EMG coherence and spectral analysis in cervical dystonia: Discriminative tools to identify dystonic muscles?

Objective: Botulinum toxin injections in the dystonic muscles are the preferred treatment for cervical dystonia (CD), but proper selection of the dystonic muscles remains a challenge. We investigated the use of EMG coherence and autospectral analysis as discriminative tools to identify dystonic muscles in CD patients. Methods: We compared the occurrence of 8-14 Hz autospectral peaks and 4-7 Hz intermuscular coherences between 10 CD patients and 10 healthy controls. Secondly, we compared the muscles with significant 4-7 Hz coherences with the muscles that were selected clinically for botulinum toxin treatment. Results: Autospectral peaks between 8 and 14 Hz were significantly more often absent in the splenius capitis (SPL) muscles of CD patients compared to controls (p < 0.01). Contrary to previous findings, there was no significant difference in the occurrence of 4-7 Hz intermuscular coherences between patients and controls and the diagnostic accuracy of coherence analysis to identify the clinically dystonic muscles was low. Conclusion: Intermuscular EMG coherence analysis cannot reliably discriminate patients from controls. Autospectral changes in the SPL muscles are a more discriminative feature of CD. In patients, coherence analysis does not seem to be a reliable method to identify dystonic muscles. The clinical relevance and the origin of the autospectral changes need further study. (C) 2014 Elsevier B.V. All rights reserved.