Klinik, Pathophysiologic und klinische Neurophysiologie der Chorea

Choreatic hyperkinesias are found in a variety of neurodegenerative disorders. In addition, choreatic symptoms may also accompany many generalised immunological, infectious and metabolic diseases or may be sig ns of side effects of prescribed or illicit drugs. A number of clinical scares have been developed enabling the clinician to quantify the degree of the choreatic symptoms. Choreatic hyperkinesias are caused by functional or structural disturbances of the basal ganglia. Based on neuropathological and experimental evidence models of basal ganglia connections have been developed which attribute chorea to a disinhibition of thalamocortical pathways via a loss of inhibitory input from the main basal ganglia output structures. In Huntington's disease the loss of GABAergic fibres from the caudate nucleus to the external pallidal segment is thought to be responsible for the disinhibition of the basal ganglia motor loop. Recently, new findings concerning the efficacy of stereotactic pallidotomy in treating hyperkinetic syndromes have shed some doubt on the validity of current basal ganglia models. It is conceivable that current models will be revised in the near future. Abnormalities in a variety of neurophysiological methods have been reported in patients with choreatic syndromes. Patients with Huntington's disease were found to have reduced amplitudes of early somatosensory evoked potentials, absent cortically mediated long-latency stretch reflexes in small hand muscles, delayed R2 components of the blink reflex as well as a prolonged "silent period" following cortical magnetic stimulation. These abnormalities were not only detected in patients with the classical hyperkinetic form of the disease but also in patients with the rigid-akinetic Westphal variant as well as in still asymptomatic carriers of the Huntington's disease gene. The characteristic pattern of neurophysiological abnormalities seen in Huntington's disease patients could not be replicated in patients with choreatic syndromes of other etiologies. Clinical neurophysiology in hyperkinetic syndromes is, therefore, not a mere reflection of the patient's symptomatology but gives clues to the underlying pathophysiological process.