Hemichorea as a presentation of acute rheumatic fever.

There has been a decline in the incidence of acute rheumatic fever in recent decades in developed countries and in Taiwan. Sydenham's chorea, a major manifestation of rheumatic fever, was the most common cause of chorea in children in the past. But the incidence of Sydenham's chorea has declined in recent years in concert with the decline in rheumatic fever. Sydenham's chorea is usually bilateral and female predominant. Hemichorea is rare. We report on a 10-year-old boy who presented with progressive right side involuntary movements, an apical systolic murmur, prolonged PR interval, and elevated antistreptolysin O titer, who was diagnosed with acute rheumatic fever.