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Clonus
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<embedvideo service="youtube" alignment="right">https://www.youtube.com/watch?v=Ji_cidY70zc</embedvideo>The video demonstrates sustained ankle clonus in a patient with a spastic hemiparesis after a stroke. Clonus is a series of rhythmic involuntary muscular contractions induced by the sudden passive stretching of a muscle or tendon. It often accompanies the spasticity and hyperactive DTRs seen in corticospinal tract disease. Clonus occurs most frequently at the ankle, knee, elbow and wrist, occasionally elsewhere. The response is a series of alternating contractions of the agonist and antagonist. Ankle clonus consists of a series of rhythmic alternating flexions and extensions of the ankle. Unsustained clonus fades away after a few beats, sustained clonus may persist as long as the examiner continues to hold slight pressure against the sold of the foot. Unsustained (transient, exhaustible), symmetric ankle clonus may occur in normal individuals with physiologically fast DTRs. Sustained clonus is never normal.
==References==
Campbell WW. DeJong's the neurologic examination, 7th ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2013.
[http://www.nejm.org/doi/full/10.1056/NEJMicm1512677#t=article do Rosário MS. Clonus Associated with Tropical Spastic Paraparesis. N Engl J Med. 2016;375:e34 ]
Fareedy SB, Pathak R. Ankle clonus. Clin Case Rep. 2015;3:520.