Myoclonus

By: Tina Shahian, PhD

Last Updated: Mar 1, 2019

Overview

Myoclonus refers to a sudden, brief, and involuntary muscle jerk. Healthy people can have myoclonus in the form of hiccups and “sleep starts”, which are the sudden jerky sensations that can occur as people fall asleep. Myoclonus can also occur due to underlying neurological disorders such as epilepsy, metabolic conditions, or adverse reactions to medications. Importantly, myoclonus is a symptom, not a diagnosis of a disease.

Sudden positive muscle contractions are called positive myoclonus, whereas muscle relaxation is called negative myoclonus. Myoclonus can vary in frequency, and can occur alone or in a sequence. There are several underlying conditions that can give rise to myoclonus symptoms. Doctors aim to isolate and treat the underlying cause of myoclonus symptoms. When the underlying cause cannot be treated or cured, the aim of treatment is to alleviate severe myoclonus.

There are many types of myoclonus and each type may be caused by several underlying problems. Doctors try to identify the underlying cause of the myoclonus, which helps to determine the most appropriate and effective treatment.

• Physiological myoclonus occurs in healthy people and rarely requires medical treatment. Examples include hiccups, sleep starts, muscle twitching in infants (especially during sleep), and brief shakes or spasms induced by anxiety or exercise.
• Epileptic myoclonus occurs as part of an underlying epileptic disorder. Subtypes of epilepsy-induced myoclonus include cortical reflex myoclonus, progressive myoclonus epilepsy, and reticular reflex myoclonus. Each subtype refers to a form of epilepsy that affects different brain regions.
• Sleep myoclonus occurs just as a person is about to fall asleep. While this symptom can occur in healthy people with no impact on quality of life, sleep myoclonus can also present as restless legs syndrome, which requires medical treatment.
• Essential myoclonus occurs in the absence of any nervous system disorder. It can occur with or without any family history and usually remains stable without changes in severity over time.
• Palatal myoclonus is characterized by a rhythmic contraction of the soft palate (rear of the roof of the mouth). These rapid contractions can persist even during sleep. The condition can also lead to a “clicking” sound in the ear. This form of myoclonus can cause minor discomfort or severe pain.

Causes

Secondary or symptomatic myoclonus can occur due to a variety of underlying medical conditions. Examples include:

• Head or spinal cord injuries
• Infections
• Kidney/liver failure
• Lipid storage disease
• Chemical or drug poisoning
• Prolonged oxygen deprivation
• Adverse reaction to medication
• Autoimmune inflammation
• Metabolic diseases.

Secondary myoclonus can also occur due to neurological disorders such as:

• Stroke
• Brain tumor
• Huntington’s disease
• Alzheimer’s disease
• Parkinson’s disease and Lewy body dementia
• Corticobasal degeneration
• Frontotemporal dementia
• Multiple system atrophy
• Creutzfeldt-Jakob disease.

Symptoms

Myoclonus is often described as jerks, shakes and spasms that are involuntary, sudden, brief, and shock-like. The symptoms can vary in intensity and frequency, and may be localized to one body part or be present all over the body. Severe myoclonus can interfere with a person’s ability to walk, talk or eat.

Diagnosis and Treatment

A doctor will typically review a patient’s medical history and perform a physical examination to first diagnose myoclonus. Several tests can be recommended to isolate the underlying cause of the myoclonus. These tests include:

• Electroencephalography (EEG): An EEG records the brain’s electrical activity. Small electrodes are attached to the patient’s head and the patient is asked to breathe deeply and look at bright lights or listen to sounds. The EEG can help determine the exact origin of the myoclonus in the brain.
• Electromyography (EMG): An EMG can establish the pattern of the myoclonus by measuring the affected muscles’ electrical discharge. Surface electrodes are placed on the affected muscles and an instrument records the electrical activity as the patient contracts the muscle. The EMG signals can help determine the pattern and origin of the myoclonus.
• Magnetic resonance imaging (MRI): An MRI is used to identify tumors or structural abnormalities in the brain and spinal cord, which may be the underlying cause of myoclonus symptoms. Patients are placed inside an MRI scanning machine, which uses magnetic field and radio waves to produce detailed images of the brain and spinal cord.
• Laboratory tests: Doctors may suggest a variety of blood, urine, or genetic tests to identify the underlying cause of myoclonus. These tests may help identify diabetes; kidney or liver disease; drugs or toxins; metabolic disorders; and autoimmune disorders.

The most effective way to treat myoclonus is by identifying and treating the underlying cause. When the cause cannot be identified and treated, the goal is to ease the myoclonus symptoms. Medications include:

• Tranquilizers: Tranquilizers like clonazepam (Klonopin®) are commonly used to alleviate myoclonus symptoms.
• Anticonvulsants: Anticonvulsants like levetiracetam (Keppra®), valproic acid (Depakene®) and primidone (Mysoline®) are typically used to control epileptic seizures. As such, they can also be effective at reducing myoclonus symptoms.
• Botox: OnabotulinumtoxinA, or Botox, can help treat myoclonus, especially in cases where a discrete body part is affected. This medication works by blocking the chemical messengers that trigger muscle contractions.

Doctors may recommend surgery in cases where myoclonus symptoms are caused by tumors or lesions in the brain or spinal cord. Surgery may also be appropriate for patients who have myoclonus in the face or ear. Deep brain stimulation is currently under investigation as a potential treatment option for myoclonus.

Sources

• “Myoclonus fact sheet”. National Institute of Neurological Disorders and Stroke. Retrieved July 2016. http://www.ninds.nih.gov/disorders/myoclonus/detail_myoclonus.htm
• “Myoclonus”. Mayo Clinic. Retrieved July 2016. http://www.mayoclinic.org/diseases-conditions/myoclonus/home/ovc-20166171