STIMULATION OF THE VENTRAL INTERMEDIATE THALAMIC NUCLEUS IN TREMOR DOMINATED PARKINSONS-DISEASE AND ESSENTIAL TREMOR

Based on Benabid's experimental and clinical findings that low-frequen cy (50 Hz) electrical stimulation of the ventral intermediate thalamic nucleus may increase tremor, while higher frequencies (>100 Hz) lend to suppression of the tremor, we implanted a stimulation electrode in 33 thalami among 27 patients. Six patients were implanted bilaterally. 23 suffered from Parkinson's disease, 4 from essential tremor. All pa tients had a drug-resistant tremor. The Vim target was calculated base d on stereotactic ventriculography. An intra-operative neurophysiologi cal target control was performed on all patients. After a monopolar (1 2 thalami) or quadripolar (21 thalami) lead was implanted we then conn ected it to a percutaneous extension lead. In the days following the s urgery a test stimulation was performed. In all but one patient stimul ation resulted in a suppression of the tremor. In a second procedure, a pulse generator (ITREL II; MEDTRONIC) was implanted and connected su bcutaneously to the thalamic lead. After implantation of the pulse gen erator all patients stimulate chronically while some turn off the stim ulator at night. In 21 thalami total suppression of tremor was observe d, 6 showed major improvement, 4 only minor improvement. There was no significant effect on any other existing symptom of Parkinson's diseas e. Due to the proximity of Vim to the sensory thalamus the majority of the patients (27 thalami) report slight temporary paraesthesias when the pulse generator is turned on. Two report permanent paraesthesias w hen stimulation is on. In 4 cases a slight dysarthria occurs under sti mulation. In 2 the dysarthria is marked. In one case dysequilibrium oc curs under stimulation. All these side effects are reversible when sti mulation is turned off. In 3 patients, the lead was displaced due to a n insufficient lead fixation, thus making a second procedure necess;uy to correct the electrode position. We had one complication due to ble eding at the burr hole side. Follow-up ranges from 3 to 48 months. So far in no cases has the effect of stimulation worn off. In conclusion we regard Vim neurostimulation as an effective and safe alternative to conventional thalamotomy and recommend that it should be considered i n cases in which drug therapy has failed to affect Parkinsonian or ess ential tremor. Moreover, we believe that this procedure is a less inva sive and equally efficient alternative to classic thalamotomy and thus should be given preference.