An involuntary, irregular, jerking movement affecting limb and axial muscle groups. These movements are suppressed with difficulty and are incorporated into voluntary gestures resulting in a 'semipurposeful' appearance, e.g. crossing and uncrossing of legs. Causes of chorea Hereditary: - Huntington's disease
- Benign chorea Drugs: - Antiparkinsonian drugs
- oral contraceptives Toxins: - alcohol
- carbon monoxide poisoning Infections: - Sydenham's chorea
— encephalitis HUNTINGTON'S DISEASE This is an autosomal dominant disorder with onset in middle life and progression to death within 10-12 years. Parents of either sex can transmit and penetrance is complete.
It may occur in young persons (juvenile form); here chorea is less apparent and negative symptoms (rigidity) predominate. Pathology
Neuronal loss in the striatum is associated with a reduction in projections to other basal ganglia structures. In addition, cells of the deep layers of the frontal and parietal cortex are lost (corticostriatal projections). The neurochemical basis of this disorder involves deficiency of gamma aminobutyric acid (GABA) and acetylcholine with reduced activity of enzymes glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT). Symptoms and signs
Chorea - may be the initial symptom. This progressess from mere fidgetiness to gross involuntary movements which interrupt voluntary movement and make feeding and walking impossible. Dementia - this is of a subcortical type (see page 122).
Behavioural disturbance - personality change, affective disorders and psychosis occur. Hypotonicity often accompanies fidgety, choreiform movements.
Primitive reflexes - grasp, pout and palmomental - are usually elicited. Eye movements are disturbed with impersistence of gaze.
On clinical grounds with a family history (although true parents may be unknown, or knowledge of illness suppressed). Distinguish from benign hereditary chorea in which intellect is preserved. Exclude senile chorea by older age of onset and absence of dementia. CT scanning may demonstrate atrophy of the caudate nucleus. MRI shows an increase in the T2 signal in the caudate nucleus. Prediction of disease
The Huntington mutation is a tribucleotide repeat on chromosome 4. Identifying this locus provides a reliable method of detecting the disease. Presymptomatic testing is now available in many centres. These tests raise ethical issues but also the possibility of early neuroprotective therapy (NMDA receptor antagonists).
Treatment Phenothiazines, haloperidol or tetrabenazine, may control the movements in the preliminary stages. 355
Metabolic: - Hyperthyroidism
- Hypocalcaemia Immunological: - Systemic lupus erythematosus
- Polyarteritis nodosa Miscellaneous: - Chorea gravidarum
- Polycythaemia rubia vera
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