Huntington’s disease (HD), also known as Huntington’s chorea, is one of the most common causes of chorea. In fact, nine out of 10 people with HD will develop chorea at some point during the course of their illness.
Chorea refers to a range of involuntary movements. It’s a disorder of the nervous system, and one of a group of disorders called hyperkinetic disorders. This term draws attention to the fact that, in chorea, there’s excessive movement, called choreic movements.
Choreic movements result from muscle contractions – mainly in the hands, forearms, lower legs, face and sometimes the chest. These uncontrollable movements are rapid and jerky, occurring with irregular and unpredictable timing. They often differ from those found in the normal repertoire of movements and so, apart from being abrupt and purposeless, they may also have an abnormal appearance.
Choreic movements tend to flow from one part of the body to adjacent parts, giving the impression of dancing. In fact, the term “chorea” is derived from the Greek word meaning “to dance”.
Chorea usually affects both sides of the body, but in some instances only one side of the body is involved. This is referred to as “hemichorea”.
Choreic movements in the face include frowning, raising the eyebrows, pursing the lips and smiling. Grimacing, which usually takes the form of caricatures of normal facial expressions, also occurs. The muscles of the jaw and tongue may be involved, and involuntary movements of these can impair chewing and swallowing.
Sometimes muscles in the chest and diaphragm are affected, which can cause jerky and irregular breathing. This may be accompanied by abnormal respiratory sounds such as grunts and gasps. Speech may also be impaired, becoming slurred, erratic or explosive, due to the effects on the muscles used in breathing as well as from involuntary tongue movements.
Choreic movements disrupt voluntary movement, so people with chorea may appear clumsy and sometimes walk with a wide, swaying or lurching gait.
Chorea often occurs together with athetosis, a condition characterised by slow, writhing movements of the limbs. When this occurs, the combined set of movements is referred to as choreoathetosis.
In severe cases of chorea, movements sometimes occur as a violent flinging of the limbs, which results in severe, uncontrollable flailing. These are called ballistic movements, and this condition is known as ballism or choreoballism. Ballistic movements can be severely debilitating and even lead to injury.
Choreic movements disappear during sleep, but tend to get worse when a person is anxious, stressed or distracted.
Causes of chorea
A set of structures in the brain, called the basal ganglia, form an integral part of a larger system that controls the muscles responsible for bodily movements. Dopamine, a neurotransmitter, plays an important role in the functioning of the basal ganglia. (Neurotransmitters are chemicals that control transmission of nerve impulses between nerve cells.)
HD is one of the disorders that cause dopamine to become overactive in nerve pathways within the basal ganglia. This, in turn, causes choreic movements.
Drugs are available to treat the symptoms of chorea. Most of these work by suppressing the activity of dopamine.
Unfortunately, these drugs often have severe side effects, such as sedation and muscular rigidity. For this reason, drugs are seldom used in mild cases of chorea that don’t cause significant embarrassment or disability.
Treatment with drugs is usually successful in cases where unpleasant side-effects don’t occur. In many instances, however, the side effects of the drugs prove to be debilitating or intolerable. In these cases, low drug dosages have to be used, achieving only partial suppression of symptoms.
With HD, onset of symptoms is usually gradual, but the disease progresses relentlessly and eventually causes full-blown chorea and profound dementia. HD is therefore severely disabling and ultimately fatal. The duration of the illness ranges from 10 to 25 years.