Clonus

What is clonus?

Clonus is an abnormal reflex response that involves involuntary and rhythmic muscle contractions. It happens in response to a brisk muscle stretch.

A reflex is an involuntary (automatic) action your body does in response to stimulation. Reflexes normally protect your body from things that can harm it.

Healthcare providers test for clonus as part of a neurological exam. They do this by testing your muscle stretch reflexes at various joints. These tests show how well the nerves between your spinal cord and body communicate.

Providers most commonly see clonus in your ankle joint when they briskly flex your foot up toward your shin. If you have clonus, your foot will then involuntarily bounce up and down. This bouncing may stop spontaneously or it may continue for as long as the provider applies pressure to the bottom of your foot. In severe cases, simply walking can trigger clonus at your ankles. These extra bounces interfere with your gait pattern.

Clonus can also exist in your:

• Knees.
• Wrists.
• Fingers.
• Jaw.

Clonus is a manifestation of hyperreflexia, which is when your muscles have an overactive reflex response. For example, providers often test your muscle reflexes by tapping your knee with a rubber hammer. If you have hyperreflexia, your leg will kick out farther and more quickly than normal.

Clonus can indicate an underlying problem with your nervous system. Depending on how severe it is, the underlying issue could be affecting:

• How you walk (gait).
• Your posture.
• How well you perform daily tasks.

What does it mean if you have clonus?

If you have clonus, it usually means that you have damage somewhere in your central nervous system (brain or spinal cord). This damage could be:

• Temporary (such as from an infection).
• An acute change (such as from a spinal cord injury).
• Due to a chronic condition.

If your provider observes that you have clonus during a neurological exam, they’ll order tests to determine the underlying cause. These tests may include:

• Certain blood tests.
• MRI scan of your brain and/or spinal cord
• Nerve conduction studies and electromyogram.
• Spinal tap (lumber puncture).

What’s the difference between clonus and myoclonus?

Myoclonus is a brief, involuntary, irregular twitching of a muscle or a group of muscles. Clonus is an abnormal reflex response to a muscle stretch that involves rhythmic movement.

There are several forms of myoclonus. Some are normal or harmless (such as hiccups) while others happen as part of an underlying condition, such as epilepsy or multiple sclerosis.

Certain central nervous system conditions can cause both clonus and myoclonus.

What causes clonus?

Clonus typically happens as a result of an upper motor neuron lesion.

An upper motor neuron lesion means there’s been damage to certain nerve cells in your brain and spinal cord that help you move. Upper motor neuron lesions interfere with the normal signals that travel from your brain to your spinal cord and, ultimately, to your muscles.

Clonus usually occurs along with spasticity and muscle weakness as part of upper motor neuron syndrome.

Together, these signs point to an issue with your central nervous system (your brain and/or spinal cord). Several central nervous system conditions that involve an upper motor neuron lesion can cause clonus, including:

• Stroke.
• Brain tumor.
• Traumatic brain injury.
• Brain infections, such as meningitis or encephalitis.
• Spinal cord injury.
• Cerebral palsy.
• Multiple sclerosis.
• Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease.

Serotonin syndrome can also cause clonus. Serotonin syndrome is a potentially life-threatening drug reaction that results from having too much serotonin in your body.

How is clonus treated?

Treatment for clonus depends on the underlying cause and how mild or severe the clonus is. Healthcare providers make every effort to treat the underlying cause if possible. Providers can also use treatments to reduce the severity of clonus.

General treatments for clonus include:

• Applying a cold compress: Several studies have revealed that applying a cold compress, such as a bag of ice wrapped in a towel, can inhibit clonus. One study showed that the longer the period of cold application, the longer it took for clonus to recur (come back). Talk to your healthcare provider about how and when you should use cold compresses for clonus.
• Medications: Muscle relaxants, such as baclofen and tizanidine, can help treat clonus in addition to spasticity, which often occur together.
• Botulinum toxin (Botox®) or phenol injections: Providers inject botulinum toxin into the affected muscle to weaken or temporarily paralyze it so it can’t involuntarily contract. These injections usually last up to three months. Providers inject phenol close to the affected nerve root. These injections immediately block nerve conduction, causing the affected muscle to relax.

Can clonus be prevented?

As clonus results from an underlying neurological condition, to prevent it you would have to prevent getting the underlying condition. Once the underlying condition is present, there’s nothing you can do to prevent the clonus from developing.

When should clonus be treated by a healthcare provider?

You may not be able to tell if you have clonus without a neurological exam.

However, clonus often occurs alongside other symptoms, including spasticity (when certain muscles contract all at once), muscle weakness and fatigue. If you notice a change in how your muscles are working, it’s important to see a healthcare provider. It may be a sign of an underlying neurological condition.

A note from Cleveland Clinic

Clonus is an abnormal reflex response that involves involuntary and rhythmic muscle contractions. It can be a sign of an underlying medical condition, such as a brain injury or cerebral palsy. But you may not know you have clonus until a healthcare provider checks your reflexes. If you notice an unexplainable decline in your muscle strength and/or have other symptoms, it’s important to see a provider.