IM19.1-8 | Movement Disorders — Glossary

A 12-item clinician-administered rating scale used to assess the severity and distribution of abnormal involuntary movements, particularly tardive dyskinesia; covers orofacial movements, extremity movements, and trunk movements, each scored 0–4; also includes global severity, patient incapacitation, and patient awareness items.

An antiparkinson drug with multiple mechanisms (weak dopamine releaser, mild anticholinergic, NMDA glutamate receptor antagonist); primary current clinical use: reducing levodopa-induced peak-dose dyskinesias via NMDA antagonism; dose 100 mg twice daily (reduce in CKD); side effects include livedo reticularis, ankle oedema, and confusion.

Drugs blocking muscarinic M1 receptors in the striatum to correct relative cholinergic excess in parkinsonism; examples: trihexyphenidyl (benzhexol), procyclidine; effective for tremor; absolutely avoided in patients over 70 and those with cognitive impairment due to central anticholinergic side effects (confusion, hallucinations, delirium).

A group of subcortical nuclei (caudate nucleus, putamen, globus pallidus, subthalamic nucleus, substantia nigra) that modulate cortical motor output via cortico-striato-thalamo-cortical loops; dysfunction causes movement disorders.

Slowness of voluntary movement with reduced amplitude and fatiguing; the cardinal feature required for the diagnosis of parkinsonism; distinct from weakness, as strength is relatively preserved.

A peripheral aromatic amino acid decarboxylase inhibitor that cannot cross the blood-brain barrier; combined with levodopa in fixed-ratio preparations (Sinemet, co-careldopa) to prevent peripheral conversion of L-DOPA to dopamine outside the brain, reducing peripheral dopaminergic side effects and increasing the fraction of L-DOPA reaching the brain.

Random, irregular, non-repetitive, flowing involuntary movements that appear to move unpredictably from one body part to another; arises from reduced GPi output and thalamic disinhibition; causes include Huntington's disease, Sydenham's chorea, and drug-induced states.

A form of extrapyramidal rigidity in which resistance to passive movement is felt as a series of catch-and-release sensations (like a ratchet) at the wrist or elbow; caused by tremor superimposed on lead-pipe rigidity; classic in Parkinson's disease.

Catechol-O-methyltransferase inhibitor; examples: entacapone (200 mg with each levodopa dose), opicapone (50 mg once daily at bedtime); extends levodopa plasma half-life and reduces wearing-off; only effective in combination with levodopa/carbidopa; side effects include diarrhoea and harmless orange urine discolouration.

Dopamine transporter single-photon emission computed tomography using ioflupane-123I; measures presynaptic dopaminergic terminal integrity in the striatum; abnormal (reduced uptake) in PD and Parkinson-plus syndromes; normal in drug-induced parkinsonism and essential tremor; the key investigation for distinguishing presynaptic dopaminergic deficit from drug-blocked postsynaptic D2 receptors.

A neurosurgical procedure in which high-frequency electrical stimulation is delivered via implanted electrodes to specific basal ganglia targets; STN or GPi for advanced Parkinson's disease; GPi for dystonia; VIM thalamus for essential tremor.

A three-part clinical synthesis specifying: (1) anatomical location of dysfunction (e.g., nigrostriatal pathway, striatum, STN, cerebellum), (2) nature of the pathological process (neurodegenerative, vascular, toxic, autoimmune, metabolic, genetic, functional), and (3) probable aetiology with ranked differential; guides the investigation plan.

The basal ganglia pathway: Cortex → Striatum → GPi/SNr (GABAergic, inhibitory); activation disinhibits the thalamus and facilitates movement; reinforced by dopamine acting on D1 receptors.

A class of antiparkinson drugs that directly stimulate postsynaptic D2/D3 dopamine receptors in the striatum; examples include pramipexole and ropinirole (oral) and rotigotine (transdermal patch); longer half-life than levodopa reduces wearing-off; risk of impulse control disorders (D3 mesolimbic effect) and sudden sleep attacks.

A presynaptic reuptake transporter on nigrostriatal dopaminergic terminals; progressively lost in PD as terminals degenerate; the molecular target for DAT-SPECT radioligands; not affected by postsynaptic-acting drugs (levodopa, dopamine agonists) — DAT-SPECT remains interpretable in treated PD patients.

Parkinsonism caused by dopamine receptor-blocking agents (antipsychotics, metoclopramide, domperidone, flunarizine, cinnarizine), typically presenting symmetrically (bilateral from onset), occurring within weeks to months of drug initiation, and potentially reversible after drug withdrawal; may be clinically indistinguishable from idiopathic PD acutely.

Sustained or intermittent muscle contractions causing abnormal, repetitive twisting movements or postures; often action-induced; may be relieved by sensory tricks (geste antagoniste); focal forms treated with botulinum toxin; generalised forms may require anticholinergics or DBS.

The most common movement disorder in adults; postural and/or kinetic tremor, bilateral, 6–12 Hz; often familial (autosomal dominant); suppressed by alcohol; treated with propranolol or primidone as first-line; DBS of VIM thalamus for refractory cases.

