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-frequency (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 patients had a drug-resistant tremor. The Vim target was calculated based on stereotactic ventriculography. An intra-operative neurophysiological target control was performed on all patients. After a monopolar (12 thalami) or quadripolar (21 thalami) lead was implanted we then connected it to a percutaneous extension lead. In the days following the surgery a test stimulation was performed. In all but one patient stimulation resulted in a suppression of the tremor. In a second procedure, a pulse generator (ITREL II; MEDTRONIC) was implanted and connected subcutaneously to the thalamic lead. After implantation of the pulse generator all patients stimulate chronically while some turn off the stimulator at night. In 21 thalami total suppression of tremor was observed, 6 showed major improvement, 4 only minor improvement. There was no significant effect on any other existing symptom of Parkinson's disease. 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 when stimulation is on. In 4 cases a slight dysarthria occurs under stimulation. In 2 the dysarthria is marked. In one case dysequilibrium occurs under stimulation. All these side effects are reversible when stimulation is turned off. In 3 patients, the lead was displaced due to an insufficient lead fixation, thus making a second procedure necess;uy to correct the electrode position. We had one complication due to bleeding 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 in cases in which drug therapy has failed to affect Parkinsonian or essential tremor. Moreover, we believe that this procedure is a less invasive and equally efficient alternative to classic thalamotomy and thus should be given preference.