Motor seizure Myoclonic seizure 2020-03-16T13:28:08Z This term describes the initial semiology of the seizure without specifying whether the onset is focal or generalized. Thus it can be used for coding myoclonic seizures when the onset is not known. A myoclonic seizure is a type of motor seizure characterized by sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus.