Chorea is a hyperkinetic movement disorder characterized by an excess of involuntary motion. The term is derived from the ancient Greek word choreia, meaning “dance.” This reflects the condition’s most noticeable characteristic: movements that appear unpredictable, flowing, and seemingly dance-like. These movements can significantly interfere with normal daily activities.
Characteristics of Chorea Movement
Chorea is defined by involuntary, abrupt, brief, and irregular movements that are non-stereotyped, meaning they do not follow a predictable pattern or rhythm. These movements often appear to “flit” randomly from one muscle group to another, giving the impression of continuous restlessness or fidgeting. The motion can involve the face, trunk, and extremities, often leading to an unstable, dance-like gait.
Movements in the hands and fingers can manifest as “milkmaid’s grip,” where the patient cannot maintain a steady grip when asked to squeeze the examiner’s fingers. When trying to stick out the tongue, it may dart in and out uncontrollably, sometimes called “harlequin tongue.” People affected frequently attempt to mask these involuntary jerks by incorporating them into seemingly intentional actions, such as shifting position or adjusting clothing.
The severity of chorea exists on a spectrum. In its mildest form, it may present as simple fidgeting or slight exaggerations of normal gestures. The most violent, large-amplitude form is called ballism, which typically involves flinging movements of the limbs, often affecting only one side of the body (hemiballism). These movements tend to worsen with anxiety or stress and disappear entirely during sleep.
The Neurological Mechanism Behind Chorea
The involuntary movements of chorea originate from dysfunction within the brain’s basal ganglia, a group of deep gray matter structures responsible for initiating and regulating voluntary movement. These structures, particularly the striatum, act as a control center, balancing signals to ensure smooth and coordinated motion. The basal ganglia utilize two main pathways—direct and indirect—to modulate movement, with the indirect pathway normally inhibiting unwanted motion.
In chorea, the primary issue is an imbalance that leads to reduced inhibitory signaling from the basal ganglia to the motor cortex. This loss of inhibition results in an over-excitation of the motor thalamus and the cerebral cortex, generating the excessive and uncontrolled movements. This functional disruption is often linked to an overactivity of the neurotransmitter dopamine in the striatum. Medications that block dopamine receptors or deplete dopamine levels are often effective in reducing chorea.
The most consistent biochemical finding in conditions like Huntington’s disease is the degeneration of specific inhibitory neurons in the striatum. The loss of these neurons, which normally use the neurotransmitter GABA to dampen signals, releases the brake on the motor system. This structural and chemical disruption leads to the characteristic hyperkinetic movements.
Primary Causes and Associated Conditions
Chorea is not a diagnosis in itself but a symptom that can arise from a wide range of underlying neurological, genetic, metabolic, or autoimmune conditions. The cause dictates whether the condition is temporary or chronic.
The most well-known cause of chronic, progressive chorea in adults is Huntington’s Disease (HD), an inherited neurodegenerative disorder. HD is caused by an expansion of a cytosine-adenine-guanine (CAG) trinucleotide repeat in the HTT gene, leading to the toxic aggregation of the huntingtin protein and progressive loss of brain cells. This genetic cause results in chorea that typically worsens over time, alongside cognitive decline and psychiatric symptoms.
In contrast, Sydenham’s Chorea (SC) is the most frequent cause of acute chorea in children and adolescents. This condition is a complication of rheumatic fever, which follows an untreated infection with Group A Streptococcus bacteria. SC is considered an autoimmune disorder where the immune response mistakenly attacks the basal ganglia, causing the sudden onset of involuntary movements. This form of chorea is usually transient, often resolving completely, though it may recur.
Acquired forms of chorea can result from external factors or other systemic illnesses. Drug-induced chorea is common, often occurring as a side effect of medications that affect dopamine levels, such as certain psychiatric or anti-seizure drugs. Metabolic or endocrine imbalances, such as hyperthyroidism or nonketotic hyperglycemia, can also trigger chorea. This type often resolves once the underlying systemic condition is treated.
Approaches to Managing Chorea Symptoms
The primary goal in managing chorea is to identify and treat the underlying cause, as this may lead to a reduction or complete resolution of the involuntary movements. For instance, in Sydenham’s chorea, treating the underlying streptococcal infection and managing the autoimmune response with medications like corticosteroids can shorten the course of the disorder.
When the underlying cause is chronic, such as Huntington’s disease, treatment focuses on alleviating the severity of the movements to improve function and quality of life. Pharmacological management often targets the overactive dopaminergic pathways in the brain. Medications known as dopamine-depleting agents work by reducing the amount of dopamine available in the brain’s synapses.
Alternatively, some medications act by blocking dopamine receptors, reducing the signal transmission that generates the involuntary movements. These symptomatic treatments, while not curing the underlying condition, can significantly reduce the amplitude and frequency of the chorea. Non-pharmacological support is also important for patient safety and independence. Physical and occupational therapy can help patients maintain mobility, address balance issues, and develop strategies to compensate for the involuntary movements during daily tasks.