Intermuscular coherence during co-contraction eliciting tasks as a biomarker for dystonia and GPi-DBS efficacy

OBJECTIVE: Clinical rating scales often fail to capture the full spectrum of dystonic symptoms. Deep brain stimulation of the globus pallidus interna (GPi-DBS) effectively treats dystonia, but response variability necessitates a reliable biomarker. Intermuscular coherence (4-12 Hz) has been linked to abnormal activity in the cortico-basal ganglia-thalamo-cortical (CBGTC) loop and may serve as an objective measure of dystonia and GPi-DBS effectiveness.

METHODS: A retrospective cohort study included 12 dystonia patients undergoing GPi-DBS implantation. Clinical rating scales and a neurophysiological assessment were performed before and one year post-DBS. Coherence in the 4-12 Hz range was analyzed from electromyography (EMG) of antagonistic arm muscles. Comparisons were made between patients with and without arm dystonia, t-tests evaluated the differences between pre- and post-DBS, and correlations between coherence and clinical scales were performed.

RESULTS: Seven patients with arm dystonia appeared to have higher pre-operative intermuscular coherence compared to those without. Coherence was significantly decreased after GPi-DBS in the arm dystonia group. No strong correlations were found between coherence and clinical rating scales.

CONCLUSION: Intermuscular coherence is present in dystonic muscles and decreases following GPi-DBS. Correlations with motor scores were inconclusive due to patient heterogeneity and ill-fitting clinical scales.

SIGNIFICANCE: Intermuscular coherence has potential to aid GPi-DBS patient selection and optimization but larger studies are needed to validate its use.