Clonus
Pronunciation: KLOH-nus
A series of rhythmic, involuntary muscular contractions and relaxations elicited by a sustained stretch reflex, typically indicating an upper motor neuron lesion.
Full Definition
Clonus is a neurological finding documented in PM&R evaluations as a marker of upper motor neuron (UMN) pathology, such as occurs in spinal cord injury, stroke, cerebral palsy, or multiple sclerosis. It is most commonly elicited at the ankle (ankle clonus) by rapid dorsiflexion, though it can occur at the knee or wrist. In clinical documentation, clonus is graded by number of beats (e.g., 'three-beat ankle clonus') or described as sustained vs. unsustained. Editors should note that clonus is a specific subset of hyperreflexia and is not synonymous with spasm or myoclonus. The term is always written in lowercase and should not be hyphenated.
Usage
Usage note: Clonus is distinct from myoclonus (brief shock-like jerks) and tremor (oscillatory). Specify the joint and number of beats in clinical documentation.
In Context
- "Neurological examination revealed sustained ankle clonus bilaterally, consistent with cervical myelopathy." — Inpatient physiatric consultation note
- "The editor queried whether 'clonus' had been confused with 'myoclonus' in the neurology section of the report." — Medical records review