clonus
Pronunciation: KLOH-nus
A series of involuntary, rhythmic muscle contractions and relaxations triggered by a sudden stretch reflex, commonly assessed in rehabilitation to evaluate upper motor neuron dysfunction.
Full Definition
Clonus is a sign of hyperreflexia caused by damage to descending motor pathways, and it is frequently documented in patients with spinal cord injury, stroke, or multiple sclerosis. It is elicited clinically by a rapid, sustained stretch of a muscle group—most often at the ankle—and is graded by the number of beats or classified as sustained versus unsustained. Editors must not confuse clonus with fasciculation (which involves lower motor neuron pathology) or with tremor (which is rhythmic but not stretch-induced). In documentation, clonus findings are often paired with reports of spasticity, though the two terms refer to distinct phenomena.
Usage
Usage note: Always lower-case. Do not use interchangeably with 'spasticity'; clonus is a distinct clinical sign, though both reflect upper motor neuron lesions.
In Context
- "Ankle clonus of five beats was recorded bilaterally, consistent with incomplete cervical spinal cord injury." — Spinal cord injury neurological assessment
- "The physiotherapist noted sustained clonus at the right ankle, which had not been present at the previous session." — Inpatient rehabilitation progress note