What does clonus mean?
Clonus is a medical term describing a series of involuntary, rhythmic contractions and relaxations of a muscle, most commonly observed at the ankle or knee. It occurs when the nerve pathways that normally dampen reflex activity — the upper motor neurons — are damaged or diseased, as in stroke, multiple sclerosis, spinal cord injury, or cerebral palsy. Physicians elicit it by briskly dorsiflexing the foot: a few beats of clonus can be unremarkable, but sustained, repeated beating is considered an abnormal sign warranting further investigation. The word derives from the Greek 'klonos', meaning tumult or violent motion, and entered English through nineteenth-century neurology. Because it is almost exclusively found in clinical settings — case reports, examination notes, and textbooks — clonus remains unfamiliar to most lay readers, yet it serves as one of neurology's classic physical signs of corticospinal tract dysfunction.
nounA series of involuntary, rhythmic muscular contractions and relaxations, typically occurring in medical contexts as a sign of neurological injury or disease.
- Involuntary, rhythmic alternation of muscle contraction and relaxation, most often observed at the ankle or knee, indicating upper motor neuron dysfunction.
"The neurologist noted sustained ankle clonus in the patient's right leg during the examination."
"Sustained clonus at the ankle prompted the physician to order an MRI of the brain and spinal cord."
"In severe cases, clonus can be triggered simply by stretching the affected muscle."
The plural is rare in practice, since clonus is usually discussed as a single clinical finding per patient or limb; when pluralized, 'clonuses' is standard.
"Bilateral ankle clonuses were recorded during the neurological assessment."
Doctors test for clonus by flicking your foot upward — a few beats can be normal, but sustained clonus signals the spinal cord or brain may be in trouble.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of clonus
Clonus comes from the ancient Greek noun 'klonos', meaning tumult, confusion, or violent motion. The term was adopted into English medical vocabulary in the nineteenth century as neurologists formalized the clinical examination of reflexes. It shares its Greek origin with the related adjective 'clonic' and with terms such as 'myoclonus', all describing forms of involuntary muscular movement.
Related word forms
How clonus is actually used
Strictly a clinical term used by neurologists and other physicians; it rarely appears outside medical writing. It carries no emotional connotation but signals a potentially serious neurological finding when documented in an examination.
Easily confused with clonus
A clone is an identical genetic or digital copy of an organism or object, whereas clonus is a rhythmic muscular spasm of neurological origin.
Clonic is an adjective describing the phase of a seizure marked by rhythmic jerking, while clonus is the noun naming the rhythmic contractions themselves.