Myoclonus (Muscle Twitch)

Myoclonus is a brief, sudden muscle movement (like a twitch, jerk or spasm). It happens when muscles incorrectly activate. It usually lasts just a fraction of a second. Myoclonus (pronounced “my-OCK-lon-us”) can affect a single muscle or a group of them.

There are two main ways it happens:

• Positive myoclonus: Muscles contract or flex suddenly.
• Negative myoclonus: Muscles relax suddenly. (The technical term for this is “asterixis.” Experts often describe it as a “hand-flapping tremor.”)

These muscle movements:

• Are sudden and brief
• Are out of your control (involuntary)
• Feel shock-like
• Can range in intensity and frequency
• Can sometimes be severe enough to affect how you eat, speak or walk

Myoclonus has several possible causes. It may be harmless and be the only symptom you have. It can also be a sign of several medical conditions, some of which are serious.

What are the most common causes of myoclonus?

Myoclonus can happen for many reasons. Experts divide it into four main categories.

Typical forms of myoclonus

Some muscle twitches happen for normal reasons. Experts call this physiological myoclonus. Examples include:

• Sleep myoclonus (hypnic jerks): These are sudden, sharp muscle movements that happen as you fall asleep or wake up.
• Hiccups: These are muscle contractions that affect your diaphragm. They’re normal unless they last a couple of days or more.
• Startle reflexes: These are jump-like movements you can’t control when you’re surprised or scared.

Epileptic myoclonus

Myoclonus can happen as a result of abnormal electrical signals in your brain (also called myoclonic seizures). This type of seizure can occur in different forms of epilepsy, such as Lennox-Gastaut syndrome or juvenile myoclonic epilepsy.

Secondary myoclonus

When myoclonus is a symptom of another condition, experts call this secondary myoclonus. Several conditions can cause it, including:

• Autoimmune inflammatory conditions, like autoimmune thyroiditis
• Brain damage, like from a stroke or a lack of oxygen to your brain
• Degenerative brain diseases, like Alzheimer’s disease and Lewy body dementia
• Electrolyte imbalances
• Genetic disorders, like Krabbe disease and Wilson disease
• Infections, like herpes simplex virus or Lyme disease
• Kidney and liver disease
• Nerve and spinal cord injuries
• Substances, like alcohol, cocaine and inhalants
• Prescribed medications, like antidepressants, blood pressure medicines, antibiotics and others
• Poisons and toxins, like lead, mercury and insecticides
• Vitamin deficiencies

Essential myoclonus

Essential myoclonus happens by itself without an underlying condition or other symptoms. It isn’t harmful and usually doesn’t get worse over time. It can have an unknown cause or be genetic (runs in biological families).

Other forms

Many other forms of myoclonus happen only in certain age groups or in very specific ways, including:

• Benign neonatal sleep myoclonus (BNSM): This can affect newborn babies while they sleep. It’s harmless. About 95% of cases go away by 6 months of age.
• Middle ear myoclonus: This affects the tensor tympani, a muscle in your ear. It can cause repetitive clicking, cracking or thumping sounds. It’s disruptive but not dangerous.
• Opsoclonus-myoclonus syndrome (OMS): This causes uncontrollable movements of your eye muscles and myoclonus at the same time. It has several causes.
• Palatal myoclonus: This affects your soft palate, which is at the upper back of your mouth. It can cause you to hear an unusual clicking sound.

How is this symptom treated?

Typical forms of myoclonus don’t need care. For other types, the best approach can vary widely. Your provider will recommend treatment based on the underlying cause, your medical history and other factors. Because of this, a healthcare provider is the best person to tell you about your options and which ones they recommend.

Treatment may include:

• Medication(s) or changing your current prescription medications
• Botox® injections
• Deep brain stimulation (DBS)
• Transcranial magnetic stimulation (TMS)

Researchers are currently exploring precision medicine for certain causes of myoclonus. Ask your provider if a clinical trial is an option for you.

Can this symptom be prevented?

You can’t prevent the normal and essential forms of myoclonus.

But some of the secondary causes are preventable. You may also be able to reduce how often epileptic myoclonus happens or how severe it is. Some things you can do include:

• Avoid substance use: This means avoiding the use of nonprescription drugs and prescribed drugs in any way other than how your provider told you to take them.
• Protect your nervous system: Protective gear, like helmets and safety belts, can help prevent injuries to your brain and spinal cord.
• Manage chronic conditions: Managing conditions like epilepsy and thyroid disorders can help prevent muscle twitches or reduce how often they happen.