Progressive neurodegenerative movement disorder from nigrostriatal dopamine loss.
Also known as: PD, Parkinson's disease, idiopathic parkinsonism
Overview
Progressive neurodegenerative disorder characterized by the cardinal motor features of bradykinesia plus rest tremor and/or rigidity, caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta with alpha-synuclein aggregation (Lewy bodies).
Epidemiology
Second most common neurodegenerative disease after Alzheimer disease. Affects ~1% of adults over 60. Mean age of onset ~60; men slightly more affected than women.
Try two board-style Parkinson Disease questions
Real questions from the FirstPassPA bank, with the full explanation. Pick an answer — no signup, no email.
Question 1NeurologyMedium
A 68-year-old man develops an asymmetric resting tremor, bradykinesia, and cogwheel rigidity over the past year. He is started on levodopa/carbidopa with marked symptomatic improvement. Loss of dopaminergic neurons in which of the following structures best explains his symptoms?
ASubstantia nigra pars compacta
BNucleus basalis of Meynert
CSubthalamic nucleus
DVentral tegmental area
ELocus coeruleus
Reveal answer & full explanation
Correct answer: A — Substantia nigra pars compacta
ASubstantia nigra pars compacta✓
BNucleus basalis of Meynert
CSubthalamic nucleus
DVentral tegmental area
ELocus coeruleus
Why Substantia nigra pars compacta is correct
Parkinson disease results from degeneration of dopaminergic neurons in the substantia nigra pars compacta, reducing dopamine output to the striatum via the nigrostriatal pathway and producing the cardinal motor features.
The marked response to levodopa/carbidopa confirms a dopamine-deficient nigrostriatal circuit.
Why the others are wrong
Nucleus basalis of Meynert — cholinergic nucleus that degenerates in Alzheimer disease, producing memory loss rather than parkinsonism (confused-with another neurodegenerative pathway).
Locus coeruleus — the principal noradrenergic nucleus; its loss is implicated in mood and arousal changes, not the dopaminergic motor deficit (buzzword-matching a brainstem nucleus).
Ventral tegmental area — gives rise to the mesolimbic and mesocortical dopamine pathways involved in reward and cognition, not the nigrostriatal motor pathway (anchoring on 'dopamine' without localizing).
Subthalamic nucleus — the glutamatergic subthalamic nucleus is a familiar Parkinson disease structure because it becomes overactive when nigral dopamine is lost and is a standard deep brain stimulation target, but it contains no dopaminergic neurons and is not the site of neuronal loss; a focal lesion produces contralateral hemiballismus (confused-with the deep brain stimulation target).
Question 2NeurologyMedium
A 68-year-old man with a 6-year history of Parkinson's disease treated with carbidopa-levodopa develops new visual hallucinations and paranoid delusions. His motor symptoms remain well controlled, and reducing dopaminergic medications and reviewing his other drugs have not relieved the psychosis. Which of the following antipsychotic agents is the safest choice for this patient?
AOlanzapine
BHaloperidol
CRisperidone
DQuetiapine
EAripiprazole
Reveal answer & full explanation
Correct answer: D — Quetiapine
AOlanzapine
BHaloperidol
CRisperidone
DQuetiapine✓
EAripiprazole
Why Quetiapine is correct
Psychosis in Parkinson's disease requires an antipsychotic that does not block striatal dopamine and worsen motor function
Quetiapine has very low D2 affinity and is the practical first choice because it does not require the hematologic monitoring that clozapine does
It controls hallucinations and delusions while preserving the motor benefit of carbidopa-levodopa
Clozapine and pimavanserin are the other agents considered safe in Parkinson's disease psychosis
Why the others are wrong
Olanzapine — has meaningful D2 blockade and worsens parkinsonism (confused-with-a-safe-atypical)
Risperidone — a potent D2 antagonist that reliably aggravates motor symptoms (confused-with-a-safe-atypical)
Haloperidol — a typical antipsychotic with strong dopamine blockade that markedly worsens parkinsonism (anchoring on a familiar antipsychotic)
Aripiprazole — a D2 partial agonist, which makes it sound dopamine-sparing, but in Parkinson's disease psychosis it has worsened motor function and been poorly tolerated, so it is not among the agents considered safe (mistaking partial agonism for motor safety)
That's 2. Get 7,700+ more.
