Understanding Clonus for Student Nurses
Learn what clonus is, how it may appear during neurological assessment and why it should be interpreted alongside tone, reflexes, strength and the wider neurological picture.
What is clonus?
Clonus is a rhythmic, repetitive muscular response that may be observed during neurological examination. It is commonly discussed alongside muscle tone and deep tendon reflexes.
The patient is not producing it deliberately
The movement occurs automatically following the appropriate neurological stimulus.
The movement repeats
Clonus has a repetitive pattern rather than appearing as one isolated movement.
It needs clinical context
Its significance depends on the wider neurological examination and the patient's clinical presentation.
Where might clonus be assessed?
Clonus may be assessed as part of a more detailed neurological examination. The ankle is a commonly assessed site, although other joints can also demonstrate clonus.
A commonly assessed site
A trained clinician may assess for repetitive ankle movement during neurological examination.
Other joints can be involved
Clonus may also be assessed elsewhere when clinically appropriate.
Understand before performing
Observe and understand the significance of the assessment, and perform it only when appropriately trained and supervised.
What does clonus look like?
More than a single response
The joint may move repeatedly in a rhythmic pattern following the stimulus.
Comparison can matter
A difference between corresponding limbs may contribute useful information to the neurological assessment.
Look beyond clonus
Tone, reflexes, strength and functional movement should also be considered.
Clonus fits into a wider neurological pattern
Is muscle tone altered?
Increased tone and clonus may be considered together during neurological assessment.
Are reflex responses different?
Reflex findings provide additional information about neurological pathways.
Is there weakness?
Compare limb strength and look for new unilateral changes.
Has feeling changed?
New numbness or altered sensation may form part of the wider neurological presentation.
Is movement controlled?
Assess whether there is associated loss of coordination or a new functional change.
Has mobility changed?
New difficulty walking, transferring or using a limb may be more immediately apparent than the examination finding itself.
Clonus becomes clinically meaningful when interpreted alongside tone, reflexes, strength, sensation, coordination and the patient's baseline.
Clonus is not the same as tremor
Both can involve repetitive movement, but they are different clinical phenomena and should not be used interchangeably.
Triggered rhythmic response
Clonus is elicited by an appropriate stretch during neurological examination.
Rhythmic involuntary movement
Tremor may be visible during rest, posture or movement depending on its characteristics.
Describe what you observe
Avoid applying a neurological label when you are uncertain about the nature of an abnormal movement.
When neurological findings require escalation
- New unilateral limb weakness or loss of normal movement.
- Rapidly worsening weakness or neurological function.
- New abnormal neurological findings with facial weakness.
- New neurological changes with dysarthria or aphasia.
- Neurological abnormalities associated with sensory loss.
- New abnormalities following significant head or spinal injury.
- New neurological signs associated with seizure activity.
- Neurological deterioration associated with reduced consciousness.
Start with the patient, not the specialist test
Recognise change
Identify new weakness, altered movement, abnormal posture or deterioration from baseline.
Assess systematically
Use ABCDE when the patient is acutely unwell and assess neurological function appropriately.
Connect the signs
Consider consciousness, pupils, speech, facial movement, strength, sensation and coordination.
Escalate concerns
Communicate significant new abnormalities promptly rather than waiting for a definitive diagnosis.
Keep neurological assessment within ABCDE
Airway
Confirm airway patency and respond immediately to compromise.
Breathing
Assess respiratory rate, oxygen saturation, pattern and work of breathing.
Circulation
Assess pulse, blood pressure and perfusion within the wider clinical picture.
Disability
Assess consciousness, pupils, speech, strength, sensation, coordination and other neurological findings according to local practice.
Exposure
Look for injury, illness and other relevant findings while maintaining patient dignity.
Escalate
Report significant deterioration promptly using the appropriate local clinical pathway.
Connecting clonus with the wider assessment
Example
A patient is reviewed because their walking has become significantly more difficult.
During neurological examination by an appropriately trained clinician, increased tone and an abnormal repetitive ankle response are identified in one leg.
You have also observed weakness and a clear change from the patient's normal mobility.
The important pattern is: functional deterioration + weakness + abnormal tone + abnormal neurological response.
These findings are communicated and assessed within the wider neurological and clinical picture.
Describe the whole pattern
Example escalation
“Mr Taylor's mobility has deteriorated significantly compared with this morning. His left leg is weaker and during neurological review increased tone and a repetitive ankle response were identified on that side.”
This communicates the change from baseline, functional deterioration, side affected and associated neurological findings.
Clonus assessment errors to avoid
- Using clonus as a diagnosis rather than a neurological sign.
- Confusing clonus with tremor or other involuntary movement.
- Trying to perform specialist testing without appropriate training.
- Interpreting the finding without considering tone and reflexes.
- Ignoring side-to-side differences and previous baseline.
- Focusing on the examination instead of functional deterioration.
- Using specialist terminology when simply describing the observation would be clearer.
- Delaying escalation while attempting to complete a detailed neurological examination.
Recognise → connect → communicate → escalate
Notice neurological change
Start with weakness, altered movement, mobility and other changes from the patient's baseline.
Build the neurological picture
Connect clonus with tone, reflexes, strength, sensation, coordination and function.
Act on significant change
Clearly describe what has changed and escalate significant neurological deterioration promptly.
Connect neurological signs rather than memorising them in isolation
Clonus is most useful when understood alongside tone, reflexes, strength, sensation, coordination, function and the patient's normal neurological baseline.
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