Myoclonus is a rapid, involuntary muscle jerk. Examples of myoclonus in healthy individuals include the twitching of an arm or leg when someone is falling asleep, hiccups, and a sudden jerk or twitch when someone is startled. Other types of myoclonus may occur as a result of a health condition. When muscle jerks happen frequently or affect more than one area of the body, they can make it challenging to carry out basic activities such as talking, eating, and walking.
Individuals who experience myoclonus describe their symptoms as shakes, jerks, or spasms that are involuntary, sudden, shock-like, and brief. The jerks may vary in intensity and frequency. Myoclonus can be localized to one area or occur over the entire body.
Many factors can lead to myoclonus, and doctors categorize them based on the underlying cause. Healthy individuals experience physiological myoclonus, and this type rarely needs treatment. Examples of physiological myoclonus include spasms or shakes while feeling anxious or exercising, hiccups, and twitching or jerking while falling asleep. It is also normal for infants to twitch after being fed or during sleep.
Essential myoclonus happens on its own without an underlying illness and generally does not worsen over time or impair cognitive function. The cause is typically idiopathic (unknown). In some cases, this type of myoclonus is hereditary. In 30 to 50% of hereditary cases, a mutation in the epsilon-sarcoglycan gene is responsible. The mutation is much more likely to lead to essential myoclonus if the person inherited the gene from their father than from their mother.
Epileptic myoclonus occurs in individuals with epileptic disorders and can occur in both primary generalized epilepsy syndromes -- such as Jeavon's syndrome and juvenile myoclonic epilepsy (JME) -- and secondary (symptomatic) generalized epilepsy syndromes such as primary myoclonic epilepsy (PME). The latter causes individuals to experience myoclonus, seizures, and difficulty speaking or walking. PME usually begins during childhood or adolescence. The rare conditions classified as PME are often progressive and can be fatal.
Myoclonus can occur as a result of numerous medical conditions, including a head or spinal cord injury, metabolic disease, liver or kidney failure, autoimmune inflammatory disease, drug or chemical poisoning, infection, lipid storage disease, and reactions to medication. Nervous system disorders can also result in secondary myoclonus. Stroke, Creutzfeldt-Jakob disease, Lewy body dementia, Parkinson's disease, Alzheimer's disease, frontotemporal dementia, Huntington's disease, corticobasal degeneration, brain tumor, multiple sclerosis, stiff-person syndrome, and multiple system atrophy can all cause secondary myoclonus.
A doctor will not only want to diagnose myoclonus but also determine what the underlying cause of the muscle jerks to create an appropriate treatment plan. He or she may order several tests to help determine the cause:
There are no specific medications for myoclonus, but doctors commonly use medications prescribed for other conditions that cause muscle jerking. Tranquilizers can ease myoclonus, but they also cause drowsiness and loss of coordination. Anticonvulsants for seizure disorders may effectively relieve muscle jerks but have side effects such as sleepiness and nausea.
Injections may effectively treat myoclonus, especially if the muscle jerks only occur in one area of the body. Botulinum toxins inhibit the release of a chemical messenger that causes muscles to contract. The injections have several possible side effects, including pain, bruising, or swelling at the injection site, headache, flu-like symptoms, dry eyes or excessive tearing, and fever. As with any treatment, doctor and patient must weigh the benefits against the detriments.
A lack of sleep may increase seizure activity in some individuals, so those prone to this symptom should make sure they get adequate sleep each night. Low blood sugar can also trigger seizures, making it important that people with epilepsy eat regularly. Flashing lights are also well-known seizure triggers people with these conditions should avoid.
Surgery may benefit those whose muscle jerks are caused by a tumor or lesion in the brain or spinal cord. Myoclonus that affects the face or ears may also be good candidates for surgery. Some people with myoclonus and other movement disorders undergo deep brain stimulation (DBS), but further research needs to be done to determine the effectiveness of this treatment.
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