of electrodes. Retrospective analysis of ventriculographic data confirmed tha t the electrode position and therapeutic effects of DBS are strongly relate d. Our study suggested that CM-Pf stimulation could control both tremor and L-Dopa dyskinesias. This hypothesis is consistent with neuro-anatomical da ta showing that CM-Pf is connected to internal pallidum, the stimulation of which controls specifically L-Dopa dyskinesias.