Chorea and athetosis aren't diseases; rather they are symptoms that can result
from several very different diseases. People with chorea and athetosis have abnormalities in the basal ganglia of the brain.
(see page 279 in Chapter 59, Biology of the Nervous System)
The basal ganglia's job is to smooth out the coarse movements that are initiated
by commands from the brain. In most forms of chorea, an excess of the neurotransmitter dopamine in the basal ganglia disrupts
its fine-tuning function.
Drugs and illnesses that alter dopamine levels or the brain's ability to recognize
dopamine can make chorea worse.
The disease that most often produces chorea and athetosis is Huntington's
disease, but it is fairly rare, affecting fewer than 1 in 10,000 people.
Sydenham's disease (also called St. Vitus' dance or Sydenham's
chorea) is a complication of a childhood infection caused by certain streptococci; it can last for several months.
Chorea sometimes develops in the elderly for no apparent reason and affects particularly the muscles in and around the
mouth. It also can affect women in the first 3 months of pregnancy, but it disappears without treatment shortly after they
Chorea that develops as a drug's side effect may improve if the drug is stopped,
but the chorea doesn't always disappear. Drugs that block dopamine's action, such as antipsychotic drugs, may help control
the abnormal movements.