Myoclonic seizures are characterized by sudden, brief (<350 milliseconds), shock-like contractions.
The contractions may be:
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.
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.
Reviewed and revised January 2004 by Gregory L. Holmes, MD, Dartmouth Medical School
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