The chronic administration of phenothiazine drugs or haloperidol (or an idiosyncratic reaction to these drugs) is a common cause of extrapyramidal movement disorders of all types, including chorea; these may become manifest during use of the drug or in a delayed “tardive” fashion, as already mentioned. The newer antipsychosis drugs (the atypical neuroleptics) have been less frequently associated with the problems. Excess dopamine administration in advanced Parkinson disease is perhaps the most common cause of a choreiform dyskinesia in neurologic practice, but the movements tend to be more complex and continuous than those seen in chorea. The use of phenytoin or other anticonvulsant drugs may cause chorea in sensitive individuals. A transitory chorea may occur in the course of an acute metabolic derangement, mainly with hyperosmolar hyperglycemia, hypoglycemia, or hyponatremia, and with the inhalation of crack cocaine.
Rarely, chorea complicates hyperthyroidism, polycythemia vera, lupus erythematosus or some forms of cerebral arteritis. AIDS has emerged as a cause of a few cases of subacute progressive movement disorders that are initially asymmetrical. The usual associations in AIDS have been with focal lesions in or near basal ganglionic structures such as toxoplasmosis, progressive multifocal leukoencephalopathy, and lymphoma, but a number of instances of chorea are not explained by any of these focal lesions. A number of rare paroxysmal kinesigenic disorders, discussed later in this chapter, may have a choreic component.
Chorea may be limited to one side of the body (hemichorea). When the involuntary movements involve proximal limb muscles and are of wide range and flinging in nature, the condition is called hemiballismus (see further on under that heading). A cerebral infarction is the usual cause of both of these disorders.
The review by Piccolo and colleagues puts the frequency of the various causes of chorea in perspective. Of consecutive neurologic admissions to two general hospitals they identified 23 cases of chorea, of which 5 were drug induced, 5 were AIDS related, and 6 were caused by stroke. Sydenham chorea and arteritis were each found in 1 case. In 4 cases no cause could be determined, and 1 proved to be Huntington disease.
The precise anatomic basis of chorea is often uncertain or at least inconsistent. Transient chorea or ballismus arises from infarctions in any part of the striatum, particularly in the caudate, on the side opposite to the movement. In Huntington chorea, there are obvious lesions in the caudate nucleus and putamen. Yet one often observes vascular lesions in these parts without chorea. The localization of lesions in Sydenham chorea and other choreic diseases has not been determined beyond a generalized disturbance in the striatum, which is evident on some imaging studies. It is of interest that in instances of chorea related to acute metabolic disturbances, there are sometimes small infarctions in the basal ganglia or metabolic changes in the lenticular nucleus, as shown by imaging studies. One suspects from their close clinical similarity that chorea and hemiballismus (see below) relate to disorders of the same system of neurons.