Objective: To perform a systematic review on coherence analysis in dystonia. We focus on different modalities and describe the relation of abnormal coherent frequency bands to clinical features and its use in DBS treatment in dystonia patients.

Background: Increasing evidence supports the presence of pathologically increased oscillatory activity of the low frequency theta- and alpha-band (4-12 Hz) in the cortico-basal ganglia-thalamo-cortical (CBGTC) loop in dystonia: the “dystonic drive”. Coherence analysis is a measure of linear coupling between two signals and can reveal descending oscillatory activity drives that are common across motor units. Different modalities can be measured and coupled to detect the common drive: local field potentials (LFPs), electromyography (EMG) and electro-encephalography (EEG).

Method: All studies that use the mathematical technique of coherence analysis for a patient population with dystonia were included. Three authors (SL, MS and LC) assessed the eligibility of the articles. The quality of the papers was assessed with the QUADAS-2 checklist (as advised by the Cochrane Collaboration).

Results: 37 articles were included, containing data of 380 adult dystonia patients: 184 focal dystonia, 3 generalized dystonia, 33 myoclonus-dystonia and 160 non-specified dystonia patients, investigated in a heterogeneous cohort. In the selected records, six different combinations were investigated: corticocortical coherence (EEG-EEG, or magneto-encephalography (MEG-MEG)), corticopallidal coherence (EEG-LFP or MEG-LFP), corticomuscular coherence (EEG-EMG or MEG-EMG), pallidopallidal coherence (LFP-LFP), pallidomuscular coherence (LFP-EMG) and intermuscular coherence (EMG-EMG). For all combinations and all dystonia subtypes, an increased low-frequency common drive was found in dystonia patients compared to controls. Strikingly, only writer’s cramp patients present with decreased rather than increased corticocortical coherence in the low frequency band. Furthermore, corticocortical, corticopallidal and intermuscular alpha coherence were decreased by DBS treatment.

Conclusion: There is an increased low-frequency common drive between the cortex, basal ganglia and affected muscles in all dystonia subtypes. Writer’s cramp patients may have different cortical pathology than other dystonia subtypes. For DBS, this “dystonic drive” may serve as a biomarker.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-dystonic-drive-a-systematic-review-on-coherence-analysis-in-dystonia/