Segmental facial myoclonus in Moebius syndrome

Moebius syndrome is characterized by sixth and seventh nerve palsy and is u sually the result of bilateral hypoplasia or aplasia of the respective brai n stem nuclei. There have been no reports of involuntary facial movements a ssociated with this malformative complex. We report on a 6-year-old boy aff ected by Moebius syndrome with asymmetric involvement and segmental facial myoclonus with onset at age 2 years, affecting the side with partially cons erved motility. Clinical presentation included congenital peripheral palsy of the right seventh cranial nerve and left-sided rhythmic rising of the up per lip and eyebrow. Surface-electromyography (EMG) of the left levator lab ii and frontalis muscles showed rhythmic bursting (duration: 150-450 ms; fr equency: 1-3 Hz). Electroencephalographic (EEG)-polygraphic recordings and burst-locked EEG averaging failed to show any consistent EEG activity prece ding the EMG bursts. Study of the blink reflex, somatosensory and motor-evo ked potentials showed findings consistent with pontine pathology. Segmental facial myoclonus, although extremely rare in children, must be differentia ted from several other paroxysmal motor manifestations associated with stru ctural lesions involving the brain stem.