• movement disorders
• parkinsonism
• tremor
• dystonia
• chorea
• myoclonus

• CRPS: compound regional pain syndrome
• EEG: electroencephalogram
• EMG: electromyelogram
• GTS: Gilles de la Tourette syndrome
• PED: paroxysmal exercise–induced dyskinesia
• PKC/PKD: paroxysmal kinesigenic choreoathetosis/ dyskinesias
• PNKD: paroxysmal non-kinesigenic dyskinesia
• SPECT: single photon emission computed tomography

The hotch potch of miscellaneous and largely unclassified phenomena which comprise a significant and fascinating part of movement disorders are a challenge for neurologists working on the borderlands of psychiatry, sleep disorders, and epilepsy. Many of these conditions acquired exotic names like “Dubini's electric chorea” and “the variable chorea of Brissaud” that are no longer acknowledged, and the historical conflict between neurological and psychiatric models continues to cause confusion. Where does a complex tic end and a compulsion begin? What about catalepsy and akinetic mutism? Are akathisia, habitual manipulations of the body (for example, trichotillomania), and stereotypies linked biologically?

Progress has been made, nonetheless, and many of these odd movements are now recognised to be symptoms of neurological and systemic disorders:

• oculomasticatory myorhythmia is virtually diagnostic of Whipple's disease

• bizarre nocturnal movements including dystonia, stereotypies, chorea, and even vocalisations are increasingly recognised as a presentation of medial frontal seizures; autosomal dominant families with mutations of the neuronal nicotinic acetylcholine receptor gene on chromosomes 20q and 15 respectively have been reported.

• Ekbom's syndrome has become de rigeur as a subject of consequence for neurologists following the demonstration that dopamine receptor agonists may be remarkably effective

Some classic neurological disorders can present with an uncharacteristic abnormal movement:

• the Huntington mutation has been found in middle aged patients presenting with Parkinson's syndrome and cases with generalised myoclonus have been described

• chorea–acanthocytosis may present with parkinsonism

• the spinocerebellar ataxias and ataxia–telangiectasia with dystonia or chorea

• Wilson's disease can present with stereotypies

• Freidreich's ataxia occasionally presents with myoclonus or chorea.

Few neurologists would now label spasmodic torticollis, musician's tremors, propriospinal myoclonus or startle disease as psychogenic; even tics have a degree of acceptance in most neurological circles. However, one must not shy away from labelling an abnormal movement disorder as psychogenic if the balance of …