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Drug-Induced Movement Disorders

What Do You Need to Know?

Tardive dyskinesia — D2 blocker exposure ≥3 months, oro-buccal-lingual stereotypies, VMAT2 inhibitors (valbenazine, deutetrabenazine)
NMS — lead-pipe rigidity + hyperthermia + AMS + CK elevation; dantrolene + bromocriptine
Serotonin syndrome — clonus (key feature) + agitation + hyperthermia; cyproheptadine
Akathisia — most common acute drug-induced movement disorder; propranolol first-line
Drug-induced parkinsonism — classically bilateral/symmetric with normal DaTscan and often reversible after withdrawal; this is a pattern, not absolute — DIP can also unmask underlying degenerative PD, and DaTscan can be abnormal in those cases
Acute dystonic reaction — hours to days after D2 blocker; IV diphenhydramine or benztropine

🚩 Don’t Miss — Test-Day Priorities

NMS vs serotonin syndrome: NMS = lead-pipe rigidity, hyporeflexia, slow onset (days), after D2 blocker OR levodopa withdrawal; serotonin syndrome = clonus (LE > UE), hyperreflexia, rapid onset (hours), after serotonergic combination — clonus is the single best discriminator.
Drug-induced parkinsonism — typical pattern: symmetric bilateral bradykinesia/rigidity, normal DaTscan (preserved presynaptic dopamine), reversible over weeks–months after stopping offender. Frame as a pattern rather than absolute — DIP can unmask underlying degenerative PD; in those cases DaTscan can be abnormal and parkinsonism may persist or progress.
Anticholinergics: help acute dystonic reaction and tardive dystonia, WORSEN tardive dyskinesia — classic board distinction; avoid in elderly with DIP.
Acute dystonic reaction: young male, hours-days after antipsychotic/metoclopramide/prochlorperazine, oculogyric crisis + torticollis + tongue protrusion → IV/IM diphenhydramine or benztropine.
Tardive dyskinesia treatment: VMAT2 inhibitors — valbenazine and deutetrabenazine are FDA-approved; tetrabenazine off-label; clozapine for refractory psychosis with TD.
Abrupt levodopa/dopamine-agonist withdrawal in PD → NMS-like syndrome — never stop cold; taper slowly.
Dopamine agonist withdrawal syndrome (DAWS): depression, anxiety, dysphoria, drug craving, pain — does NOT respond to levodopa; resume DA agonist and taper more slowly.
Impulse control disorders (gambling, hypersexuality, shopping, binge eating) on pramipexole/ropinirole — ask every PD visit; reduce/withdraw DA agonist gradually.
Lithium toxicity: coarse tremor + ataxia + dysarthria + confusion ± seizures; hemodialysis if severe; chronic toxicity can cause irreversible cerebellar damage (SILENT syndrome).
Akathisia is the most common acute drug-induced movement disorder — subjective inner restlessness + observable pacing; propranolol first-line; do NOT mistake for psychotic agitation and uptitrate antipsychotic.
Drugs that worsen myasthenia gravis: aminoglycosides, fluoroquinolones, macrolides, telithromycin, β-blockers, magnesium, procainamide, quinidine, D-penicillamine, immune checkpoint inhibitors.
Drugs that worsen/cause parkinsonism: antipsychotics (typical > atypical), metoclopramide, prochlorperazine, valproate (especially elderly), amiodarone, lithium, tetrabenazine.

🔍 Buzzwords & Pathognomonic FindingsClinical · Offending drugs · Treatment

Clinical phenotype

Oculogyric crisis + tongue protrusion + torticollis in young male hours after Compazine → acute dystonic reaction
Lead-pipe rigidity + hyperthermia >40°C + AMS + CK >10,000 → NMS
Clonus (LE > UE) + hyperreflexia + diaphoresis + diarrhea + agitation → serotonin syndrome
Oro-buccal-lingual chewing/lip-smacking/tongue-rolling after years on antipsychotic → tardive dyskinesia
Retrocollis + sustained postures after chronic neuroleptic → tardive dystonia
Inner restlessness, can’t sit still, pacing days after starting risperidone → akathisia
Symmetric bilateral bradykinesia/rigidity, NORMAL DaTscan → drug-induced parkinsonism
Coarse postural tremor + ataxia + dysarthria + confusion → lithium toxicity
New-onset gambling/hypersexuality in PD patient → impulse control disorder on DA agonist
Punding, compulsive levodopa use, hypomania in PD → dopamine dysregulation syndrome

