[Synchronized hemifacial spasm induced by sound stimulation].

A 42-year-old woman whose hemifacial spasm develops not only involuntarily but also synchronously to the sound stimulation to the left ear is presented. She had about 10 years history of left hemifacial spasm which occurred only involuntarily, and she was treated successfully by microvascular decompression method on June 1982. She had been uneventful and free from facial spasm until around January 1983, about 7 months after the first surgery, when her hemifacial spasm recurred and interestingly enough, this spasm started to occur not only involuntary but also synchronously to stimulation of the sound. On her electromyography (EMG) of the face, high amplitude discharge were noted sporadically during her facial muscle twitching, but more constant and regular high amplitude discharge on EMG were also evoked invariably and synchronously with the sound stimulation which was induced by 90 dB click sound and once this sound stimulation discontinued her facial muscle twitching ceased and abnormal discharge of EMG which appeared with sound stimulation disappeared instantly. On March 18, 1983, her left posterior fossa was explored and another angled artery was found compressing the facial nerve just at the root entry zone, more proximally than the previous site where the nerve was found compressed and decompressed at the first surgery. After complete replacement of this offending artery from the nerve, her facial spasm disappeared completely and was never evoked by the sound stimulation. Her postoperative EMG revealed no abnormal discharges at all after the sound stimulation by click sound in the ear.(ABSTRACT TRUNCATED AT 250 WORDS)