Pathophysiology of Myoclonic Seizures

Introduction and Definitions

Myoclonic seizures (MS) are characterized by sudden, brief (<350 ms), shock-like contractions that vary in their distribution and intensity of manifestations (Leppik 2003). They may be generalized or confined to the face and trunk, or to extremities, or individual muscles or groups of muscles. MS can occur unilaterally or bilaterally, and if bilaterally, symmetrically or asymmetrically. They may also be rhythmic or arrhythmic, and, in terms of amplitude, they can be small (e.g., no joint movement) or massive contractions (e.g., movement of extremities, trunk, and/or head) (Video 1, 2)(Leppik 2003; Browne and Holmes 2004). Myoclonic jerks may originate in the form of brief electromyographic (EMG) burst (i.e., positive myoclonus) or, more rarely, from brief interruptions of EMG activity (i.e., negative myoclonus) (Genton et al. 2005; Guerrini et al. 2005). MS may be very subtle or extremely dramatic and can be present in several different epilepsy syndromes,...