MRI finding in Wilson's disease: on axial T2-weighted MRI through the midbrain, T2 hyperintensity in the midbrain tegmentum surrounding the normally T2-hypointense red nucleus, creating an appearance resembling the face of a panda; supportive of neurological Wilson's disease.

Progressive decrease in speed and amplitude of repetitive voluntary movements on sustained performance (e.g., finger tapping), specifically indicating bradykinesia from nigrostriatal dopaminergic pathway dysfunction; a key discriminator from cerebellar irregularity (which does not systematically fatigue).

A sudden, brief episode of inability to initiate or continue walking despite the intention to do so, as if the feet are stuck to the floor; a feature of advanced Parkinson's disease and progressive supranuclear palsy; associated with falls; triggered by doorways, turns, and narrow spaces.

A clinical technique to sensitise the detection of subtle extrapyramidal rigidity: the patient performs a repetitive voluntary motor task with the contralateral limb (e.g., opening and closing the other hand) while the examiner assesses tone in the ipsilateral wrist by passive rotation, revealing subtle cogwheeling not apparent at rest.

A sensory trick in which touching a specific part of the body (e.g., touching the chin or cheek in cervical dystonia) transiently relieves the dystonic posture or movement; the mechanism involves abnormal sensory-motor integration in dystonia; specific to dystonia and not seen in other movement disorders.

Violent, large-amplitude, flinging involuntary movements of the proximal limbs on one side of the body; caused by a lesion in the contralateral subthalamic nucleus (STN), resulting in loss of STN excitation of GPi and thalamic disinhibition.

A simple staging scale for Parkinson's disease severity: Stage 1 (unilateral disease), Stage 2 (bilateral without balance impairment), Stage 3 (bilateral with mild balance impairment but independent), Stage 4 (severe disability, still able to walk), Stage 5 (wheelchair-bound or bedridden); widely used but less sensitive to change than the MDS-UPDRS.

MRI finding in multiple system atrophy (MSA): cruciform T2 signal hyperintensity in the pons reflecting degeneration of transverse pontocerebellar fibres and pontine nuclei with preservation of corticospinal tracts; characteristic of the cerebellar variant MSA-C.

MRI finding in progressive supranuclear palsy (PSP): selective midbrain atrophy with preserved pontine size on sagittal T1 MRI, creating a profile resembling a hummingbird (small midbrain beak, large pontine body); supports the radiological diagnosis of PSP.

Autosomal dominant neurodegenerative disorder caused by CAG trinucleotide repeat expansion in the HTT gene; presents with progressive chorea, psychiatric symptoms, and cognitive decline; no disease-modifying treatment; chorea suppressed symptomatically with tetrabenazine.

A class of behavioural side effects of dopaminergic therapy (particularly dopamine agonists), including gambling disorder, hypersexuality, binge eating, and compulsive shopping; mediated by D3 receptor stimulation in the mesolimbic dopamine system; require active screening at every clinic review; managed by dose reduction or switching from dopamine agonist to levodopa.

The basal ganglia pathway: Cortex → Striatum → GPe → STN → GPi/SNr; activation increases GPi inhibitory output, suppressing thalamic activity and movement; inhibited by dopamine acting on D2 receptors.

Tremor that increases in amplitude as a limb approaches a target during voluntary movement (positive finger-nose test); implicates cerebellar pathway dysfunction; not a feature of basal ganglia disease.

Golden-brown rings at the peripheral cornea (Descemet's membrane) visible on slit-lamp examination; caused by copper deposition; present in virtually all patients with neurological Wilson's disease; a key diagnostic finding.

Uniform, velocity-independent resistance to passive limb movement throughout the full range of motion, in contrast to spastic resistance (velocity-dependent, clasp-knife); a cardinal feature of extrapyramidal (basal ganglia) disease.

A mottled, net-like bluish-purple discolouration of the skin, typically over the legs and lower trunk; a common, benign, dose-dependent side effect of amantadine; also a feature of vasculitis and some systemic disorders; reversible on dose reduction or drug discontinuation.

The carrier protein responsible for intestinal absorption and blood-brain barrier transport of levodopa; shared by dietary branched-chain and aromatic amino acids; competition from high-protein meals reduces L-DOPA brain delivery, contributing to wearing-off in patients who take levodopa with protein-rich food.

Selective inhibitor of monoamine oxidase type B, the primary enzyme catabolising striatal dopamine; examples: selegiline (5–10 mg/day) and rasagiline (1 mg/day); increases intrasynaptic dopamine levels; used as early monotherapy or adjunct to levodopa; dangerous interaction with pethidine (absolute contraindication — serotonin syndrome) and caution with SSRIs/SNRIs.

The standard validated instrument for comprehensive assessment of Parkinson's disease, comprising four parts: Part I (non-motor daily living), Part II (motor daily living, patient-reported), Part III (motor examination, clinician-rated, 18 items scored 0–4), and Part IV (motor complications including dyskinesias and OFF states).

