Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Recognise the cognitive, visual, sleep, motor and autonomic signature of dementia with Lewy bodies, use indicative investigations when uncertainty matters, and treat symptoms while avoiding severe antipsychotic sensitivity and compounding orthostatic or cognitive harm.
DLB is a synucleinopathy with cognitive decline and a characteristic combination of network fluctuation, visual processing dysfunction, hallucinations, sleep disorder and parkinsonism. Visual hallucinations are often detailed people or animals and may initially be recognised as unreal. Misidentification, passage hallucinations and visuospatial errors can coexist. Fluctuations may resemble staring, daytime somnolence or episodes of disorganised speech, but any new acute deterioration still requires a delirium search.
REM sleep behaviour disorder reflects loss of normal muscle atonia during dreaming and may precede dementia by years. Parkinsonism may be relatively symmetric, with rigidity, bradykinesia and gait disturbance; tremor is not essential. Autonomic involvement causes orthostatic hypotension, constipation, urinary dysfunction, sexual dysfunction and temperature or sweating problems. Antipsychotic sensitivity ranges from marked motor worsening and sedation to life-threatening rigidity and autonomic collapse.
Diagnosis is clinical, supported where needed by dopaminergic SPECT, polysomnographic confirmation of REM sleep without atonia or other specialist biomarkers. Mixed Alzheimer pathology is common and can make memory loss more prominent. Cognitive, sleep and orthostatic treatments, and any antipsychotic use, require individual specialist assessment and local shared-care governance.
DLB is a synucleinopathy associated with cognitive decline, fluctuating attention, visual hallucinations, REM sleep behaviour disorder, parkinsonism and autonomic involvement.
Alzheimer pathology commonly coexists with DLB and can make memory loss more prominent, altering the clinical profile and diagnostic certainty.
Misfolded alpha-synuclein accumulates within neurons and synapses, disrupting signalling across arousal, visual, motor, sleep and autonomic systems.
Disrupted visual-association and nigrostriatal systems produce visuospatial errors, recurrent formed hallucinations, bradykinesia, rigidity and gait impairment during disease progression.
Variable network efficiency produces marked changes in alertness and cognition, recurrent visual hallucinations and REM sleep without normal muscle atonia.
Unexpected shifts between coherent alert engagement and pronounced drowsiness, staring or disorganised thought over short periods are characteristic after delirium and medicines are excluded.
Recurrent detailed images of people, children or animals, often with retained partial insight early, carry more diagnostic weight than vague shadows or isolated bereavement experiences.
Dream enactment with vocalisation and complex limb movement during sleep, especially with injury risk, supports synucleinopathy and may long predate daytime cognitive symptoms.
Bradykinesia, rigidity and gait dysfunction not explained by dopamine-blocking drugs provide a core feature even when classic pill-rolling tremor is absent.
Disproportionate sedation, confusion, immobility, rigidity, swallowing decline or autonomic instability after an antipsychotic is a major warning and may require emergency treatment.
Early storage-memory failure without hallucinations, marked fluctuation, REM sleep behaviour disorder or parkinsonism favours typical Alzheimer disease, though mixed pathology is common.
Dementia beginning after well-established Parkinson disease is labelled Parkinson disease dementia; cognitive decline before or near motor onset supports DLB.
Acute hours-to-days fluctuation from infection, pain or medicines indicates delirium, which can coexist with and be amplified by underlying DLB.
Early severe autonomic failure, stridor, gaze palsy or recurrent falls may favour multiple-system atrophy or progressive supranuclear palsy over DLB.
Parkinsonism, visual misperception and autonomic hypotension combine to cause recurrent falls, collapse, fractures and loss of mobility.
Dopamine blockade can provoke profound rigidity, sedation, autonomic collapse or neuroleptic malignant syndrome, making behavioural prescribing unusually hazardous.
Progressive swallowing, bladder, bowel and blood-pressure dysfunction causes aspiration, infection, constipation, malnutrition and substantial care dependence.
Hallucinations, sleep disturbance and cognitive fluctuation can be frightening and unpredictable, increasing safeguarding concerns and sustained strain on families.
Attention and visuoperceptual deficits can dominate before severe episodic-memory storage failure, so a memory-weighted screen can understate early DLB disability.
Well-formed visions may be neutral or even pleasant; treatment burden is not justified merely because a symptom is unusual when the person is safe and untroubled.
Dream enactment often predates cognitive and motor diagnosis by years, making an informed bed-partner history diagnostically valuable.
DLB and Parkinson disease dementia share biology; timing of dementia relative to motor onset provides consistent clinical terminology rather than a sharp mechanistic boundary.
Unexpected profound decline after a small antipsychotic dose should prompt immediate treatment and reconsideration of an unrecognised Lewy body syndrome.
Calling marked short-timescale fluctuation ordinary forgetfulness misses a core diagnostic feature, while failing to exclude delirium creates equal harm.
Prescribing haloperidol reflexively for non-distressing visual hallucinations can cause severe rigidity, dysphagia, confusion and autonomic collapse.
Ruling out DLB from absent tremor ignores that bradykinesia and rigidity are sufficient parkinsonian manifestations.
Treating orthostatic falls only with physiotherapy without reviewing blood pressure and medicines leaves a major autonomic cause unaddressed.
Escalating levodopa until motor signs disappear may worsen hallucinations and confusion for limited functional gain.
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A 74-year-old with progressive cognitive decline has recurrent detailed visual hallucinations, dream enactment and spontaneous bradykinesia with rigidity. Which diagnosis best integrates these features?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
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Monitor nausea, diarrhoea, weight loss, bradycardia, syncope, falls and tremor. Check patch technique and remove the old patch before a new one; restart low after a significant interruption.
Monitor hallucinations, confusion, orthostatic hypotension, nausea and dyskinesia. Avoid chasing a normal motor examination with high doses, and never stop established dopaminergic therapy abruptly.
Haloperidol and potent dopamine blockade can cause catastrophic worsening. Explain stroke and mortality risk, monitor rigidity, consciousness, swallowing and autonomic state after every change, and stop if benefit is absent.