Clonus
Pronunciation: KLOH-nus
Rhythmic, involuntary muscle contractions triggered by sudden stretching, indicating upper motor neuron dysfunction and hyperreflexia.
Full Definition
Clonus is a neurological sign characterized by repetitive, rhythmic muscle contractions and relaxations that occur when a muscle is suddenly stretched and maintained in that stretched position. This phenomenon indicates hyperexcitability of stretch reflexes due to upper motor neuron lesions, commonly seen in spinal cord injuries, stroke, or multiple sclerosis. Clonus most frequently occurs in the ankle (ankle clonus) when the foot is suddenly dorsiflexed, but can also be elicited at the knee (patellar clonus) and wrist. In rehabilitation, sustained clonus may interfere with functional activities and requires management through positioning, stretching, and sometimes antispasmodic medications.
Usage
Usage note: Describe the duration (beats) and sustainability when documenting clonus findings.
In Context
- "Sustained ankle clonus lasting more than 10 beats indicates significant upper motor neuron involvement." — neurological examination
- "Clonus at the ankle interferes with standing balance and requires antispasticity intervention." — rehabilitation assessment