Parkinson disease: deep cerebral stimulation

The effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the internal pallidum (GPi) on the parkinsonian triad and on levodopa-induced dyskinesias are very similar. The antiakinetic effect of STN DBS seems to be slightly better. On the contrary to pallidal DBS, stimulation of the STN allows to reduce dopaminergic treatment by more than 50 p. 100 on average. Moreover, the current drain is smaller in STN. Thus, the STN is a low budget target compared to the GPi. STN DBS seems to be as effective on PD tremor as stimulation of the classic thalamic target, the ventral intermediate nucleus (Vim), whereas Vim stimulation has no effect on akinesia and very little on levodopa-induced dyskinesias. Thus, the STN has become the main target nucleus for DBS in PD, which is most often performed bilaterally in one surgical procedure. There is a good correlation of the preoperative response to levodopa and postoperative effects of bilateral STN DBS and this defines the patient population. Given the large patient population, simple guidelines for patient selection are developed. The referring physician can preselect patients based mainly on age (less than 70), absence of dementia and presence of severe disability related to motor fluctuations or dyskinesias. It is the responsibility of the operating centre to determine the levodopa response, to confirm the diagnosis, to rule out contraindications and to make sure that the medical treatment cannot be further optimised. Severe surgical complications with permanent sequels are relatively rare, about 1 p. 100 per implanted side. The patient selection, the precision of the surgery and the quality of the postoperative follow-up are the three main determinants of success.