Myoclonus

"Myoclonus" is a term used to describe sudden, often brief, involuntary spasms or twitching of a muscle or group of muscles. Myoclonus is not a disease; roughly 72% of the time it is considered a clinical sign of an underlying condition or a reaction to medication.

This article looks at myoclonus symptoms, its causes, treatment, and when to seek medical care.

A young woman rubbing her eye after an eye spasm (myoclonus).

AndreyPopov / Getty Images

What Is Myoclonus and When Does It Occur?

Myoclonus is sudden, involuntary spasms of a single muscle or group of muscles. It is not common and affects approximately 8.6 individuals per 100,000.

It can begin in childhood or adulthood, and symptoms can range from mild to extreme. The prevalence of myoclonus tends to increase after 50 years of age.

Symptoms of Myoclonus

An individual with myoclonus will usually experience one or both of the following symptoms:

  • Positive myoclonus, which is a sudden muscle contraction or tightening that might be described as feeling a muscle twitch or spasm
  • Negative myoclonus, also called asterixis, which occurs when a muscle involuntary relaxes, resulting in a sudden inability to move a limb

Common Myoclonus Jerking Motions

The jerking motions of myoclonus have several common patterns. They can:

  • Occur alone or sequentially
  • Have a pattern or be inconsistent
  • Occur infrequently or many times in a row
  • Spontaneously occur in an otherwise healthy individual when there is a strong response to an external event or in an attempt to make a movement

Types of Myoclonus

Myoclonus is generally divided into these two categories:

Physiologic myoclonus: This type of myoclonus is characterized by a quick muscle twitch followed by relaxation. Examples include hiccups or "sleep starts," which are involuntary muscle jerks sometimes experienced in the beginning stage of sleep.

Pathologic myoclonus: This form usually involves persistent contractions, similar to an electric shock, in a group of muscles and is often more widespread. Extreme cases might impact movement and cause eating, talking, or walking difficulties.

What Is Myoclonus Caused By?

Of the two categories of myoclonus, physiologic myoclonus is often random, causing little or no difficulties, and rarely requires medical treatment.

Pathologic myoclonus often indicates an underlying neurologic disorder in the brain or nervous system, a symptom of non-neurological medical conditions, or a medication reaction. Some of the underlying conditions with myoclonus as a symptom include:

Neurotransmitters and Myoclonus

Neurotransmitter receptor abnormalities can cause myoclonus as it affects messaging between nerve cells. Some of the neurotransmitter receptor abnormalities that contribute to myoclonus include the following:

  • Serotonin is critical for regulating mood, thought processes, memory, and other physiologic processes.
  • Gamma-aminobutyric acid (GABA) regulates motor control.
  • Glycine is necessary to regulate the spinal cord's motor and sensory functions.
  • Opioid receptors are involved with different functions related to pain, pain relief, and depression.

How to Treat Myolconus

Physiologic myoclonus can affect anyone, is almost always benign, and requires no medical treatment or follow-up.

For pathologic myoclonus, identifying the underlying cause is necessary for a healthcare provider to determine the optimal course of treatment.

Some of the options available to treat myoclonus include:

  • Medications: The most common drug used to alleviate myoclonus symptoms is Klonopin (clonazepam). Although helpful for relaxing the muscles and decreasing or eliminating myoclonus symptoms, individuals using clonazepam often have to increase dosing over time, which can cause other side effects like drowsiness. When combined with other medications, such as epilepsy medications like valproate or Keppra (levetiracetam), myoclonus symptoms can often subside without side effects.
  • Hormone therapy: This has been shown to decrease symptoms of specific myoclonus subtypes. For example, the adrenocorticotropic hormone (ACTH) can help treat irregular rapid eye movements known as opsoclonus myoclonus.
  • 5-hydroxytryptophan (5-HTP): For some subtypes of myoclonus in which the underlying issue is a neurotransmitter receptor abnormality, 5-HTP can alleviate myoclonus symptoms. The chemical 5-HTP is a building block for serotonin and can correct neurotransmitter receptor abnormalities.
  • Botulinum toxin (Botox) injections: For peripheral myoclonus (spasms that originate from nerves outside the brain or spinal cord), botulinum toxin injections can paralyze the spasming muscles. Since these injections only offer a temporary effect, you may need repeated injections every few months if symptoms reappear.
  • Stopping or changing medication causing myoclonus: If myoclonus is not due to an underlying condition or injury, the next most common cause is a medication of some kind. A healthcare provider should be able to identify the medication and stop or change the dosing to alleviate myoclonus symptoms.

Are There Tests to Diagnose Myoclonus?

Your healthcare provider will complete a thorough medical history and physical examination. During the physical exam, one specific assessment will likely include evaluating your neurological system by checking your reflexes, motor strength, balance, sensory function, and coordination.

Depending on your history and physical examination results, your healthcare provider might order laboratory testing or imaging studies to further determine the underlying cause of myoclonus.

When to See a Healthcare Provider

It is not usually necessary to see a healthcare provider for myoclonus episodes that are brief, infrequent, and nonrepetitive. However, you should seek medical care if any of the following are present:

  • Episodes that are long-lasting or increasing in length
  • Frequent episodes
  • Episodes that follow a pattern
  • Symptoms are impacting your ability to eat, talk, sleep, or walk freely

Summary

Myoclonus is rare and often a symptom of an underlying disease or injury. Roughly 72% of myoclonus symptoms are due to an underlying condition or injury. Brief, intermittent episodes of myoclonus, like hiccups, do not generally require medical treatment and should not be a source of concern.

However, if myoclonus symptoms become more consistent and are constant, it can be helpful to see a healthcare provider. Although myoclonus is not necessarily curable, symptoms can often be treated to provide enhanced quality of life.

A Word From Verywell

Experiencing myoclonus can be overwhelming and upsetting, especially if there are indications of a disease or injury causing your symptoms. Understanding what myoclonus is and different methods to treat it can help you work with your healthcare provider to achieve a better quality of life with fewer symptoms.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institute of Neurological Disorders and Stroke. Myoclonus fact sheet.

  2. National Library of Medicine. Myoclonus.

  3. Genetic and Rare Disorders Information Center. Myoclonus-dystonia.

  4. National Institute of Neurologic Disorders and Stroke. Opsoclonus myoclonus.

By Pamela Assid, DNP, RN
Pamela Assid, DNP, RN, is a board-certified nursing specialist with over 25 years of expertise in emergency, pediatric, and leadership roles.