Cortical myoclonus mainly affects the distal upper limbs and face, which reflects the largest cortical representations of these body areas. It is often focal, but may be multifocal, bilateral or generalized, as a consequence of intracortical and transcallosal spreading of abnormal activity. It typically occurs on voluntary action and may affect speech and gait. Cortical myoclonic jerks are stimulus sensitive, typically to touch, but sensitivity to visual stimuli is also described. Most patients with cortical myoclonus have both positive myoclonus and NM, occurring either independently or together as a complex of the two kinds of myoclonus. If cortical myoclonus is prolonged and lasts for hours, days or weeks, it is called epilepsia partials continua and is considered to be a rare form of focal epileptic status. Focal cortical myoclonus almost always points to an underlining lesion of the sensori-motor cortex, which produces hyperexcitability (e.g. vascular, inflammatory or neoplastic). [from
HPO]