ICD-116D82	DEMENTIA DUE TO LEWY BODY DISEASE (DLB) Dementia due to Lewy body disease
ICD-10F02.8	Dementia in other specified diseases classified elsewhere
DSM-5-TRG31.83 + F02.8x	Major or Mild Neurocognitive Disorder With Lewy Bodies

1. Definition and nosology

Lewy Body Dementia (DLB; ICD-11: 6D82; DSM-5-TR: G31.83 + F02.8x) — dementia developing from α-synuclein pathology; classic triad — cognitive fluctuations, visual hallucinations, parkinsonism. 5–15% of dementias.

Parkinson's disease dementia (PDD) — same pathology, but dementia develops at least 1 year after parkinsonism; DLB and PDD clinical spectrum.

2. History

• Lewy F. (1912) — Description of Lewy bodies in Parkinson's disease.
• McKeith I. (1996, 2017 update) — DLB consensus criteria.

3. Epidemiology

• 5–15% of dementia cases; relatively higher in males.
• Prevalence increases with age ≥65.
• Comorbidity: depression, delusions, REM sleep behavior disorder.

4. Aetiology and pathogenesis

• α-Synuclein aggregation — Lewy bodies in cortical and substantia nigra regions.
• SNCA, LRRK2, and GBA genes confer risk.

5. Clinical features

Four core clinical features (McKeith 2017)

• Fluctuating cognition — pronounced variation in attention and alertness (hours-days).
• Recurrent visual hallucinations — typically well formed and detailed (human, animal figures); the patient may be relatively tolerant of them.
• REM sleep behaviour disorder (RBD) — may precede cognitive decline by years.
• Parkinsonism — one or more spontaneous cardinal features: bradykinesia, rest tremor or rigidity (tremor typically milder than in Parkinson's disease).

Indicative biomarkers

• Reduced dopamine transporter uptake in the basal ganglia on SPECT/PET (123I-FP-CIT).
• Abnormal (low uptake) 123I-MIBG myocardial scintigraphy.
• Polysomnographic confirmation of REM sleep without atonia.

Supportive clinical features

• Severe antipsychotic sensitivity — neuroleptic malignant syndrome-like reaction (not part of the diagnostic algorithm).
• Postural instability, repeated falls, syncope, severe autonomic dysfunction, hypersomnia, hyposmia, systematised delusions, apathy, anxiety, depression.

6. Diagnosis

6.1 Unified diagnostic criteria (McKeith 2017)

Probable DLB: 2+ core clinical features (with or without indicative biomarkers), or 1 core feature + 1 or more indicative biomarkers. It must not be diagnosed on biomarkers alone.

Possible DLB: only 1 core clinical feature with no indicative biomarker; or 1 or more indicative biomarkers with no core clinical feature.

6.2 Source-specific clarifications

• McKeith I. et al. Neurology 2017 — diagnostic consensus.
• DAT-SPECT or 123I-MIBG cardiac scintigraphy — indicative biomarkers (not supportive).

6.3 Diagnostic algorithm

1. Clinical interview + informant (especially RBD).
2. MoCA, MMSE, neuropsychological (visuospatial and executive function dominant).
3. Neurological examination.
4. Brain MRI (hippocampal atrophy less than in Alzheimer's).
5. DAT-SPECT (when indicated).
6. Polysomnography — RBD confirmation.

6.4 Differential diagnosis

7. Examination and assessment

• MoCA, neuropsychological testing.
• Polysomnography (RBD).
• DAT-SPECT.
• Brain MRI.

8. Treatment

1. AChEI (rivastigmine, donepezil) — In DLB particularly effective (cortical acetylcholine reduction stronger than in Alzheimer); rivastigmine McKeith I. Lancet 2000 RCT.
2. Memantine — for moderate-severe cases.
3. Parkinsonism — use levodopa with caution; it can intensify psychotic symptoms.
4. For visual hallucinations: non-pharmacological measures first. In refractory cases quetiapine or clozapine at low dose; Typical antipsychotics (haloperidol) and risperidone are contraindicated — severe neuroleptic sensitivity reaction.
5. RBD — melatonin (3–12 mg at night) or clonazepam (low dose).
6. For BPSD, non-pharmacological measures come first.
7. FDA antipsychotic black box in elderly dementia patients.

Source-specific specifications

• McKeith I. Lancet 2000 — rivastigmine in DLB.
• NICE NG97 — rivastigmine or donepezil for DLB.
• Antipsychotic sensitivity — McKeith I. reviews.

Treatment methods

1. Rivastigmine AChEI — In DLB, specifically effective; patch and oral.
2. Quetiapine/Clozapine (refractory psychosis) — Low dose; clozapine is the safest but requires monitoring.
3. Melatonin for RBD — 3–12 mg at night.
4. DAT-SPECT — Indicative diagnostic biomarker.

9. Prognosis

• Mean life expectancy from diagnosis 5–8 years; sometimes shorter than Alzheimer's.
• Antipsychotic reaction is a critical complication.

10. Myths and misconceptions

Myth 1: “DLB is only a subtype of Alzheimer's”

Evidence: distinct pathological and clinical unit; α-synuclein vs amyloid-β/tau; antipsychotic sensitivity is critical difference.

Myth 2: “Haloperidol is safe in DLB”

Evidence: Haloperidol and risperidone are contraindicated — neuroleptic malignant syndrome-like reaction, mortality risk high.

Myth 3: “Visual hallucinations always require treatment”

Evidence: Some patients are tolerant to hallucinations; different approach if no distress.

Myth 4: “Levodopa fully cures parkinsonism in DLB”

Evidence: The levodopa response is smaller than in Parkinson's disease; it can exacerbate psychotic symptoms; balance is required.

Myth 5: “RBD is an insignificant symptom”

Evidence: RBD is a prodrome of α-synucleinopathy (DLB, Parkinson's, MSA) — future development in 80%+ within 10-15 years.

11. Sources

1. WHO. ICD-11. 6D82 Dementia due to Lewy body disease. 2024.
2. APA. DSM-5-TR. 2022.
3. McKeith I.G. et al. Diagnosis and management of dementia with Lewy bodies: Fourth consensus report. Neurology 2017;89(1):88–100.
4. McKeith I. et al. Efficacy of rivastigmine in dementia with Lewy bodies: a randomised, double-blind, placebo-controlled international study. Lancet 2000;356(9247):2031–2036.
5. NICE NG97. 2018.