Lewy Body Dementia

Dementia with Lewy bodies (DLB) is an alpha synucleinopathy causing progressive dementia with fluctuating cognition, visual hallucinations, REM sleep behaviour disorder and parkinsonism.

• Second commonest neurodegenerative dementia (15 to 20% of cases); onset after 50; survival 5 to 8 years.

• Parkinson disease dementia is diagnosed when dementia begins more than 1 year after parkinsonism (1 year rule).

• Severe neuroleptic sensitivity in up to 50%.

• Core: fluctuating attention and alertness, recurrent well formed visual hallucinations, REM sleep behaviour disorder (may precede by years), parkinsonism (bradykinesia, rigidity, rest tremor).

• Supportive: severe neuroleptic sensitivity, postural instability, falls, syncope, autonomic dysfunction, hypersomnia, hyposmia, depression, delusions.

• Visuospatial and executive dysfunction more than amnesia early.

• McKeith criteria (2017): dementia plus two core features (probable DLB) or one core plus one indicative biomarker.

• Indicative biomarkers: reduced dopamine transporter uptake (DaTscan), abnormal MIBG myocardial scintigraphy, polysomnographic REM sleep without atonia.

• Supportive: relative preservation of medial temporal lobes on MRI, posterior occipital hypometabolism on FDG PET ("cingulate island sign"), slow wave EEG.

• Exclude delirium, Alzheimer disease, vascular dementia, medication effects. Skin biopsy and seed amplification assay for alpha synuclein emerging.

• Avoid antipsychotics (haloperidol, risperidone) which risk severe sensitivity reactions and death; if essential, use low dose quetiapine 12.5 to 50 mg or clozapine 6.25 to 25 mg, or pimavanserin 34 mg.

• Cholinesterase inhibitors: rivastigmine 1.5 mg twice daily increasing to 6 mg twice daily (or patch 4.6 to 13.3 mg/day), donepezil 5 to 10 mg daily; improves cognition, hallucinations and fluctuations. Memantine 10 mg twice daily as alternative.

• Parkinsonism: levodopa at the lowest dose (can worsen hallucinations); avoid anticholinergics and dopamine agonists.

• REM sleep behaviour disorder: clonazepam 0.25 to 1 mg or melatonin 3 to 12 mg at night, bedroom safety.

• Orthostatic hypotension: fludrocortisone, midodrine, compression stockings. Depression: SSRIs. Constipation: macrogol.

• Review delirium triggers, avoid anticholinergic drugs; carer support, driving assessment, advance planning.