Myoclonic seizures are characterized by sudden, brief (<350 milliseconds), shock-like contractions.

The contractions may be:

  • generalized
  • confined to the face and trunk
  • confined to one or more extremities
  • confined to individual muscles or groups of muscles.

Any group of muscles can be involved in the jerk. Myoclonic seizures may be dramatic, causing the patient to fall to the ground, or be quite subtle, resembling tremors. Because of the brevity of the seizures, it is not possible to determine if consciousness is impaired.

Myoclonus may occur as a component of an absence seizure or at the beginning of a generalized tonic-clonic seizure.

Electromyography shows short bursts of synchronized activity, often involving simultaneous activation of agonist and antagonist muscles. The contractions of the muscles are quicker than the contractions with clonic seizures.

On EEG, myoclonic seizures are usually associated with generalized spike-and-wave activity.

Authored By: 
Gregory L. Holmes MD
Authored Date: