Myoclonus: what it is, causes, myoclonic seizures and when to seek help

Myoclonus is a sudden, brief, involuntary muscle jerk. Epilepsy Action explains that when this is part of epilepsy it is called a myoclonic seizure, and that these are sometimes called myoclonus or myoclonic jerks. It says they are quick, sudden muscle movements that can affect part of the body or all of it, such as the upper body, legs or arms.

In people with epilepsy, Epilepsy Action says myoclonic seizures have a generalised onset, which means both sides of the brain are affected from the start. The jerking can be very mild, like a twitch, or very forceful. If a jerk is strong you may throw something you are holding, or fall over. They can happen when you are awake or asleep, though research suggests they are more likely when you are awake.

The sources reviewed here, from UK epilepsy charities, focus on the epilepsy-related form. Myoclonus can have other causes that a neurologist would consider, so a medical assessment is important after any new, repeated jerks.

Epilepsy Action quotes people who describe a hand that suddenly goes limp and drops whatever it holds, or a feeling like an electric shock without the pain, and anxiety about when they will happen. The jerks last for less than a second and some people have them in clusters.

After a single seizure, you can usually get back to what you were doing straight away. Some people feel confused or tired afterwards, or if there is a cluster they may want to lie down. They can cause injuries or accidents, such as spilling hot drinks, particularly if someone is holding something hot or sharp.

Epilepsy Action says myoclonic seizures can happen in many types of epilepsy. They are often a feature of some childhood epilepsy syndromes, but not always. It lists juvenile myoclonic epilepsy (JME), epilepsy with myoclonic-atonic seizures (Doose syndrome), myoclonic epilepsy in infancy, Lennox-Gastaut syndrome and epilepsy with myoclonic absences as examples. Adults and older adults can sometimes develop myoclonic seizures, for example after a stroke or another illness or injury.

Seizure triggers listed by Epilepsy Action include lack of sleep, alcohol and stress. Epilepsy Action says over one third of people with JME are photosensitive, meaning flickering or flashing lights can trigger seizures, particularly if they are tired.

Epilepsy Action describes JME as one of the most common epilepsy syndromes starting in children and young people, with around 1 in 10 people with epilepsy having it. It usually starts between 12 and 18 years, is slightly more common in girls, and about one third of children who develop it may have a family member with epilepsy.

All people with JME have myoclonic seizures. About 9 in 10 also have tonic-clonic seizures, often following a cluster of myoclonic jerks, and about one third have absence seizures. People with JME are much more likely to have seizures when they do not get enough sleep, and seizures often happen soon after waking.

It says myoclonic seizures can be easily missed and mistaken for clumsiness or a normal part of waking up, and that people often seek a diagnosis only after a tonic-clonic seizure.

Epilepsy Action says that if you have a first myoclonic seizure you may not need immediate medical help unless you injure yourself, but you should make an urgent appointment to see your GP, who can decide whether any tests or a referral to a specialist are needed.

For JME, it says children and teenagers should see a paediatrician after a seizure and adults a specialist in epilepsy. The specialist will often recognise JME from the description, asking about sudden jerks after waking. An EEG (electroencephalogram) of brain electrical activity can help confirm the diagnosis, sometimes after a night of poor sleep and with flashing-light testing. It says brain scans and blood tests are not usually needed to diagnose JME.

Epilepsy Action says the main treatment for myoclonic seizures is epilepsy medicine, and points to NICE guidelines for details. For JME, it says most people have seizures fully controlled with epilepsy medicines. Which medicine is suitable depends on the person, so this is a decision for a specialist.

Self-help measures from Epilepsy Action include learning your triggers with a seizure diary, getting enough sleep, being careful with hot or sharp items and using lids on hot drinks, and following safety advice. It also notes there are specific DVLA rules for driving with epilepsy depending on the type and timing of seizures.

Not every jerk is a seizure. The NHS says tics are fast, repetitive muscle movements that result in sudden and difficult-to-control body jolts or sounds, fairly common in childhood and first appearing at around 5 years of age. Tics often start with an unpleasant sensation that builds up until relieved by the tic, can sometimes be partly suppressed, and tend to get worse if they are talked about or focused on.

Epilepsy Action says that in very rare cases myoclonic seizures can happen one after another for a long time or turn into a prolonged tonic-clonic seizure, called status epilepticus, which is a medical emergency. It is status epilepticus if someone has myoclonic seizures clustering for over 30 minutes, or a continuing tonic-clonic seizure for longer than 5 minutes. It says to call an ambulance if this happens or if you are worried.

See a GP urgently after a first seizure, and soon if jerks become more frequent, you injure yourself, or you notice new symptoms such as weakness, confusion or loss of awareness.

On the NHS, a GP can refer you to a paediatrician, neurologist or epilepsy specialist for an EEG and treatment. Some people choose a private neurology consultation for a faster EEG. Medicines and follow-up are then shared with your GP. Epilepsy Action runs a helpline for information and support.