Hemiballistic hemi-myoclonus in Subacute Sclerosing Pan encephalitis - A novel observation.

We describe three patients with subacute sclerosing panencephalitis (SSPE) presenting with hemiballistic slow myoclonus, an unusual and rarely reported motor phenotype. Periodic slow myoclonus is a hallmark clinical feature of SSPE and is considered pathognomonic, yet its expression is typically axial or generalized. Hemiballistic presentation of slow myoclonus is distinctly uncommon and has received little attention in the literature. These cases expand the recognized motor repertoire of SSPE and highlight a variant expression of periodic cortical discharges involving asymmetric ballistic recruitment of proximal limb musculature.