Myoclonus

Overview

Myoclonus refers to a quick jerking movement that you can't stop from happening. Hiccups and the sudden jerks or "sleep starts" that you may feel just before falling asleep are forms of myoclonus. These movements occur in otherwise healthy people and usually aren't serious.

Other forms of myoclonus may be due to a nervous system condition, such as epilepsy. Jerking movements also can result from a metabolic condition or a reaction to a medicine.

Treating the condition that causes myoclonus can help manage symptoms, but sometimes the cause isn't known. When this happens, the goal of treatment is to reduce the effects of myoclonus on quality of life.

Types

Myoclonus can appear in different patterns, and specialists group these patterns into types to help describe what the jerking movements look like and what may be causing them. An updated classification system gives a clearer way to organize these types and guide care.

Newer ways of classifying myoclonus

Experts recently updated how myoclonus is grouped and described. This helps care teams talk about the condition in a clearer, more consistent way and gives a better framework for choosing tests and treatments.

Why an update was needed

Older labels such as essential, epileptic or symptomatic myoclonus are still helpful, but they don't fully capture the many different ways myoclonus can appear or what causes it. As testing methods have improved, specialists needed a system that reflects what is now known.

What's new

The updated approach looks at myoclonus from two angles:

1. What the jerking movements look like. This includes:

   • Where they happen on the body.
   • What brings them on, such as movement, sound, touch or rest.
   • How strong or frequent they are.
   • What simple nerve and muscle tests show.

   This helps the care team understand how the jerks are being generated in the nervous system.

2. What is causing the jerking movements. This includes:

   • Genetic conditions.
   • Metabolic or chemical imbalances.
   • Infections or inflammation.
   • Structural changes in the brain or spinal cord.

Looking at both the features and the possible causes gives a clearer overall picture.

How this helps in care

This system is already being used by neurologists and movement disorder specialists. It supports more-accurate diagnosis and helps guide next steps, such as which tests may be most helpful and which treatments may be appropriate.

You may not hear the technical terms during a visit with your healthcare professional, but the updated system helps the care team describe myoclonus in a more organized and consistent way behind the scenes.

Symptoms

People with myoclonus often describe their symptoms as jerks, shakes or spasms that are:

• Sudden.
• Brief.
• Not voluntary.
• Shocklike.
• Variable in how often they happen and how serious they are.
• In one part of the body or all over the body.
• Sometimes serious enough that they affect how people eat, speak or walk.

When to see a doctor

If your myoclonus symptoms become frequent and lasting, talk to your healthcare professional about a diagnosis and treatment options.

Causes

Myoclonus can happen for many different reasons. Some cause-related categories can help describe why the jerking movements occur and guide treatment options.

Physiological myoclonus

This type of myoclonus occurs in healthy people and rarely needs treatment. Examples include:

• Hiccups.
• Sleep starts.
• Shakes or spasms due to anxiety or exercise.
• Infant muscle twitching during sleep or after a feeding.

Essential myoclonus

Essential myoclonus occurs on its own, usually without other symptoms and without being related to an illness. The cause is often not known. Sometimes essential myoclonus is passed down in families, known as a genetic trait.

Epileptic myoclonus

This type of myoclonus occurs as part of a brain condition that causes seizures, known as epilepsy.

Symptomatic myoclonus

Symptomatic myoclonus results from a medical condition. It is sometimes called secondary myoclonus. Examples include:

• Head or spinal cord injury.
• Infection, including coronavirus disease 2019 (COVID-19).
• Kidney or liver failure.
• Lipid storage disease.
• Medicine reaction or chemical poisoning.
• Long-term reduction in oxygen levels.
• Autoimmune inflammatory conditions or metabolic conditions.

Nervous system conditions that result in secondary myoclonus include:

• Stroke.
• Brain tumor.
• Huntington's disease.
• Creutzfeldt-Jakob disease.
• Alzheimer's disease, frontotemporal dementia or Lewy body dementia.
• Parkinson's disease.
• Corticobasal degeneration.
• Multiple system atrophy.

Risk factors

Risk of myoclonus is higher in people who have nervous system conditions. This includes epilepsy, Parkinson's disease, Huntington's disease and others. It also can occur in people with other conditions, such as an infection, a brain tumor or a spinal cord injury. Essential myoclonus can run in families, so your risk is higher if a family member has it.