Movement disorders other than Parkinson’s disease

Movement disorders are considered in five main categories—dystonia, chorea, tremor, tics, and myoclonus. Each disorder may occur in several diseases, and each may be the sole manifestation of a given neurological disease, but they also may only represent a component of a more widespread disorder.

Movement disorders characteristically involve the basal ganglia and under these circumstances, neuropsychiatric manifestations—often more significant than the disturbed movement—have the greater impact on well-being.

Most treatments for movement disorders are empirical, but with greater understanding of the molecular genetics and the application of functional imaging, a more rational neurochemical basis for several disorders is emerging. Ultimately this greater understanding may lead to the development of effective therapies based on rational principles.

Particular movement disorders

Dystonias—so-called idiopathic torsion dystonia is often inherited as an autosomal dominant trait; other causes include the Dopa-responsive dystonia-Parkinsonism (Segawa’s syndrome), writer’s cramp and oromandibular dystonia (which responds poorly to most drugs).

Chorea—occurs in many conditions and may be a consequence of any treatment for Parkinson’s disease. The most common other cause is Huntington’s disease. Sydenham’s chorea (St Vitus’s dance), for which dopamine D₂ receptor blocking agents may be effective, and neuropsychiatric manifestations are associated with rheumatic fever and other complications of group A streptococcal infections.

Tremor—this includes ‘essential’ tremor, for which several candidate susceptibility gene loci have been identified.

Tics—these may be simple or complex, and arise in numerous disorders. When combined with copralalia and other sudden vocalization, Tourette’s syndrome—a genetic disorder showing autosomal dominant transmission with variable penetrance—is identified. The tics may respond to neuroleptic agents, and the associated obsessive-compulsive behavioural features often benefit from clomipramine (a tricyclic agent) or fluoxetine; deep brain stimulation has been used successfully in severe cases, but is not yet established as a routine treatment.

Myoclonus—this occurs in numerous neurological diseases. It may be solitary and static, as in benign essential myoclonus, or a progressive disease with encephalopathy (progressive myoclonic encephalopathy), and it is also a feature of epilepsy. Static myoclonus after action (Lance–Adam syndrome) may develop after cerebral anoxia.

Miscellaneous movement disorders—these include (1) psychogenic conditions; (2) numerous drug-induced conditions, usually induced by anti-psychotic or anti-emetic drugs; (3) the stiff man syndrome; and (4) restless legs (Ekböm’s) syndrome—a common condition.