Objective: Deep brain stimulation of the globus pallidus interna (GPi-DBS) is a treatment option for medication-refractory dystonia. However, the clinical outcome after DBS-GPi is variable, in part because of insufficient patient selection criteria and suboptimal stimulation settings. The aim of this study was to explore co-contractions as a possible biomarker of dystonia severity and GPi-DBS efficacy.

Background: The EMG pattern of dystonia patients often consists of simultaneous activation of antagonistic muscles, described as co-contractions, and this can be quantified using coherence analysis. In patients with dystonia, dystonic muscle and pallidal activities are coherent over the low frequency band. For this study, we investigated the intermuscular coherence in the 4-12 Hz band of antagonistic muscle pairs as a potential biomarker of GPi-DBS in dystonia. We hypothesized that co-contractions are correlated to dystonia clinical state and could therefore function as a biomarker for DBS efficacy.

Method: The EMG of bilateral wrist flexor-extensor muscles of 16 heterogeneous dystonia patients with GPi-DBS (median age 53 years) was recorded during three standardized motor tasks (an in-out, up-down and pronation-supination movement of the wrists). Patients were measured one day prior to DBS surgery (pre-DBS) as well as one year afterwards (post-DBS). Coherence analyses were performed on the EMG signals of the antagonistic muscle pairs. Clinical performance was quantified using the motor part of the Burke Fahn Marsden Dystonia Rating Scale (BFMDRS), and correlated to the intermuscular coherence using Spearman’s rank correlation.

Results: One year after GPi-DBS, patients significantly improved on average 26% on the motor part of the BFMDRS. Intermuscular coherence significantly decreased for the in-out task (p<0.01). A significant correlation was found between pre-DBS intermuscular coherence and pre-DBS BFM-score for the in-out and up-down tasks (R=0.39 and p=0.03; R=0.39 and p=0.03, respectively). The correlation between post-DBS coherence and post-DBS BFM-score was not significant.

Conclusion: The current study showed that intermuscular coherence of antagonistic arm muscles measured in the pre-operative phase is correlated to dystonia motor severity. We propose that intermuscular coherence could be developed into a valuable biomarker of dystonia clinical state, which could help optimize GPi-DBS patient selection and may aid DBS programming.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/co-contractions-as-a-biomarker-for-dbs-efficacy-in-dystonia/