Meta-iodobenzylguanidine myocardial scintigraphy; measures cardiac sympathetic nerve terminal integrity; reduced myocardial MIBG uptake in PD and DLB (early cardiac denervation from Braak stage 1 alpha-synuclein pathology); preserved uptake in early MSA; used to distinguish DLB from MSA.

Progressive decrease in letter size during handwriting, typically with increasing illegibility towards the end of a word or line; caused by bradykinesia and fatiguing of fine motor movements; a characteristic feature of Parkinson's disease detectable on simple bedside handwriting tests.

Irregular, variable gripping force when a patient with chorea grips the examiner's two fingers, producing a rhythmically varying squeeze that reflects the inability to maintain sustained voluntary muscle activation; a bedside sign of chorea (classically described in Huntington's disease and Sydenham's chorea).

A group of neurodegenerative conditions that include parkinsonism (TRAP features) plus additional atypical features not seen in idiopathic PD; includes progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and corticobasal syndrome (CBS); generally have poor levodopa response.

A group of neurodegenerative disorders that include parkinsonism plus additional atypical features: PSP (early falls, vertical supranuclear gaze palsy, axial rigidity), MSA (autonomic failure + parkinsonism and/or cerebellar ataxia), CBS (asymmetric limb apraxia, alien limb, cortical sensory loss), DLB (cognitive fluctuations, visual hallucinations, REM sleep behaviour disorder); all have poor or absent levodopa response.

Involuntary choreiform or dystonic movements occurring at peak plasma levodopa concentrations (~60–90 minutes after dose), reflecting excessive pulsatile dopaminergic stimulation in the setting of diminished nigrostriatal buffering; the most common form of levodopa-induced dyskinesia; managed with amantadine or dose reduction.

Tremor present when a limb is held against gravity (e.g., arms outstretched); absent at rest; characteristic of essential tremor (6–12 Hz) and physiological/enhanced physiological tremor.

A bedside test of postural reflexes: the examiner stands behind the patient and delivers a brisk backward pull on the shoulders after warning the patient; a normal response is 0–1 recovery steps; retropulsion (more than 3 steps or falling) indicates impaired postural stability, corresponding to MDS-UPDRS Part 3 Item 3.12.

The re-appearance of rest tremor after a short latency (typically 2–10 seconds) when a patient with Parkinson's disease holds the arms outstretched in a sustained posture; the tremor has the same frequency as the rest tremor and is distinct from the immediately-present postural tremor of essential tremor.

Tremor present when the affected limb is fully relaxed and supported; absent or markedly reduced during voluntary movement; 4–6 Hz; characteristic of Parkinson's disease; implicates nigrostriatal dopaminergic pathway dysfunction.

A drug interaction syndrome of excess serotonergic neurotransmission; clinical triad: mental status change (confusion/agitation), autonomic instability (hyperthermia, diaphoresis, tachycardia), and neuromuscular abnormality (clonus, myoclonus, hyperreflexia); relevant in PD patients on MAO-B inhibitors exposed to pethidine (absolute contraindication), tramadol, or serotonin reuptake inhibitors.

Inability to maintain sustained tongue protrusion, with the tongue moving irregularly in and out; a bedside sign of chorea affecting orofacial muscles, classically seen in Huntington's disease; used during examination to reveal subtle chorea affecting the tongue.

The collective term for the caudate nucleus and putamen; the primary input nucleus of the basal ganglia, receiving cortical and nigrostriatal dopaminergic projections.

The pigmented midbrain nucleus that projects dopaminergic fibres to the striatum (nigrostriatal pathway); loss of SNc neurons is the defining pathology of Parkinson's disease.

A post-streptococcal, autoimmune chorea associated with acute rheumatic fever; caused by antibodies cross-reacting with basal ganglia neurons (molecular mimicry); self-limited; requires penicillin prophylaxis to prevent recurrence and cardiac damage.

A hyperkinetic movement disorder (predominantly orofacial repetitive movements — lip-smacking, tongue protrusion, facial grimacing) developing after months to years of dopamine receptor-blocking agent (DRBA) exposure; managed by reducing/stopping the offending drug and VMAT2 inhibitors; may be irreversible.

A vesicular monoamine transporter-2 (VMAT2) inhibitor that depletes presynaptic dopamine stores; used to suppress chorea (Huntington's disease, tardive dyskinesia); major side effects include depression, sedation, and parkinsonism.

The cardinal features of parkinsonism: Tremor at rest, Rigidity, Akinesia/bradykinesia, and Postural instability; bradykinesia is the mandatory feature for the diagnosis.

A long-term levodopa complication in which parkinsonism returns predictably before the next scheduled dose; caused by progressive shortening of the beneficial duration of levodopa effect as nigrostriatal dopaminergic buffering capacity is lost; managed by addition of COMT inhibitor, MAO-B inhibitor, or increased dose frequency.

Autosomal recessive disorder of copper transport (ATP7B mutation) with copper accumulation in liver, basal ganglia, and cornea; presents in young adults with movement disorder, psychiatric symptoms, and liver disease; confirmed by low ceruloplasmin + high 24-h urinary copper + KF rings; treated with trientine or D-penicillamine chelation.