What is the cause of this child's bizarre movements?

9 y/o male with no previous medical history presents with gradual onset of bizarre movements over the past 3 days. He had a sore throat about two months ago which resolved without antibiotic treatment. ROS otherwise negative. Vitals stable. Exam notable for bizarre movements (see video below). What is your diagnosis?

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Sydenham chorea, one of he major clinical manifestations of acute rheumatic fever.   Occurs 1 to 8 months after inciting group A strep infection.  Some patients may have associated arthritis, carditis and/or psychiatric symptoms.  Diagnosis is clinical but may be supported by positive ASO titer.  Other causes of chorea which should be excluded include encephalitis, thyrotoxicosis, lupus, Wilson's disease and Huntington disease.  Treat with corticosteroids and antibiotics. 

Source 

Cruse, R. "Sydenham chorea"  Up to Date. Sept 2007.

Image source: http://www.youtube.com/watch?v=RsIQFeYOkAg