Bradley's dyskinesia
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Dyskinesia — Bradley and Daroff's Neurology in Clinical Practice
Dyskinesia refers broadly to abnormal, involuntary movements. Bradley and Daroff covers two major categories in depth: Tardive Dyskinesia (drug-induced) and Paroxysmal Dyskinesias (episodic, often genetic).
I. TARDIVE DYSKINESIA (TD)
Classic Tardive Stereotypy
TD is a movement disorder arising from chronic dopamine receptor blockade, most commonly from antipsychotics or antiemetics (e.g., metoclopramide). Key features:
- Requires a minimum of 6 weeks of dopamine receptor blockade (though onset after a single dose has been reported)
- Risk factors: advanced age, female sex, affective disorder, edentulousness, diabetes mellitus, prior CNS injury
- Classic appearance: repetitive, stereotypic orobuccolingual dyskinesias — chewing movements of the mouth, tongue, and lower face; upper face is typically spared
- Other hyperkinetic manifestations: chorea, akathisia, dystonia, tics, myoclonus, pelvic thrusting, respiratory dyskinesia, limb chorea
Pathophysiology:
- Incompletely understood; involves potent D2 receptor blockade
- Proposed mechanisms: denervation supersensitivity of postsynaptic dopamine receptors, oxidative stress, GABA insufficiency, striatal apoptosis
- Genetic susceptibility: polymorphisms in dopamine D3 receptor gene and 5-HT2C serotonin receptor gene
Management:
- Primary intervention: prevention (use atypical antipsychotics where possible; monitor regularly)
- Discontinue offending drug if possible
- Mild TD: benzodiazepines or baclofen
- FDA-approved treatments: deutetrabenazine and valbenazine (VMAT2 inhibitors)
Tardive Dystonia
A distinct subtype from classic TD:
| Feature | Classic TD | Tardive Dystonia |
|---|---|---|
| Demographics | Elderly women | Young men |
| Onset | After 6 weeks+ | Median 5.1 years exposure |
| Distribution | Orofacial | Focal/segmental or truncal (opisthotonic posturing + pronation of arms) |
| Recovery | Common after drug withdrawal | Less common; may improve over 5 years |
- Typical presentation: truncal dystonia with opisthotonic posturing in a young man, with arm pronation and elbow extension
- Age–distribution relationship: trunk/legs in younger; face/jaw/neck in older
- More retrocollis and anterocollis than primary focal dystonia
Treatment: Prevention first; then VMAT2 inhibitors, anticholinergics, benzodiazepines, baclofen, botulinum toxin (especially for focal dystonia such as blepharospasm or cervical dystonia), intrathecal baclofen
II. PAROXYSMAL DYSKINESIAS
Rare syndromes with recurrent episodic attacks of involuntary movements (dystonia, chorea, athetosis, ballism, or mixed). Most are autosomal dominant.
Comparison Table
| Feature | Paroxysmal Kinesigenic Dyskinesia (PKD) | Paroxysmal Non-kinesigenic Dyskinesia (PNKD) | Paroxysmal Exercise-induced Dyskinesia (PED) | Paroxysmal Hypnogenic Dyskinesia (PHD) |
|---|---|---|---|---|
| Trigger | Sudden movement, startle, acceleration | Alcohol, caffeine, stress, fatigue | Prolonged exercise (after 15–20 min) | Sleep |
| Duration | Seconds to 5 min | 2 min to 4 hours | 5 min to 2 hours | 30–50 min |
| Frequency | 1/month to 100/day | Few/week to rare lifetime events | Few/month | Few/year to nightly |
| Phenomenology | Choreoathetosis + dystonia | Dystonia ± choreoathetosis | Predominantly lower limb dystonia | Dystonia, chorea, ballism |
| Gender M:F | 4:1 | 2:1 | 2:3 | 7:3 |
| Gene | PRRT2 (16p11.2) | PNKD/MR1 (chr 2q35); SLC2A1 (chr 1) | SLC2A1/GLUT1 (1p35) | CHRNA4, CHRNB2 |
| Treatment | Anticonvulsants (carbamazepine, phenytoin) | Trigger avoidance; clonazepam | Trigger avoidance; ketogenic diet | Anticonvulsants |
| Inheritance | AD | AD | AD | Usually sporadic |
Key Points per Subtype
PKD
- PRRT2 gene → also causes benign familial infantile seizures
- PRRT2 involved in neurotransmitter release and synaptic vesicle fusion
- Dramatically responsive to carbamazepine — a diagnostic and therapeutic clue
PNKD
- PNKD protein is a novel synaptic protein regulating exocytosis
- Pathological mechanism: BK-channel hyperactivation → abnormal dopamine signaling via the indirect striatal pathway
- Ethanol activates BK channels, explaining alcohol as a trigger
PED
- GLUT1 mutation → impaired glucose transport into the brain; ketogenic diet bypasses this by providing alternative fuel
- Attacks begin after sustained exercise (not immediately), distinguishing from PKD
- Some SLC2A1 mutations cause more severe phenotypes including cognitive dysfunction and microcephaly
PHD
- Nocturnal attacks; may represent a form of frontal lobe epilepsy
Unifying Theme
A single gene mutation (e.g., SLC2A1) can produce phenotypic heterogeneity — ranging across paroxysmal dyskinesia, epilepsy, and cognitive dysfunction — illustrating that paroxysmal dyskinesias and certain epilepsies share an overlapping genetic substrate.
Source: Bradley and Daroff's Neurology in Clinical Practice, chapters on Hyperkinetic Movement Disorders and Inherited Neuronal Channelopathies
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