myoclonic epilepsy

Last edited 09/2018 and last reviewed 04/2023

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)

Reference:

• NICE (April 2018). Epilepsies: diagnosis and management
• Epilepsy Research UK. What is a myoclonic seizure (Accessed 2/9/18)