Hemifacial spasm and facial myokymia: electrophysiological findings.

In two patients, one with clinical hemifacial spasm (HFS) and one with clinical facial myokymia, the spontaneous electromyographic findings consisted of regular burst activity: each burst composed of high frequency repetitive motor unit potentials. These bursts fired synchronously in multiple ipsilateral facial muscles in both patients and from a contralateral facial muscle in the patient with HFS. In addition, the patient with HFS exhibited crossed evoked responses on the affected side with stimulation of the facial and supraorbital nerves on the unaffected side. It is concluded that the current electrophysiological distinctions between HFS and facial myokymia may be unsupportable and that facial nuclear hyperactivity with activation of bilateral facial nuclear connections plays a role in the pathophysiology of HFS.