Myoclonus of peripheral origin: two case reports

Abstract

The concept of peripheral myoclonus is not yet fully accepted by the medical community because of the difficulty in establishing a cause-and-effect relationship between trauma and subsequent movement disorders. Here, we report two cases of patients suffering from peripheral myoclonus after nerve injury. The first patient experienced myoclonus of the 4th dorsal interosseous muscle several days after trauma to the elbow. The second patient presented myoclonus of the arm stump (combined with phantom-limb pain) 1 year after amputation. In both cases, central nervous system function (spine and brain imaging, somesthetic evoked potentials, EEG back-averaging) was normal. For the second patient, local infiltration of xylocaine and botulinum toxin into the stump scar rapidly stopped myoclonus and pain. Nerve injury induces ephaptic transmission and ectopic excitation. The physiopathological mechanisms of this type of myoclonus involve a peripheral generator that induces central (spinal) generator activity.