Dystonia and chorea are uncommon abnormal movements which can be seen in a wide array of disorders. One quarter of dystonias and essentially all choreas are symptomatic or secondary, the underlying cause being an identifiable neurodegenerative disorder, hereditary metabolic defect, or acquired systemic medical disorder. Dystonia and chorea associated with neurodegenerative or heritable metabolic disorders have been reviewed frequently.1 Here we review the underlying pathogenesis of chorea and dystonia in acquired general medical disorders (table 1), and discuss diagnostic and therapeutic approaches. The most common aetiologies are hypoxia-ischaemia and medications.2-4 Infections and autoimmune and metabolic disorders are less frequent causes. Not uncommonly, a given systemic disorder may induce more than one type of dyskinesia by more than one mechanism.

The areas of the brain associated with particular movement disorders have been determined by cerebral imaging and necropsies of patients, and by animal lesioning studies.5-7 Based on such data, chorea seems to result from hypofunction of the indirect pathway from the putamen to the internal globus pallidus, and dystonia correlates more strongly with hyperfunction of the direct relative to the indirect pathway between the putamen and internal globus pallidus, both resulting in inappropriate disinhibition of thalamic projections to the premotor and motor cortex (figure). Chorea has been most consistently associated with lesions in the caudate nucleus or putamen, resulting in disinhibition of the external globus pallidus. Lesions of the subthalamo-internal pallidal pathway also result in chorea. Associated neurotransmitter abnormalities include deficient striatal GABA-ergic function and striatal cholinergic interneuron activity, and dopaminergic hyperactivity in the nigrostriatal pathway. Dystonia has been correlated with lesions of the contralateral putamen, external globus pallidus, posterior and posterior lateral thalamus, red nucleus, or subthalamic nucleus, or a combination of these structures. The result is decreased activity in the …