Clonus


Article Author:
Barret Zimmerman


Article Editor:
John Hubbard


Editors In Chief:
Kranthi Sitammagari
Mayank Singhal


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Abbey Smiley
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
7/28/2019 8:30:26 PM

Introduction

Clonus is a rhythmic, oscillating, stretch reflex, the cause of which is not totally known; however, it relates to lesions in upper motor neurons and therefore is generally accompanied by hyperreflexia.  Therefore, clonus is used as part of the neurological physical exam to evaluate the status of a patient’s nervous system.  It can be evaluated in many joints but is most commonly seen in the ankle joint by briskly dorsiflexing the foot.  An illustrative example of what clonus might look like is a clinician tapping the patellar tendon once lightly and a subsequent series of obvious repeated knee extensions and relaxations going on for a dozen beats. The test is free of cost, generally requires no equipment and can be performed rapidly and easily in a hospitalized patient.  Like other signs of upper motor neuron syndrome clonus indicates some insult to the central rather than peripheral nervous system; so part of its utility as a clinical examination skill is in differentiating the two.  It has other roles, for instance, it is prognostic of seizures in certain drug overdoses and therefore can be used to decide when to treat this condition prophylactically.  

Anatomy

The precise pathophysiology behind clonus is not known, but there are 2 leading theories.[1][2] In one, clonus is caused by a self-perpetuating reactivation of peripheral muscle stretch circuits, with each beat producing the next. In the other, there is an initial appropriate external stimulus that leads to activation of the stretch reflex circuit followed by a central signal which commands the muscles to continue to produce that motor response in the absence of an appropriate stimulation of the stretch reflex. A complete explanation may be a combination of the 2 theories.[2]

Hyperexcitability in muscle stretch circuits is produced when there is less tonic inhibition of motor neurons involved in the monosynaptic stretch reflex. This can occur when there is a lesion to descending motor nerves, predominantly the dorsal reticulospinal pathway, which can occur anywhere from the cortex to the spinal cord. The inhibitory dampening effect of these descending nerves on alpha and gamma motor neurons is removed, leading to a hyper excitatory state in the muscle stretch reflex circuit. Therefore, clonus is considered a manifestation of upper motor neuron pathology and this explains why other signs of hyperreflexia generally accompany it.

The rhythm of a given joint's clonus is defined by the nervous anatomy involved in that joint's stretch reflex. The longer the nerves involved, the longer it takes for a signal to be conducted to the spine and back out to the periphery, and therefore the longer the time between beats. For example, the wrist or fingers will oscillate at a higher frequency (shorter interval between beats) than the ankle which is significantly further from the spine.

The most common site to test for clonus is in the ankle/Achilles reflex (S1/S2 nerve routes). Some other commonly tested clonus reflexes include the[1]:

  • Jaw jerk/masseter: Trigeminal nerve, tested at the chin/mental protuberance
  • Patellar/quadriceps/knee: L2 to L4 (mostly L4), tested just inferior to the patella (or by pushing patella distally)
  • Biceps: C5 to C6, just anterior to elbow
  • Triceps: C7 to C8 (mostly C7), just posterior to the elbow

Equipment

One of the appealing aspects of clonus as a physical examination technique is that it can easily be performed without equipment. As it is most commonly tested at the ankle, with swift dorsiflexion of the entire foot, no equipment is required. Elsewhere, when testing other joints, for instance, the knee, the patellar tendon can be struck briskly with the fingers, or an improvised object like a stethoscope, or phone. However, as clonus is a mark of hyperreflexia, it is generally easy to elicit in a patient without much force, so the examiner’s fingers may even be preferred over other equipment.[3] If desired, a reflex hammer of any type would be adequate equipment to test this reflex.

Technique

Eliciting the clonus reaction can be done in the same manner as eliciting a muscle stretch reflex, which involves tapping the tendon of the joint when it is in a relaxed position often at ninety degrees of flexion (see MSR Statpearls article for a more detailed description of these techniques).[3] This article will focus on the clonus specific reflex maneuvers at the knee and ankle. In these cases, the examiner maintains sustained pressure on the joint which allows the clonus to be appreciated through tactile feedback and helps elicit this response.

For the ankle this involves allowing the patient to relax with a passively flexed ankle to about ninety degrees and a passively flexed knee if possible; this usually involves the examiner supporting the leg with the hand not performing clonus. Next, at the ankle, the examiner places their hand on the dorsum of the patient’s forefoot and briskly dorsiflexes it, after which the examiner continues to maintain dorsiflexion pressure. It is against this pressure that the clonus beats will be felt, and the rhythm and number of beats can be appreciated. Each beat will be felt as a plantarflexion followed by a relaxation. The initial beat is the longest, with decreasing duration of beats until the fourth beat, after which the beat frequency becomes equivalent from one to the next.[1] The initial brisk dorsiflexion and sustained pressure are sometimes done with slight eversion of the foot.

At the knee, the process is somewhat similar, but the positioning is different. The knee should be completely extended (passively) with the thigh and leg muscles completely relaxed. Then the patella is briskly moved distally using the examiner’s fingers, and light pressure is maintained in the distal direction. Each beat of clonus will be felt as a proximal movement of the patella followed by relaxation.

Clinical Significance

Clonus can be physiologic, for instance, term infants can be hyperreflexic, and a few beats of clonus can be a normal finding in this population; however, most infants will not exhibit this finding, and most infants who will go on to demonstrate cerebral palsy will not exhibit clonus.[4] In adults, it is generally pathological. If greater than 10 beats, it is considered "sustained clonus," which is sometimes denoted as a "5" when evaluating reflexes, or just documented in the text along with a rating of "4" which is otherwise the highest the reflex scale goes.