Unlock the full FirstPassPA bank: 7,700+ board-style questions, flashcards, and an AI tutor that explains every answer. Your 7-day free trial includes everything, and there's no credit card required.
You've read your 2 free diagnosis previews. Create your free account to unlock the full Parkinson Disease outline — plus all 514 diagnoses, 7,700+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Progressive loss of dopaminergic neurons in the substantia nigra pars compacta reduces dopaminergic input to the striatum. The resulting imbalance of the direct and indirect basal ganglia pathways produces a hypokinetic movement disorder. Intracellular alpha-synuclein aggregates (Lewy bodies and Lewy neurites) are the pathologic hallmark and also affect the brainstem, olfactory bulb, and autonomic neurons (explaining hyposmia, REM behavior disorder, and dysautonomia, which often precede motor symptoms).
Asymmetric rest tremor, abolished with voluntary action
Cogwheel rigidity at the wrist (enhanced by contralateral activation)
Bradykinesia on finger taps, hand opening/closing, foot taps — decrement in amplitude and speed
Stooped posture, reduced arm swing
Pull test: retropulsion with multiple corrective steps or fall — indicates postural instability
Glabellar tap sign (Myerson's sign): persistent blinking on repeated tapping
Classic findings
Asymmetric rest tremor + bradykinesia + cogwheel rigidity with excellent response to levodopa is highly suggestive.
Differential diagnosis
Essential tremor — Bilateral action/postural tremor of hands and head, family history, improves with alcohol, no bradykinesia or rigidity
Drug-induced parkinsonism — Antipsychotics (typical and atypical), metoclopramide, prochlorperazine; usually symmetric, tremor less prominent (rest tremor can occur), resolves weeks-months after offending drug stopped
Multiple system atrophy (MSA) — Parkinsonism + early autonomic failure (orthostasis, urinary), cerebellar signs (MSA-C); poor levodopa response; 'hot cross bun' sign on pons MRI
Progressive supranuclear palsy (PSP) — Early postural instability with backward falls, vertical supranuclear gaze palsy (downgaze first), axial rigidity, hummingbird sign on midbrain MRI
Lewy body dementia (DLB) — Dementia precedes or appears within 1 year of parkinsonism; fluctuating cognition, visual hallucinations, REM behavior disorder, neuroleptic sensitivity
Vascular parkinsonism — Lower-body predominant ('lower-half parkinsonism'), gait apraxia, vascular risk factors, white matter disease on MRI, poor levodopa response
Normal pressure hydrocephalus — Magnetic gait, urinary incontinence, cognitive impairment; ventriculomegaly out of proportion to atrophy
Diagnostic workup
Diagnostic criteria
MDS clinical diagnostic criteria: bradykinesia plus rest tremor and/or rigidity; supported by clear levodopa response, levodopa-induced dyskinesia, rest tremor, olfactory loss; red flags suggesting atypical parkinsonism must be absent.
Labs
Largely a clinical diagnosis; labs to exclude mimics: TSH, CBC, BMP, B12
Consider ceruloplasmin in young-onset (<40) to exclude Wilson disease
Imaging
MRI brain — usually normal in PD; helps exclude vascular disease, NPH, atypical parkinsonism
DaTscan (123I-ioflupane SPECT) — shows reduced striatal dopamine transporter binding; differentiates PD/atypical parkinsonism from essential tremor or drug-induced parkinsonism, but does NOT distinguish PD from MSA/PSP/CBD
Levodopa challenge — robust, sustained motor improvement supports PD
Diagnostic algorithm
Feature
Idiopathic PD
MSA
PSP
DLB
Onset symmetry
Asymmetric
Variable
Symmetric
Symmetric
Rest tremor
Prominent
Uncommon
Uncommon
Variable
Early postural instability
No
Yes
Yes (backward falls)
Variable
Autonomic failure
Late
Early, severe
Mild
Variable
Vertical gaze palsy
No
No
Yes (downgaze)
No
Cognitive decline
Late (>1 yr)
Late
Frontal/executive
Early (<1 yr); fluctuating
Visual hallucinations
Late / med-related
Rare
Rare
Early, prominent
Levodopa response
Excellent, sustained
Poor or transient
Poor
Variable; neuroleptic sensitive
Differentiating idiopathic Parkinson disease from atypical parkinsonian syndromes.
