Abstract
Movement disorders are rare manifestations of late-onset multiple sclerosis (LOMS). We report a case of a 62 years old man who presented an acute onset of unilateral sustained, irregular, brief contracture in his left-side facial muscles. Clinical, neurophysological and neuroimaging exams allowed a diagnosis of hemifacial spasm (HFS) in MS. Specifically, needle electromyography revealed repetitive motor unit action potentials firing at high frequency discharge (100-150 Hz) in the affected facial muscles., suggesting that demyelinating lesion involved the lower facial motor neurons in the intra-axial exit zone. Blink reflex findings confirmed the efferent demyelinating injury. In literature HFS explicitly associated with MS are described but not as first presentation symptoms of LOMS. A careful neurophysiological evaluation can modify the interpretation of an atypical clinical presentation, allowing to establish the specific anatomical location and extent of injury, and the most appropriate treatment.