OVERVIEW: What every practitioner needs to know
Are you sure your patient has essential myoclonus? What are the typical findings for this disease?
Myoclonus is an involuntary, sudden, shock-like, and brief contraction of a muscle or group of muscles. It can occur repetitively but is usually not rhythmic. Myoclonus can be induced by movement (action myoclonus) or by specific stimuli such as light or sound (reflex myoclonus). Positive myoclonus is when muscle contraction occurs. Negative myoclonus involves muscle relaxation (as seen in asterixis).
Essential myoclonus is considered a form of primary myoclonus, meaning that no proximal cause is identified or that genetic causes are suspected or identified.
Myoclonus can be classified in several ways:
Distribution: focal, multifocal, segmental, or generalized
Etiology: physiologic, primary (idiopathic or hereditary), epileptic, symptomatic (secondary to an underlying disorder), psychogenic
Time of occurrence: at rest, action or reflexive
Primary myoclonus subtypes
Myoclonus is multifocal and arrhythmic
Benign myoclonus of infancy
May mimic infantile spasms
Myoclonus appears daily, usually in clusters
Symptoms diminish and resolve in childhood
Myoclonus dystonia syndrome
Myoclonus may dominate and dystonia may be apparent during activities
What other disease/condition shares some of these symptoms?
The critical element to consider is whether the myoclonus is epileptic in nature or nonepileptic. Types of myoclonus include the following:
Epileptic (without encephalopathy)
Juvenile myoclonic epilepsy
Epileptic (with encephalopathy)
Neuronal ceroid lipofuscinosis
Lafora body disease
Benign myoclonus of infancy
Hereditary essential myoclonus
Myoclonus dystonia syndrome
Hypnic jerks (sleep myoclonus)
What caused this disease to develop at this time?
Onset is typically in the first or second decade of life.
For benign myoclonus of infancy, onset is in the first year of life.
What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?
Electroencephalography is essential to rule out epileptic myoclonus.
Electromyography (EMG) can be considered but is typically not indicated. EMG can help differentiate “positive” myoclonus from “negative” myoclonus.
Laboratory studies should be tailored to findings in the history and physical examination. If the history is consistent with essential myoclonus, no additional testing is needed.
Would imaging studies be helpful? If so, which ones?
Magnetic resonance imaging (MRI) is indicated if there are focal findings on examination or concern for a neurodegenerative process.
Computed tomography of the abdomen and pelvis is indicated if opsoclonus is present with myoclonus to rule out neuroblastoma.
If you are able to confirm that the patient has essential myoclonus, what treatment should be initiated?
For most children with essential myoclonus, reassurance alone is indicated. Treatment with medication is typically reserved for individuals whose myoclonus is significantly impacting their quality of life.
Anticonvulsants: levetiracetam (10 mg/kg/d divided twice daily) valproic acid, clonazepam, zonisamide, piracetam, phenobarbital
Do not use oxcarbazepine, carbamazepine, or phenytoin because they are promyoclonic
What are the adverse effects associated with each treatment option?
Anticonvulsants: sedation, cognitive dulling, rash, weight gain (valproic acid), wieight loss (zonisamide)
What are the possible outcomes of essential myoclonus?
Essential myoclonus is typically benign and nonprogressive.
What causes this condition and how frequent is it?
Overall incidence and prevalence is not known, but it is felt to be rare
Affects men and women equally
Hereditary forms are typically autosomal dominant
Mutations in the epsilon sarcoglycan gene (
SGCE) have been linked to myoclonus dystonia syndrome
How do these pathogens/genes/exposures cause the disease?
Gamma-aminobutyric acid (GABA), glycine, and serotonin are all purported to play a role in the genesis of myoclonus.
What complications might you expect from the disease or treatment of the disease?
Essential myoclonus typically has a benign course.
How can essential myoclonus be prevented?
Essential myoclonus cannot be prevented.
What is the evidence?
Maydell, BV, Berenson, F, Rothner, AD. “Benign myoclonus of early infancy: an imitator of West's syndrome”. J Child Neurol. vol. 16. 2001. pp. 109-12.
Shibasaki, H, Thompson, PD. “Milestones in myoclonus”. Mov Disord. vol. 26. 2011. pp. 1142-8.
Caviness, JN, Truong, DD. “Myoclonus”. Handb Clinc Neurol. vol. 100. 2011. pp. 399-420.
Dijk, JM, Tijssen, MA. “Management of patients with myoclonus: available therapies and the need for an evidence-based approach”. Lancet Neurol. vol. 9. 2010. pp. 1028-36.
Mink, JW, Zinner, SH. “Movement disorders ii: chorea, dystonia, myoclonus and tremor”. Pediatr Rev. vol. 31. 2010. pp. 287-94.
Kaddurah, AK, Holmes, Gl. “Benign neonatal sleep myoclonus: history and semiology”. Pediatr Neurol. vol. 40. 2009. pp. 343-6.
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- OVERVIEW: What every practitioner needs to know
- Are you sure your patient has essential myoclonus? What are the typical findings for this disease?
- What other disease/condition shares some of these symptoms?
- What caused this disease to develop at this time?
- What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?
- Would imaging studies be helpful? If so, which ones?
- If you are able to confirm that the patient has essential myoclonus, what treatment should be initiated?
- What are the adverse effects associated with each treatment option?
- What are the possible outcomes of essential myoclonus?
- What causes this condition and how frequent is it?
- How do these pathogens/genes/exposures cause the disease?
- What complications might you expect from the disease or treatment of the disease?
- How can essential myoclonus be prevented?
- What is the evidence?