Treatment
First-line
Levodopa/carbidopa — most effective symptomatic therapy; carbidopa inhibits peripheral DOPA decarboxylase to reduce nausea and increase central availability; start low (25/100 TID) and titrate
Dopamine agonist — pramipexole, ropinirole, rotigotine (transdermal); levodopa remains the preferred initial dopaminergic therapy at any age (AAN 2021), but an agonist may be chosen first in select patients <60 at high dyskinesia risk; avoid agonists in patients >70 or with impulse control disorder history, cognitive impairment, excessive daytime sleepiness, or hallucinations; watch for impulse control disorders (gambling, hypersexuality, binge eating), somnolence, edema
MAO-B inhibitor — selegiline, rasagiline (safinamide is approved only as an adjunct to levodopa); mild symptomatic benefit, useful as initial monotherapy in mild disease or adjunct for motor fluctuations
Anticholinergic — trihexyphenidyl, benztropine; reserved for tremor-predominant disease in younger patients; avoid in elderly due to cognitive effects
Amantadine — modest benefit for tremor and for levodopa-induced dyskinesia
Second-line / adjunct
Motor fluctuations / wearing-off: shorten levodopa interval, add COMT inhibitor (entacapone, opicapone, tolcapone — monitor LFTs with tolcapone), MAO-B inhibitor, or dopamine agonist
Dyskinesia: reduce individual levodopa doses, add amantadine ER
Advanced disease: deep brain stimulation of subthalamic nucleus or globus pallidus interna (best for patients with levodopa-responsive symptoms but disabling motor fluctuations or dyskinesia and intact cognition)
Levodopa-carbidopa intestinal gel (continuous infusion), apomorphine SC infusion or rescue injections
Dysphagia and aspiration pneumonia (leading cause of death)
Impulse control disorders with dopamine agonists
Neuroleptic malignant-like syndrome with abrupt levodopa withdrawal
PANCE pearls
NEVER abruptly stop levodopa — risk of neuroleptic malignant-like syndrome (parkinsonism-hyperpyrexia syndrome: fever, rigidity, autonomic instability, high CK). Levodopa is a do-not-hold drug: if the patient is NPO, give crushed immediate-release carbidopa-levodopa by NG tube, or a rotigotine patch if there is no enteral route. Treat a crisis by restoring dopaminergic therapy plus cooling and IV fluids (dantrolene is adjunct only); never give haloperidol or metoclopramide.
Asymmetric onset is a key clue — symmetric parkinsonism suggests an atypical or drug-induced cause.
Rest tremor is the most specific sign for idiopathic PD; absence of rest tremor does NOT exclude PD (akinetic-rigid variant).
If a patient develops parkinsonism plus early dementia, hallucinations, or autonomic failure, think Lewy body dementia, MSA, or PSP — NOT idiopathic PD.
Avoid dopamine-blocking antiemetics (metoclopramide, prochlorperazine) — use ondansetron or trimethobenzamide instead.
Avoid first-generation antipsychotics for PD-related psychosis; pimavanserin (5-HT2A inverse agonist) is FDA-approved without worsening motor symptoms.
References
AAN 2021 — Dopaminergic Therapy for Motor Symptoms in Early Parkinson Disease Practice Guideline Summary: A Report of the AAN Guideline Subcommittee (Pringsheim et al., Neurology 2021;97:942-957)
MDS 2015 — MDS Clinical Diagnostic Criteria for Parkinson Disease (Postuma et al., Mov Disord 2015)
EARLYSTIM Trial — Neurostimulation for Parkinson Disease with Early Motor Complications (Schuepbach et al., NEJM 2013)
Practice Neurology questions on FirstPassPA
Turn this outline into retention. 7,700+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.