AskDefine | Define clonus

Dictionary Definition

clonus n : convulsion characterized by alternating contractions and relaxations

User Contributed Dictionary



Latin, from Greek κλονος ‘turmoil’.


IPA: /'kləʊnəs/


  1. a muscular spasm with regular contractions

Extensive Definition

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.
clonus in German: Klonus
clonus in Spanish: Clonus
clonus in French: Clonus
clonus in Lithuanian: Traukuliai
clonus in Japanese: クローヌス
clonus in Portuguese: Clônus
clonus in Chinese: 阵孪性状态
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