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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Core features: fluctuating cognition with pronounced attention variation, recurrent well-formed visual hallucinations, and spontaneous parkinsonism
- REM sleep behaviour disorder (acting out dreams) may precede cognitive symptoms by years
- EXTREME sensitivity to antipsychotics — can cause severe parkinsonism, neuroleptic malignant syndrome, and death
- Treatment: AChEIs (donepezil or rivastigmine) are first-line — beneficial for cognition, hallucinations, and behaviour
- DaTSCAN shows reduced dopamine transporter uptake (distinguishes from AD)
Overview
Dementia with Lewy bodies (DLB) is the third most common cause of dementia (~10–15%). It is caused by alpha-synuclein inclusions (Lewy bodies) in cortical and subcortical neurones, overlapping pathologically with Parkinson's disease dementia (PDD). The distinction is temporal: if dementia precedes or develops within 1 year of parkinsonism = DLB; if parkinsonism precedes dementia by >1 year = PDD. Core clinical features are fluctuating cognition, visual hallucinations, and parkinsonism. The 1-year rule helps differentiate DLB from PDD but is somewhat arbitrary.
Epidemiology
DLB accounts for approximately 10–15% of dementia cases. It typically presents after age 65 and is more common in men. Risk factors overlap with AD and PD. Alpha-synucleinopathies (DLB, PDD, PD) exist on a spectrum. DLB is often under-recognised and misdiagnosed as AD or delirium.
Clinical Features
Symptoms
Fluctuating cognition: pronounced variation in attention and alertness — "good days and bad days" with periods of near-normal function alternating with severe confusion
Recurrent detailed visual hallucinations: often well-formed, vivid (people, animals) — may not be distressing initially
Parkinsonism: rigidity and bradykinesia predominate over tremor (contrast with PD)
REM sleep behaviour disorder: vivid dreams acted out physically (punching, kicking during sleep)
Recurrent falls and syncope
Autonomic dysfunction: postural hypotension, constipation, urinary incontinence
Depression and apathy
Signs
Fluctuating attention and arousal (may be mistaken for delirium)
Parkinsonism: rigidity, bradykinesia, shuffling gait (tremor less prominent than PD)
Postural hypotension
Cognitive profile: visuospatial and executive dysfunction > memory loss (clock drawing test markedly impaired)
Investigations
First-line
Clinical assessment and cognitive testingACE-III with attention to visuospatial and executive domains. Fluctuation history from carers. Clock drawing test typically severely impaired
MRI brainOften relatively preserved medial temporal lobes (contrast with AD where hippocampal atrophy is prominent)
Second-line
DaTSCAN (FP-CIT SPECT)Shows reduced dopamine transporter uptake in basal ganglia — distinguishes DLB from AD. Abnormal DaTSCAN is a supportive biomarker in revised criteria
MIBG myocardial scintigraphyReduced cardiac sympathetic innervation — supportive biomarker
Specialist
PolysomnographyConfirms REM sleep behaviour disorder (REM sleep without atonia)
FDG-PETOccipital hypometabolism (cingulate island sign) — differentiates from AD
Management
NICE NG97 (Dementia), 20181
Pharmacological
- AChEIs (donepezil or rivastigmine) — first-line for cognitive symptoms and hallucinations. Often markedly beneficial in DLB
- Memantine: consider if AChEIs not tolerated or as add-on
- Hallucinations: if non-distressing, reassurance may suffice. If treatment needed: low-dose quetiapine (with extreme caution) or clozapine (specialist)
- AVOID typical antipsychotics (haloperidol, chlorpromazine) — EXTREME SENSITIVITY with risk of fatal neuroleptic malignant syndrome
2
Non-pharmacological
- Person-centred care, consistent routine, good lighting (reduce misperception)
- Fall prevention strategies — OT assessment, walking aids, postural hypotension management
- Carer education about fluctuations and hallucinations
- Advance care planning — discuss while capacity retained
3
Symptom-specific
- Parkinsonism: cautious trial of low-dose levodopa (may help motor symptoms but can worsen hallucinations)
- REM sleep behaviour disorder: clonazepam low-dose or melatonin
- Postural hypotension: fludrocortisone, midodrine, compression stockings, fluid/salt intake
- Depression: SSRI (avoid tricyclics — anticholinergic)
Complications
- Antipsychotic sensitivity: Life-threatening reactions to typical antipsychotics — severe parkinsonism, rigidity, NMS, death. Use with EXTREME CAUTION
- Falls: Combination of parkinsonism, postural hypotension, fluctuating attention — high injury risk
- Aspiration pneumonia: Dysphagia from parkinsonism
- Rapid cognitive decline: DLB can progress faster than AD
- Carer burden: Fluctuating cognition and hallucinations are particularly distressing for carers
UKMLA Exam Tips
- 1Triad: fluctuating cognition + visual hallucinations + parkinsonism = Lewy body dementia
- 2ANTIPSYCHOTIC SENSITIVITY is the critical exam point — typical antipsychotics are CONTRAINDICATED in DLB
- 3REM sleep behaviour disorder is a strong predictor — may precede cognitive symptoms by decades
- 4DaTSCAN abnormal in DLB but normal in AD — key differentiating investigation
- 5Relatively preserved medial temporal lobes on MRI (contrasts with AD where hippocampal atrophy is prominent)
- 6AChEIs are often dramatically effective in DLB — more so than in AD
- 71-year rule: dementia before/within 1 year of parkinsonism = DLB; parkinsonism >1 year before dementia = PDD
practicetest your knowledge on lewy body dementiaApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — neurology and beyond.
open q-bank