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 in stroke, multiple sclerosis, spinal cord damage and hepatic encephalopathy. 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 (serotonin syndrome).
http://en.wikipedia.org/wiki/Clonus

info DE
http://books.google.de/books?id=iudj5uu21Z0C&pg=PA627&lpg=PA...




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Note added at 16 mins (2009-10-23 16:41:28 GMT)
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clonus (sg), cloni (pl)

By the way - it would be nice you could close previous questions of your´s (e.g. http://www.proz.com/kudoz/german_to_english/medical_general/... either just-close or award the points - otherwise one might get the feeling that you do not care for the answers and discussions - which hopefully is not the case;)
Best wishes