Enhanced broad-band intermuscular coherence in myoclonus: a targeted characterization study

To describe the occurrence of enhanced broad-band intermuscular coherence (eIMC) in cortical myoclonus (CM) and to examine whether this pattern reflects a physiological synchronization mechanism or an alteration associated with CM.

eIMC was examined in 19 patients with CM, 19 essential tremor (ET), and 39 healthy control (HC) during three standardized postures. Signal quality was assessed to exclude noise or artifacts as underlying causes. We analyzed the prevalence of eIMC across groups and postures and compared coherence values in the 4-12 Hz, 12-30 Hz, and 30-100 Hz frequency bands.

eIMC occurred in all groups and was more frequently observed during conditions involving stronger voluntary muscle activation. Its higher prevalence in CM suggests that the underlying physiological mechanism may be more strongly expressed in CM. Median IMC values in CM exceeded those in ET and HC, especially in the 4-12 Hz and 12-30 Hz frequency bands.

eIMC appears to be a physiological feature of motor control that can be detected across CM, ET, and HC. Its higher prevalence in CM may reflect pathological irregular, synchronous myoclonic discharges or amplification of the synchronization mechanism in the context of cortical hyperexcitability.

eIMC may serve as a supportive marker in the evaluation of CM diagnosis.