Clonus exists as a physical examination finding, but also as pathology in those with the condition. There is a range of impact on daily life among those with the condition, ranging from somewhat debilitating to a minor annoyance.[5] As a physical examination finding, clonus is a marker of hyperreflexia, which is part of an upper motor neuron syndrome. Therefore, it is generally accompanied by other upper motor neuron signs including positive signs like spasticity, and negative signs like weakness (which is also a lower motor neuron sign).[6] These signs, especially when taken together in in the right context, signal central nervous system insult, which can come in many varied forms, to only name a few: vascular (stroke), infectious (encephalopathy), congenital (cerebral palsy), autoimmune (multiple sclerosis), traumatic (spinal cord insult). Another significant category of pathology which can manifest as clonus would be iatrogenic or toxicological. Clonus is often evaluated in suspected serotonin syndrome, which can be brought on by many drugs including psychiatric (MAOI, SSRI, SNRI, TCA) or street drugs (cocaine, ecstasy, amphetamines) to name a few. Clonus has been identified as an effective way to predict seizures in patients who have overdosed on tramadol which is an SNRI.[7]

Enhancing Healthcare Team Outcomes

Part of what makes clonus a useful assessment is how quickly and easily it can be performed without specialized equipment or added cost. The test can be performed by nurses, medical students, the primary caregiver, or the specialist. It is commonly used to evaluate patients for which there is a concern for upper motor neuron syndrome, for instance, in patients at risk of stroke. Many types of clinicians are trained to perform clonus including nurses and physicians. The clearest way to document clonus findings is to explain what was found and how it was performed, but often, simply noting that reflexes are "4" or "5" is adequate.

If clonus is discovered on the physical exam, the nurse practitioner or primary care provider should refer the patient to a neurologist for further investigation. In addition, a pharmacist should be consulted to evaluate for drugs as an underlying cause. Once the etiology is determined, and a course of action undertaken, the interprofessional team will communicate to monitor for a successful outcome. [Level V]


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Clonus - Questions

Take a quiz of the questions on this article.

Take Quiz
Which of the following is an acceptable way to elicit clonus?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which is true if dorsiflexion of the foot produces sustained, rhythmic, alternating flexion and extension?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A young adult patient is dropped off outside the emergency department by her friends, and they drive off before any history can be obtained. The patient has altered mental status and shows signs of intoxication. Sudden dorsiflexion of her ankle produces a rhythmic reproduction of her ankle jerk reflex. Which of the following drugs did she most likely ingest?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 37-year-old soldier presents to the healthcare provider for follow up care after a blast injury that they received while serving overseas. As part of the neurologic examination, the provider tests for clonus. The patient has had bilateral amputations at the mid-shin. Which of the following is the best way to test for lower extremity clonus in this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A healthcare provider examines a 17-year-old male six weeks after the patient suffered a spinal cord injury. They have never met this patient, and while performing the neurological examination, they note the patient’s left knee oscillate while observing nearly ten contractions of the quadriceps group. What is the most specific physical examination findings in the left leg which the healthcare provider expects to find?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 65-year-old female with a history of osteoporosis is seen in the clinic for a fall. She had a cervical disc surgery 3 days ago. The provider elicits a rapidly alternating contraction and relaxation cycle in the lower extremity through a physical examination technique. Which of the following is the most appropriate way to specifically elicit this response?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 3-month-old male infant is being evaluated at a routine pediatric visit. Upon physical exam of the lower extremity and after swift dorsiflexion of the ankle, the clinician notices several rhythmic, oscillating extensions and relaxations of this joint. What is the most appropriate conclusion to be drawn from this result?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Clonus - References

References

Zimmerman B,Hubbard JB, Anatomy, Reflexes null. 2018 Jan     [PubMed]
Najari F,Alizadeh-Ghamsari A,Vahabzadeh M,Dadpour B,Reza Mousavi S,Baradaran Kayal I, A Study of the Importance of Clonus Symptoms in Patients with Tramadol Poisoning. Journal of toxicology. 2017     [PubMed]
Boyraz I,Uysal H,Koc B,Sarman H, Clonus: definition, mechanism, treatment. Medicinski glasnik : official publication of the Medical Association of Zenica-Doboj Canton, Bosnia and Herzegovina. 2015 Feb     [PubMed]
Ivanhoe CB,Reistetter TA, Spasticity: the misunderstood part of the upper motor neuron syndrome. American journal of physical medicine     [PubMed]
Beres-Jones JA,Johnson TD,Harkema SJ, Clonus after human spinal cord injury cannot be attributed solely to recurrent muscle-tendon stretch. Experimental brain research. 2003 Mar     [PubMed]
Mummidisetty CK,Bohórquez J,Thomas CK, Automatic analysis of EMG during clonus. Journal of neuroscience methods. 2012 Feb 15     [PubMed]
Hamer EG,La Bastide-Van Gemert S,Boxum AG,Dijkstra LJ,Hielkema T,Jeroen Vermeulen R,Hadders-Algra M, The tonic response to the infant knee jerk as an early sign of cerebral palsy. Early human development. 2018 Apr     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of PA-Hospital Medicine. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for PA-Hospital Medicine, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in PA-Hospital Medicine, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of PA-Hospital Medicine. When it is time for the PA-Hospital Medicine board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study PA-Hospital Medicine.