Offending drugs / mechanism

Haloperidol, fluphenazine, metoclopramide, prochlorperazine (D2 blockers) → acute dystonia, NMS, akathisia, TD, DIP
SSRI + MAOI / tramadol / linezolid / fentanyl / methylene blue → serotonin syndrome
Abrupt levodopa or DA-agonist withdrawal in PD → NMS-like syndrome / DAWS
Pramipexole, ropinirole, rotigotine → impulse control disorders, DAWS on taper
Lithium, valproate (dose-related), β-agonists, amiodarone, SSRIs, TCAs, theophylline, prednisone → drug-induced action/postural tremor
Valproate (especially elderly), amiodarone, lithium, tetrabenazine → drug-induced parkinsonism
Aminoglycosides, fluoroquinolones, macrolides, β-blockers, magnesium, D-penicillamine, checkpoint inhibitors → worsen myasthenia gravis

Treatment / management pearls

IV/IM diphenhydramine or benztropine → acute dystonic reaction
Stop neuroleptic + IV fluids + cooling + dantrolene + bromocriptine/amantadine → NMS
Stop serotonergic + cyproheptadine + supportive care → serotonin syndrome
Propranolol (first-line), benzodiazepines, mirtazapine → akathisia
Valbenazine or deutetrabenazine (VMAT2 inhibitors) → tardive dyskinesia
Anticholinergics (trihexyphenidyl), botulinum toxin, GPi DBS → tardive dystonia (anticholinergics WORSEN TD)
Withdraw offender + amantadine bridge; avoid anticholinergics in elderly → drug-induced parkinsonism
Discontinue lithium + hemodialysis if severe/≥4 mEq/L or symptomatic → lithium toxicity
Reduce/withdraw DA agonist gradually; screen at every PD visit → impulse control disorders
Resume DA agonist and taper more slowly (does NOT respond to levodopa) → dopamine agonist withdrawal syndrome

Tardive Dyskinesia

Definition & Mechanism

Tardive = “late-onset” — prolonged D2 receptor blocker exposure
Minimum exposure: ≥3 months (or ≥1 month if age >60)
Pathophysiology: Dopamine receptor upregulation/supersensitivity from chronic D2 blockade
Offending agents: Typical > atypical antipsychotics; metoclopramide, prochlorperazine

Clinical Features

Oro-buccal-lingual stereotypies (most common) — chewing, lip smacking, tongue protrusion/rolling
Choreiform movements of limbs/trunk; respiratory dyskinesias
Repetitive and stereotyped (unlike chorea, which is random and flowing)

Risk Factors & Treatment

Risk factors: Older age (strongest), female, longer exposure, higher dose, African American descent
Step 1: Stop/switch offending agent (quetiapine or clozapine — lowest TD risk)
Step 2: VMAT2 inhibitors — valbenazine (FDA-approved, once-daily) or deutetrabenazine (FDA-approved); tetrabenazine (off-label for TD, requires CYP2D6 genotyping at doses >50 mg/day)
May be irreversible; anticholinergics worsen TD — avoid

💎 Board Pearl

Anticholinergics worsen TD but help acute dystonic reactions and tardive dystonia — critical board distinction.
Do NOT abruptly stop the neuroleptic — withdrawal can worsen TD (“withdrawal dyskinesia”).

