What Is Clonus?

Table of Contents
View All
Table of Contents

Clonus is a reflex which refers to involuntary, repetitive, and rhythmic muscle contractions. This abnormal reflex is due to a lesions in descending motor neurons, which are those responsible for motor function, muscle tone, reflex strength, and more. Clonus can be observed throughout the body, but is most commonly seen in the biceps, triceps, patella, and ankle regions.

This article reviews the causes, diagnosis, and treatment of clonus.

Reflexes being checked for clonus

kali9 / Getty Images

Causes of Clonus

Clonus is a type of stretch reflex, meaning that when a muscle group is stretched or stimulated, neurons perceive that stretch and cause contraction of the same muscle group. This type of reflex is meant to protect against strains and muscle tears. With clonus, however, the normal contraction occurs not once but several times before subsiding.

While the exact cause of clonus remains unclear, clonus can be seen in a number of different diseases affecting the nervous system.

Common Causes of Clonus

Clonic movements can also be observed in the context of seizures, side effects of certain medications, and chemical imbalances.

Clonus and MS

Multiple sclerosis (MS) is a chronic autoimmune inflammatory disease in which the immune system destroys the protective sheath covering nerve cells, known as myelin. This damage leads to miscommunications between the brain and other areas of the body, as well as a lower trigger threshold for stretch reflexes.

Given the nature of the disease, people with MS often experience clonus, as well as other symptoms like involuntary muscle spasms, tremors, muscle weakness, and spasticity. Other symptoms include sensory loss, coordination issues, and cognitive impairment.

Clonus and Spasticity

Spasticity is often seen in people with neurological diseases. It refers to abnormal muscle tightness or contraction.

In addition to painful muscle spasms, spasticity can also lead to clonus, pain, permanent muscle contractures, joint deformities, and even decreased ability to perform activities of daily living.

How Clonus Is Diagnosed

Clonus can be observed during the physical examination portion of a medical appointment. Depending on the area affected, a healthcare provider can apply stress or "stretch" a muscle or tendon and observe the subsequent response or reflex. With clonus, the healthcare provider can then measure or count the number of involuntary contractions which occur.

Once clonus is observed, it becomes incredibly important to try and determine the cause of the neurologic issue. To get to the root cause of clonus, a healthcare provider may order:

  • Specific blood tests
  • MRI scan of the brain and/or spinal cord
  • Nerve conduction studies
  • Lumbar puncture (spinal tap)

Treatment for Clonus

When it comes to managing clonus, there are several oral medications and alternative therapies that can be beneficial.

While there is no "one-size-fits-all" therapy, a tailored treatment regimen managing both the symptoms and the underlying disease can increase a person's quality of life.

The treatment of clonus due to chemical imbalances, seizure, or medication side effects is to correct these acute medical problems.

Medications

The goal of oral medications used to manage clonus due to spasticity is to relax the affected muscles and decrease rigidity. Some of these medications include:

  • Muscle relaxants, such as baclofen and tizanidine
  • Benzodiazepines, such as diazepam and clonazepam

These medications should be used with caution, as they come with side effects. These include, but are not limited to, drowsiness, dizziness, and fatigue.

Other Therapies

Targeted injections of either botulinum toxin A/B or phenol may provide relief for clonus.

Botulinum toxin is typically injected within the affected muscle, weakening or temporarily paralyzing specific muscles so they can not involuntarily contract. It can take up to 10 days before results are noticeable and increased range of motion and function may be observed. If successful, these injections could provide relief for several months.

Unlike botulinum toxin injections, phenol injections are administered close to the affected nerve roots and immediately block nerve conduction, causing the muscle to relax. If effective, phenol injections may also provide several months worth of relief.

Physical Therapy for Clonus

Physical therapy is a conservative but potentially transformative option for clonus management. A licensed physical therapist can help stretch and strengthen affected muscles, leading to increased mobility and functionality. They can also recommend if and when splints or braces may be viable options to give additional support, especially when clonus affects the lower extremities and can impeded proper mobility.

Surgery

If all other treatment options fail, a healthcare provider may recommend surgery to alleviate clonus. Surgery can either be done to release a tendon which has become inflamed and caused a contracture of the underlying muscle, or it can be done to sever the affected neuron-muscle pathway.

While these surgeries may relieve clonus, they can also lead to permanent and disabling limited mobility and muscle functionality.

Home Remedies for Clonus

In conjunction with other modes of treatment, the application of cold packs to affected areas and vigilant performance of at-home stretching exercises can also help reduce the severity of clonus.

Outlook

While there are several treatment options to help alleviate clonus, the severity and prognosis really depends on the underlying cause. Clonus can range from a mild annoyance to a disabling reflex.

Adequate management of the underlying disease or cause, if possible, can result in minimization of clonus.

Summary

Clonus can refer to the involuntary and repetitive muscle contractions that occur after stimulating a muscle. Common causes of clonus include multiple sclerosis, cerebral palsy, spinal cord or traumatic brain injuries, and more. It is also seen in the context of certain seizures, medication side effects, or chemical imbalances.

Through a thorough history and physical examination, a healthcare provider will be able to diagnose clonus and offer treatment options such as physical therapy, medications, targeted injections, and surgery. The prognosis for clonus depends on the underlying cause and how effectively it can be managed.

A Word From Verywell

Clonus can range from inconvenient to disabling. If you are suffering from clonus, it's important to speak with your healthcare provider about your symptoms. Management of clonus requires multi-disciplinary collaboration between neurologists, orthopedists, physical therapists, and others. Thankfully, there are several treatment options available which can help manage clonus.

Frequently Asked Questions

  • What is clonus reflex?

    Clonus refers to involuntary and repetitive muscle contractions that occur in response to stimulation. Clonus is typically due to lesions in descending motor neurons. They can be observed throughout the body, but are most commonly seen in the jaw, biceps, triceps, patella, and ankle regions.

  • What is a positive clonus test?

    A clonus test is performed when a healthcare provider applies a force or stretch to an area—the ankle, for example—and upon release of the stretch, the ankle begins involuntarily and rhythmically bobbing up and down. This is considered a positive clonus test. Resulting movements will vary based on the area being tested, but this type of movement is indicative of clonus.

  • What triggers clonus?

    Clonus is a type of stretch reflex. When a muscle is being stimulated or stretched, nerve impulses from the muscle get sent to the brain, which in turn sends a message to the muscle to contract in defense. Over-stretching, an injury, or certain neurological deficits can all trigger a clonus reflex.

  • What is the difference between clonus and myoclonus?

    Whereas clonus is the rhythmic, involuntary contraction of muscles, myoclonus refers to brief and sudden involuntary muscle twitches.

Was this page helpful?
5 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. Boyraz I, Uysal H, Koc B, Sarman H. Clonus: definition, mechanism, treatment. Medicinski Glasnik. 2015;12(1):19-26.

  2. Bhattacharyya K. The stretch reflex and the contributions of C David Marsden. Ann Indian Acad Neurol. 2017;20(1):1. doi:10.4103/0972-2327.199906

  3. Epilepsy Foundation. Clonic seizures.

  4. Manca M, Merlo A, Ferraresi G, Cavazza S, Marchi P. Botulinum toxin type A versus phenol. A clinical and neurophysiological study in the treatment of ankle clonus. Eur J Phys Rehabil Med. 2010;46(1):11-18.

  5. National Institute of Neurological Disorders and Stroke. Spasticity information page.