Chorea, The Dancing Illness

Chorea is a classical neurological illness, the name of which derives from both Latin and Greek referring to dance or choral dance. Chorea has been described since the Middle Ages and describes a syndrome of brief, rapid, abrupt, involuntary movements coming from random muscle contractions. The pattern of movement may at times give the impression that the patient is restless or fidgety. Chorea is an uncommon but nevertheless very interesting neurological condition. In the Middle Ages, the most common form of chorea was most likely Sydenham’s chorea, which is a postinfectious chorea related to side effects from rheumatic fever and antibodies in the bloodstream resulting from beta hemolytic group Streptococcus. The frequency of this disorder has declined continually over the years and it is very uncommon at this time.

Chorea can be caused by multiple conditions, the most important of which from a neurobiological perspective is Huntington disease or Huntington’s chorea. Huntington’s chorea is a slowly progressive, familial, neurogenetic disease that causes disorder of muscle control, emotional control, cognitive ability, and involuntary movements. Huntington disease was first well described by Dr. George Huntington when he concisely reported affected families in New York state in a paper "On Chorea and Choreiform Affectations" published in 1894. Chorea can also be caused by stroke, lupus erythematosus, or a variety of other less common genetic, infectious, and drug related causes.

Huntington disease is, arguably, one of the most important causes of chorea from neurobiological, social, and economic standpoints. Huntington disease is a genetic disorder of an autosomal dominant type which basically means that there is a 50% chance of inheriting the gene from an affected parent and, therefore, a 50% chance of inheriting the condition. These genes produce a protein called huntingtin which, with an abnormal huntingtin gene, is excessively produced and produces progressive neurodegeneration widely throughout the brain, but in particular in deep structures called the corpus striatum. Absence of the normal huntingtin gene causes embryonic death in mice and it seems that the normal huntingtin gene supports the normal health of nerve cells in the brain. It is felt that the excessive production of huntingtin gene produces its abnormal effects by a gain in function rather than a loss in function.

Prevalence of affected individuals in the United States is approximately 1 in 10,000 and with a resultant approximately 30,000 people affected. Since it is an autosomal dominant disorder, both sexes are equally predisposed to this disease and the disease is present worldwide. There is some prevalence correlated with European ancestry and Huntington disease is rare in Japan and China. There are no proven ways to prevent the onset or progression of Huntington disease. The diagnosis can be made on the basis of clinical presentation, adequate family history, physical findings, and genetic testing. Prognosis is, for a slowly progressive course, over 10 to 25 years. Emotional symptoms such as depression tend to occur in the early to middle stages of the disease with sleep disruption and motor decline in the middle to late stages of the illness.

Various medications are available to treat symptoms in chorea and a new medication has been approved by the FDA for treatment of the muscle movements themselves. Other treatment is available for psychiatric symptoms. Luckily, Huntington’s chorea is a very uncommon condition, but this condition is being actively pursued with scientific investigations using electronic and genetic testing.