Tardive Dystonia

Sustained postures (not stereotyped movements); affects younger patients; more disabling, less likely to remit than TD
Retrocollis (backward neck pulling) — characteristic (vs. anterocollis in idiopathic cervical dystonia)
Trunk extension (opisthotonos), limb dystonia; can coexist with TD

Treatment

Anticholinergics (trihexyphenidyl) — helpful (unlike TD where they worsen symptoms)
Botulinum toxin for focal dystonia; DBS (GPi) if refractory; VMAT2 inhibitors may help

💎 Board Pearl

Retrocollis after chronic neuroleptic use = tardive dystonia.
Tardive dystonia responds to anticholinergics; tardive dyskinesia does NOT.

Neuroleptic Malignant Syndrome

Mechanism & Triggers

Central D2 blockade or dopamine withdrawal (abrupt levodopa cessation)
Onset: 24–72 hours (within 2 weeks of drug initiation/dose change); idiosyncratic, not dose-dependent

Classic Tetrad

Lead-pipe rigidity (NOT cogwheel)
Hyperthermia — often >40°C; from muscle rigidity generating heat
Altered mental status — confusion to coma
Autonomic instability — tachycardia, labile BP, diaphoresis

Labs & Treatment

CK markedly elevated (>1,000, often >10,000); leukocytosis; metabolic acidosis; renal failure (myoglobinuria); low serum iron (supportive but non-specific)
Stop offending agent; IV fluids, cooling, ICU monitoring
Dantrolene (ryanodine receptor inhibitor → ↓ sarcoplasmic Ca²⁺ release) + bromocriptine/amantadine (D2 agonists)
Avoid succinylcholine (hyperkalemia risk); mortality 5–10%

💎 Board Pearl

Lead-pipe rigidity + hyperthermia + CK >1,000 + recent antipsychotic change = NMS.
Abrupt levodopa withdrawal in Parkinson patient can trigger NMS — classic board scenario.

Serotonin Syndrome

Triggers

Excess serotonergic activity (5-HT_1A/5-HT_2A); onset hours (<24 hr)
Combinations: SSRI + MAOI (most dangerous), SSRI + tramadol/triptan, SSRI + linezolid (weak MAOI), methylene blue, meperidine + MAOI
Other triggers: dextromethorphan, MDMA, St. John's wort, meperidine, lithium

Classic Triad

Altered mental status — agitation, confusion, restlessness
Autonomic instability — hyperthermia, tachycardia, diaphoresis, diarrhea, mydriasis
Neuromuscular excitation — CLONUS is the key finding (ocular/inducible/spontaneous), hyperreflexia, tremor

Hunter Criteria

Serotonergic agent + one of: spontaneous clonus; inducible clonus + agitation/diaphoresis; ocular clonus + agitation/diaphoresis; tremor + hyperreflexia; temp >38°C + ocular/inducible clonus

Treatment

Stop serotonergic agents; cyproheptadine (5-HT_2A antagonist, oral only)
Benzodiazepines, cooling; avoid antipyretics (muscular, not hypothalamic)
Resolves 24–72 hours after stopping offending agent

💎 Board Pearl

Clonus = serotonin syndrome; lead-pipe rigidity = NMS — the key distinction.
Linezolid + SSRI is a classic board trap (linezolid = weak MAOI).
Onset: serotonin syndrome hours vs. NMS days–weeks.

Drug-Induced Parkinsonism

Dopamine blockers: Typical > atypical antipsychotics; metoclopramide, prochlorperazine (commonly overlooked)
Also valproic acid, lithium, amiodarone, calcium channel blockers (flunarizine, cinnarizine)
VMAT2 inhibitors (tetrabenazine, valbenazine, deutetrabenazine) as a class can cause parkinsonism via presynaptic dopamine depletion
Second most common cause of parkinsonism after idiopathic PD

Clinical Features

Bilateral and symmetric (vs. asymmetric in PD); bradykinesia/rigidity predominate; rest tremor less prominent
Onset weeks to months; may coexist with tardive dyskinesia

Distinguishing from PD

DaTscan typically normal (intact presynaptic neurons) vs. abnormal in PD — but DIP that has unmasked degenerative PD can show an abnormal DaTscan
Temporal drug relationship; usually bilateral and symmetric; often reversible on withdrawal (weeks to 18 months) — persistence or progression after drug withdrawal should raise concern for underlying PD

Clinical Pearl

Always ask about metoclopramide in new parkinsonism — patients forget GI medications.
Normal DaTscan on neuroleptics favors drug-induced parkinsonism over PD; an abnormal DaTscan in a patient on D2 blockers suggests DIP has unmasked an underlying degenerative parkinsonism.

