Confusable diagnoses · PANCE / PANRE

Parkinson Disease vs Dementia with Lewy Bodies

Written & clinically reviewed by Ryan Busch, PA-C · Updated August 2026 · Report an error

Parkinson Disease and Dementia with Lewy Bodies are easy to mix up on the boards. Here's a side-by-side comparison — presentation, workup, imaging, and first-line treatment — drawn from our full outlines.

Parkinson Disease vs Dementia with Lewy Bodies at a glance

  • Parkinson Disease: Progressive neurodegenerative movement disorder from nigrostriatal dopamine loss.
  • Dementia with Lewy Bodies: Neurodegenerative dementia with fluctuating cognition, recurrent visual hallucinations, parkinsonism, and REM sleep behavior disorder.

Try two board-style questions on Parkinson Disease vs Dementia with Lewy Bodies

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Question 1NeurologyMedium
A 78-year-old male with Parkinson's disease on carbidopa-levodopa for 8 years now has 3-4 hours of good motor function after each dose, followed by return of rigidity and slowness in the 45 minutes before his next scheduled dose. Which of the following is the most appropriate medication adjustment to reduce 'off' time?
  • AAdd entacapone
  • BSwitch to bromocriptine
  • CAdd benztropine
  • DAdd pimavanserin
Reveal answer & full explanation
Correct answer: A — Add entacapone
  • AAdd entacapone✓
  • BSwitch to bromocriptine
  • CAdd benztropine
  • DAdd pimavanserin

Why Add entacapone is correct

  • Levodopa wearing-off (motor fluctuations) is common after 5–10 years of Parkinson's disease (PD) treatment.
  • Entacapone is a catechol-O-methyltransferase (COMT) inhibitor that blocks peripheral levodopa metabolism, thereby extending the effect of each levodopa dose.
  • Opicapone is another COMT inhibitor option.

Why the others are wrong

  • Switch to bromocriptine — Bromocriptine is an older dopamine agonist; switching away from carbidopa-levodopa is not the preferred strategy for wearing-off, and bromocriptine has a less favorable side-effect profile.
  • Add benztropine — An anticholinergic agent used for tremor; it does not address wearing-off and anticholinergics can worsen off-time and cognitive function.
  • Add pimavanserin — A selective serotonin 5-HT2A inverse agonist approved for the hallucinations and delusions of Parkinson disease psychosis; it has no dopaminergic action, so it neither extends each levodopa dose nor shortens off time.

Additional high-yield points

  • Monoamine oxidase B (MAO-B) inhibitors (rasagiline, safinamide) block central dopamine metabolism and are another strategy for wearing-off.
  • Additional strategies include more frequent smaller levodopa doses, dopamine agonists, and subcutaneous apomorphine for rescue.
  • Deep brain stimulation (DBS) is used for refractory motor fluctuations.
Question 2NeurologyMedium
A 74-year-old man is brought in by his wife for 8 months of progressive cognitive decline marked by striking day-to-day fluctuations in alertness and frequent, well-formed visual hallucinations of children in the house. She also reports he acts out his dreams at night, kicking and shouting. On exam he has symmetric bradykinesia and rigidity with mild postural instability. Memory is relatively preserved, but he scores poorly on clock drawing and intersecting pentagons. The hallucinations are increasingly distressing to him. Which of the following is the most appropriate initial management?
  • AStart risperidone
  • BStart donepezil
  • CStart memantine
  • DStart haloperidol
Reveal answer & full explanation
Correct answer: B — Start donepezil
  • AStart risperidone
  • BStart donepezil✓
  • CStart memantine
  • DStart haloperidol

Why Start donepezil is correct

  • This vignette is classic dementia with Lewy bodies (DLB): fluctuating cognition, recurrent well-formed visual hallucinations, REM sleep behavior disorder, and parkinsonism with relatively preserved memory and impaired visuospatial testing (clock draw, pentagons).
  • Cholinesterase inhibitors (donepezil, rivastigmine, galantamine) are first-line. DLB has profound cholinergic deficits and is among the most responsive dementias to these agents, which improve cognition and reduce visual hallucinations.
  • Per McKeith 2017 DLB consensus and AAN guidance, distressing hallucinations are addressed first with a cholinesterase inhibitor and removal of offending drugs before any antipsychotic is considered.

Why the others are wrong

  • Start haloperidol — a typical (high-potency) antipsychotic; strictly avoided in DLB because of severe neuroleptic sensitivity (rigidity, hyperthermia, autonomic instability, death).
  • Start memantine — an NMDA antagonist used only as an adjunct in moderate-to-severe disease; it is not the first-line agent for cognition or hallucinations in DLB, where cholinesterase inhibitors are more effective.
  • Start risperidone — a high-potency D2-blocking antipsychotic that carries the same life-threatening neuroleptic sensitivity risk in DLB; if pharmacotherapy is ever required for psychosis, pimavanserin or low-dose quetiapine/clozapine is preferred.
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Side-by-side comparison

FeatureParkinson DiseaseDementia with Lewy Bodies
At a glanceProgressive neurodegenerative movement disorder from nigrostriatal dopamine loss.Neurodegenerative dementia with fluctuating cognition, recurrent visual hallucinations, parkinsonism, and REM sleep behavior disorder.
Classic presentationAsymmetric rest tremor + bradykinesia + cogwheel rigidity with excellent response to levodopa is highly suggestive.; Motor: rest tremor (typically asymmetric, 4-6 Hz 'pill-rolling'), bradykinesia (slowness initiating and executing movement), rigidity (cogwheel or lead-pipe), postural instability (later); Gait: shuffling, short steps,…Elderly patient with fluctuating cognition + well-formed visual hallucinations + parkinsonism + history of acting out dreams.; Cognitive fluctuations: pronounced day-to-day or hour-to-hour variation in attention, alertness, and coherence; Recurrent visual hallucinations — typically well-formed people or animals, often non-threatening;…
Workup / key labsMDS 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.; Largely a clinical diagnosis; labs to exclude mimics: TSH, CBC, BMP, B12; Consider ceruloplasmin in…McKeith 2017 criteria: dementia + core features (fluctuating cognition, visual hallucinations, RBD, parkinsonism). Probable DLB = ≥2 core features OR 1 core + ≥1 indicative biomarker (DaTscan, MIBG, polysomnography-confirmed RBD).; TSH, B12, syphilis, HIV (reversible cognitive impairment screen); Comprehensive metabolic panel;…
ImagingMRI 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 —…MRI brain — relative sparing of medial temporal lobes (vs prominent hippocampal atrophy in AD); DaTscan SPECT — reduced striatal dopamine transporter uptake (indicative biomarker); FDG-PET — occipital hypometabolism with cingulate island sign; MIBG cardiac scintigraphy — reduced uptake reflecting cardiac sympathetic denervation
First-line treatmentLevodopa/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…Cholinesterase inhibitors — rivastigmine (oral or transdermal), donepezil, galantamine — among the most responsive dementias to these agents; reduce hallucinations and improve cognition; Memantine — adjunct in moderate-severe disease; Carbidopa-levodopa for parkinsonism — start low, titrate slowly; full PD doses risk worsening…

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Full outlines

Parkinson Disease Dementia with Lewy Bodies All 514 diagnoses

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.