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Irregular, alternating muscular contractions and relaxations.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



rhythmic contractions, in rapid succession, of single muscles or muscle groups. Clonus may be either spontaneous or provoked by external stimulation.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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(1) Lack of ankle clonus in patients with acute tramadol poisoning
Ankle clonus was defined as the plantar reflection of rhythmic movements in response to a sudden stretch held in muscles and sustained clonus was defined as the presence of five or more beat means of ankle clonus [9].
Clinicians that only use Babinski sign and ankle clonus in the lower extremities to evaluate for the possibility of upper motor neuron disease should consider expanding the scope of their neurologic evaluation.
Possibly affected' members are asymptomatic at- risk subjects who have a normal gait but who show possible corticospinal tract deficits on examination (mild hyper-reflexia a few beats of unsustained ankle clonus but with flexor plantar responses).
On neurological examination, Glasgow coma scale was 6/15, pupils were equally reactive, deep tendon reflexes were brisk, plantar responses were extensor and bilateral ankle clonus was noted.
Abnormal deep tendon reflexes, crossed adductors, and ankle clonus are other signs of upper motor neuron lesions.
Reflexes were brisk with bilateral spontaneous ankle clonus of both ankles.
Ankle clonus of one to three beats is normal in an infant during the first few months of life, but sustained clonus is not.