clonus n : convulsion characterized by alternating contractions and relaxations

English

Etymology

Latin, from Greek κλονος ‘turmoil’.

Pronunciation

IPA: /'kləʊnəs/

Noun

clonus

1. a muscular spasm with regular contractions

Clonus (from the Greek for "violent, confused motion") is a series of involuntary muscular contractions due to sudden stretching of the muscle. Clonus is a sign of certain neurological conditions, and is particularly associated with upper motor neuron lesions such as amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis, spinal cord damage and hepatic encephalopathy. Magnesium Sulphate overdose is also know to cause clonus. Unlike the small, spontaneous twitching known as fasciculations (usually caused by lower motor neuron pathology), clonus causes large motions that are usually initiated by a reflex.

Clonus is most common in the ankles, where it is tested by rapidly flexing the foot upward (dorsiflexion). It can also be tested in the knees by rapidly pushing the patella towards the toes. Only sustained clonus (5 beats or more) is considered abnormal.

Clonus appearing after ingesting potent serotonergic drugs strongly predicts imminent serotonin toxicity.

See also

• Myoclonus
• Tonic-clonic seizure

External links

• Video demonstration of clonus at UCLA
• Dr. Gilman on Serotonin Toxicity