Objective: To confirm the effectiveness of thalamic DBS on focal hand dystonia, the outcome of thalamic DBS was analyzed in 4 patients with focal hand dystonia, and the effective sites in the thalamus and stimulation parameters were analyzed.

Background: Focal hand dystonia is characterized by muscle spasms and abnormal posture that disturb skilled hand movements, e.g., writing or playing an instrument. The effectiveness of deep brain stimulation (DBS) of the internal segment of the globus pallidus (GPi) in dystonia of various types has been revealed; however, the effectiveness of other targets, including the thalamus, on focal dystonia has yet to be determined.

Method: Thalamic DBS, 3 unilateral and one bilateral surgery, targeting the ventralis intermedius nucleus (Vim) was performed in 4 patients, 3 females and one male ranging in age from 22 to 61 years, with medically intractable focal hand dystonia. The patients had no family history of dystonia. They presented no significant cognitive dysfunction, no active psychiatric symptoms, and no evidence of other central nervous system diseases or other medical disorders. Their significant troubles with dystonia were difficulty in manual work in two of the patients and in playing musical instruments in the other two. Movement and functional severity were assessed using the Fahn-Marsden Evaluation Scale for Dystonia. The stimulation sites and DBS parameters for the best effectiveness were investigated.

Results: After adjusting the stimulation sites and parameters to those which were the most effective for dystonia with the avoidance of side effects, all patients regained the hand dexterity to perform the tasks they had not been able to do. The post-surgery mean scores on the Fahn-Marsden Evaluation Scale for Dystonia improved from 11.0 (6-13) to 2.0 (1-4) on the Movement Scale and from 5.3 (1-10) to 0.5 (0-2) on the Severity Scale. The best stimulation setting included monopolar stimulation with multiple contacts along the lead axis, which stimulated a relatively wide Vim area, in all patients.

Conclusion: Focal hand dystonia is greatly improved by thalamic DBS. The stimulated areas in the thalamus necessary for improvement may be a wide area of the Vim and possibly a part of the nucleus ventrooralis, suggesting that disruption of cerebellar sensory feedback adding to the basal ganglia-thalamocortical activities underlie the mechanism of focal hand dystonia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-thalamic-deep-brain-stimulation-on-focal-hand-dystonia/