What is St Vitus’s dance?

St Vitus’s Dance is a name given to the disease chorea. It is a convulsive disease of the nerves usually associated with rheumatic fever. When someone gets chorea, the muscles - particularly of their hands, feet and face - move irregularly and involuntarily.
The name St. Vitus’s Dance dates from the late Middle Ages, when hysterical dancing (similar to the dancing of dervishes and voodoo cultists) was very popular. People in the grip of this hysteria often went to the chapels of St Vitus, who was believed to have great healing powers.
Chorea is chiefly a disease of childhood, occurring most often between the ages of five and 15. It is more common in girls than in boys. Sometimes the disease is mild. Sometimes it completely incapacitates the sufferer. It is quite usual for someone with the disease to be unable to hold objects or to write properly, and to have difficulty in walking. Recovery is hastened by rest in bed in a sympathetic environment.
Facial grimaces and tics are frequently confused with chorea, but these repetitive movements are quite different from the uncoordinated, purposeless movements of the disease.