Myoclonic seizures are brief, shock-like jerks of a muscle or a group of muscles
- "Myo" means muscle and "clonus" (KLOH-nus) means rapidly alternating contraction and relaxation - jerking or twitching - of a muscle
- myoclonic seizures
- sudden brief (< 100 ms) and almost shock-like involuntary single or multiple jerks due to abnormal excessive or synchronous neuronal activity and associated with polyspikes on EEG (1)
- usually last no more than a few seconds
- may occur singularly but sometimes many will occur within a short time
- note that people without epilepsy can experience myoclonus in hiccups or in a sudden jerk that may wake you up as you're just falling asleep - these are normal (2)
In epilepsy, myoclonic seizures usually cause abnormal movements on both sides of the body at the same time. They occur in a variety of epilepsy syndromes that have different characteristics:
Juvenile myoclonic epilepsy:
- has an age of onset of 6-22 (peak 10-16 years)
- accounts for 4-12 % of childhood epilepsy
- seizures usually involve the neck, shoulders, and upper arms
- generally the seizure occurs in the first hour after waking
- epileptogeneic photosensitivity occurs in at least half of patients with JME
- in most cases, these seizures can be well controlled with medication but it must be continued throughout life
Lennox-Gastaut syndrome:
- is an uncommon syndrome that usually includes other types of seizures as well
- begins in early childhood
- myoclonic seizures usually involve the neck, shoulders, upper arms, and often the face. They may be quite strong and are difficult to control.
Progressive myoclonic epilepsy:
- the rare syndromes in this category feature a combination of myoclonic seizures and tonic-clonic seizures
- treatment is usually not successful for very long, as the patient deteriorates over time
Notes:
- if the person has myoclonic seizures or is suspected of having juvenile myoclonic epilepsy (JME), be aware that lamotrigine may exacerbate myoclonic seizures (1)
- carbamazepine and oxcarbazepine have the risk of exacerbating myoclonic or absence seizures (1)
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