Clinical and neurophysiological characterization of myoclonus in complex regional pain syndrome.

The origin of myoclonus in patients with complex regional pain syndrome (CRPS) is unknown. Eight patients with CRPS related myoclonus were clinically evaluated and studied with intermuscular and corticomuscular coherence analysis. Jerks were present at rest, aggravated during action and were frequently associated with tremulousness or dystonia. Electromyography demonstrated a burst duration ranging from 25 to 240 ms with burst frequencies varying from <1 jerk/s during rest to 20 Hz during action. Coherence studies showed increased intermuscular coherence in 4 patients in the 6 to 12 Hz band, as reported in patients with enhanced physiological tremor. In 2 patients side-to-side coherence was observed, pointing to a central oscillatory drive. Significant coherence entrainment was detected in 5 patients. We conclude that the characteristics of myoclonus in CRPS are different from other forms of myoclonus.