Akathisia

Most common acute drug-induced movement disorder; onset days to weeks after D2 blocker
Subjective inner restlessness; cannot sit still — pacing, rocking, shifting weight
Subjective distress is the hallmark; can be misdiagnosed as psychotic agitation → dose increase → worsening

Treatment

Propranolol (lipophilic β-blocker) — first-line; benzodiazepines; mirtazapine
Switch to quetiapine or clozapine (lower EPS risk); anticholinergics less effective than for acute dystonia

💎 Board Pearl

Akathisia misdiagnosed as agitation → dose increase → worsening — classic board scenario.
Propranolol first-line for akathisia (NOT anticholinergics).

Acute Dystonic Reaction

Onset hours to days after D2 blocker (90% within 5 days)
Risk factors: Young males, high-potency typicals, cocaine use
Oculogyric crisis (sustained upward eye deviation), torticollis, tongue protrusion, trismus, laryngeal dystonia (airway emergency)

Treatment

IV diphenhydramine or IV benztropine — immediate relief
Oral anticholinergic for 48–72 hours; prophylactic benztropine may be considered for high-risk patients (young males on high-potency typicals)

💎 Board Pearl

Oculogyric crisis + young man on haloperidol = acute dystonic reaction → IV diphenhydramine.
Young males = acute dystonic reactions; older females = tardive dyskinesia.

Malignant Hyperthermia

RYR1 mutation (AD); triggered by volatile anesthetics ± succinylcholine
Uncontrolled Ca²⁺ release from sarcoplasmic reticulum → sustained contraction, hypermetabolism
Early signs: Masseter rigidity, rising end-tidal CO₂ (often earliest), rapidly rising temperature
Rhabdomyolysis, hyperkalemia, metabolic acidosis, DIC
Treatment: Dantrolene (ryanodine receptor inhibitor); stop volatile agents; aggressive cooling
Screening: Caffeine-halothane contracture test (gold standard); RYR1 genetic testing

NMS vs Serotonin Syndrome vs Malignant Hyperthermia

Feature	NMS	Serotonin Syndrome	Malignant Hyperthermia
Cause	D2 blockers / dopamine withdrawal	Serotonergic agents	Volatile anesthetics ± succinylcholine
Onset	Days to weeks	Hours	Minutes (intraoperative)
Rigidity	Lead-pipe	Hypertonicity	Generalized
Clonus	Absent	Present (hallmark)	Absent
Reflexes	Normal/decreased	Hyperreflexia	Decreased
Pupils	Normal	Mydriasis	Normal
CK	Markedly elevated	Mild–moderate	Markedly elevated
Treatment	Dantrolene + bromocriptine	Cyproheptadine	Dantrolene
Genetic	None	None	RYR1 (AD)

💎 Board Pearl

Clonus = serotonin syndrome; lead-pipe rigidity = NMS; intraoperative = MH — most tested distinction.
Onset: MH minutes < serotonin syndrome hours < NMS days–weeks.
Dantrolene for NMS and MH; cyproheptadine for serotonin syndrome only.

Drug-Induced Tremor

Common offenders: lithium, valproate, beta-agonists (albuterol), amiodarone, caffeine, SSRIs, tricyclics, theophylline, corticosteroids
Phenomenology: typically postural and kinetic tremor (action tremor), bilateral, symmetric; resembles enhanced physiologic tremor
Onset: dose-related; appears after initiation or dose escalation

Treatment

Dose reduction or discontinuation of offending agent
Propranolol 10–80 mg TID if drug cannot be stopped
Primidone as second-line

Lithium Tremor

Therapeutic levels: fine postural action tremor (most common neurologic side effect; ~25–50% of users)
Toxicity: coarse, irregular tremor ± ataxia, myoclonus, encephalopathy — check level
Treatment: propranolol 10–20 mg TID; reduce lithium dose; ensure euvolemia and stable renal function

