DBS of the thalamus has largely replaced thalamotomy as the preferred surgery for the treatment of medication resistant tremor. There are multiple reports demonstrating a significant reduction in tremor in 63% to 95% of patients receiving thalamic DBS for parkinsonian tremor (8-11); however, currently, it is rarely used for PD as the majority of the studies have reported that even though tremor is markedly improved, other symptoms continue to progress and cause significant disability (12,13). Therefore, this procedure is restricted to PD patients whose primary disability is tremor.
Several studies have demonstrated long-term benefit in PD tremor with thal-amic DBS. Pollak et al. (14) reported 80 PD patients who had DBS of the thalamus for drug-resistant tremor. After up to seven years of follow-up (mean three years), global evaluations showed the best control for parkinsonian rest tremor and the least satisfactory control for action tremor. There was no dramatic effect on other symptoms like bradykinesia, rigidity, or dyskinesia. Lyons et al. (12) reported the results of 12 PD patients with a mean follow-up of 40 months and a maximum follow-up of 66 months. Although tremor scores continued to be improved by 87% there was a worsening of Unified Parkinson's Disease Rating Scale (UPDRS) motor scores suggesting the worsening of other parkinsonian symptoms. Finally, Pahwa et al. (13) reported a multicenter trial of 19 PD patients who received thalamic DBS (11 unilateral and 8 bilateral) and were followed up to five years after surgery. There was a mean improvement in tremor of 85% in the targeted limb for the unilaterally operated patients and for bilaterally operated patients there was a 100% improvement in tremor on the left side and 90% on the right side. There were no improvements in symptoms other than tremor and it was concluded that thalamic DBS has limited use in the surgical treatment of PD.
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