Myoclonic Seizure Characteristics

Definition and Diagnosis

Myoclonic seizures are characterized by sudden, brief, involuntary jerks lasting only a fraction of a second, with preserved consciousness during the event, and can be symmetrical/synchronous or asymmetrical/asynchronous 1
The American Heart Association and European medical guidelines imply that myoclonic seizures involve brief, shock-like muscle contractions that can affect specific body parts, in a conscious patient 1

Tonic seizures involve sustained, forceful muscle contractions rather than brief jerks, cause forceful extension of extremities, and can cause the patient to lose balance, typically associated with loss of consciousness 2, 3
Clonic seizures consist of massive, synchronous, rhythmic jerks of arms and/or legs, involve repetitive rhythmic contractions, and usually many movements rather than single brief jerks, most commonly associated with loss of consciousness 2, 3, 4, 5

The term "myoclonus" describes individual abrupt involuntary movements, and "clonic" is restricted to epilepsy with rhythmic, massive jerks, myoclonic movements can occur with preserved consciousness 4, 5, 6
Myoclonic seizures can be distinguished from syncope-related myoclonus, as syncopal movements are typically asynchronous, limited in scope, and occur after loss of consciousness, whereas epileptic myoclonic seizures begin at or shortly after onset of any loss of consciousness, but can occur while fully conscious 1, 2, 3