Valproate Tremor & Parkinsonism

Postural action tremor in 10–25% of users; dose-dependent
Reversible parkinsonism — insidious onset (months to years), bilateral, symmetric; cognitive slowing/hearing loss may coexist
Both dose-dependent and reversible with discontinuation (weeks to months)

💎 Board Pearl

New bilateral action tremor on lithium at therapeutic level → propranolol; if coarse/irregular → check level (toxicity).
Valproate causes both action tremor and reversible parkinsonism — ask about it in any new bilateral parkinsonism.

Levodopa-Induced Dyskinesia (LID)

Types

Peak-dose dyskinesia (most common) — choreiform, occurs at maximal plasma L-dopa levels (~1 hr post-dose)
Diphasic dyskinesia — ballistic/dystonic movements at beginning and end of dose (as levels rise and fall)
Off-period dystonia — painful dystonia (often early morning foot dystonia) when L-dopa wears off

Risk Factors

Younger age at PD onset, longer disease duration, higher cumulative L-dopa dose, lower body weight, female sex

Treatment

Amantadine — first-line; extended-release amantadine (Gocovri) FDA-approved for LID in PD
Add MAO-B inhibitors (rasagiline, selegiline) and/or COMT inhibitors (entacapone, opicapone) to smooth L-dopa levels
Reduce L-dopa dose and fractionate (smaller, more frequent doses) for peak-dose dyskinesia
DBS (STN or GPi) for refractory LID; continuous L-dopa/carbidopa intestinal gel infusion
Off-period dystonia: increase nighttime L-dopa or add dopamine agonist

💎 Board Pearl

Peak-dose = choreiform; diphasic = ballistic; off = dystonic.
Gocovri (ER amantadine) is the only FDA-approved drug for LID.

Drug-Induced Chorea

Levodopa and dopamine agonists (in PD — peak-dose dyskinesia)
Oral contraceptives (chorea gravidarum-like; resolves with discontinuation)
Stimulants — cocaine (“crack dancing”), amphetamines, methylphenidate
Lithium (especially in toxicity)
Anticonvulsants — phenytoin (acute or chronic), carbamazepine, lamotrigine, gabapentin
Antipsychotics (withdrawal-emergent chorea, tardive chorea)

💎 Board Pearl

New chorea in a young woman on OCPs — consider drug-induced; stop OCP, also rule out APS and SLE.
Phenytoin chorea can occur at therapeutic or toxic levels — classic anticonvulsant cause.

Other Tardive Syndromes

Tardive akathisia — persistent restlessness after chronic D2 blockade; distinguished from acute akathisia by chronicity and persistence after drug withdrawal
Tardive tremor — postural/kinetic tremor emerging during or after chronic neuroleptic exposure
Tardive tics — motor and/or vocal tics resembling Tourette syndrome after chronic D2 blockade
All VMAT2-responsive — valbenazine, deutetrabenazine, or tetrabenazine

💎 Board Pearl

Any persistent hyperkinetic movement emerging after ≥3 months of D2 blocker = consider tardive syndrome → VMAT2 inhibitor.

References

Caroff SN, Campbell EC. Drug-induced extrapyramidal syndromes. Psychiatr Clin North Am. 2016;39(3):391-411.
Hauser RA, et al. KINECT 3: valbenazine for tardive dyskinesia. Am J Psychiatry. 2017;174(5):476-484.
Fernandez HH, et al. Deutetrabenazine for tardive dyskinesia (AIM-TD). Neurology. 2017;88(21):2003-2010.
Tse L, et al. Neuroleptic malignant syndrome: a clinically oriented review. Curr Neuropharmacol. 2015;13(3):395-406.
Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005;352(11):1112-1120.
Shin HW, Chung SJ. Drug-induced parkinsonism. J Clin Neurol. 2012;8(1):15-21.
Litman RS, Rosenberg H. Malignant hyperthermia: update on susceptibility testing. JAMA. 2005;293(23):2918-2924.

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