Synopsis
Recognise characteristic but overlapping dementia profiles, separate chronic subtype features from delirium and acute stroke, select specialist tests only when they change management, and avoid subtype-specific medication harms and ineffective treatment.
- Alzheimer's disease often begins with progressive difficulty learning and recalling recent information, but language, visuospatial or executive variants occur and mixed pathology is common.
- Vascular dementia may follow a stroke or evolve gradually through small-vessel disease; early slowing, executive difficulty, gait change and focal signs can outweigh memory loss.
- Dementia with Lewy bodies commonly combines fluctuating cognition, recurrent well-formed visual hallucinations, REM-sleep behaviour and spontaneous parkinsonism, with falls and autonomic symptoms as supportive clues.
- Frontotemporal dementia often presents earlier with disinhibition, apathy, loss of empathy, compulsive behaviour, altered eating or progressive language impairment while episodic memory is relatively preserved initially.
- Use validated clinical subtype criteria and expect overlap; vascular imaging burden or one characteristic symptom cannot establish a diagnosis alone.
- NICE recommends structural imaging for reversible structural causes and subtype support unless dementia is already well established and the subtype is clear.
- When DLB is suspected and diagnosis is uncertain, use iodine-123 FP-CIT SPECT; a normal result does not independently exclude DLB.
- When vascular dementia is suspected but subtype remains uncertain, use MRI if possible or CT if MRI is unavailable or contraindicated; do not diagnose from lesion burden alone.
- AChE inhibitors and memantine have subtype-specific indications: do not offer either for frontotemporal dementia and use them in vascular dementia only when relevant comorbid dementia is suspected.
- Antipsychotics can worsen motor symptoms and cause severe sensitivity in Lewy-body and Parkinson's disease dementia; analyse distress causes and seek specialist advice before use.
Key red flags
An abrupt focal neurological syndrome is a possible stroke even in established vascular dementia and requires emergency assessment from the last-known-well time.
New fluctuating inattention or altered arousal over hours or days suggests delirium superimposed on dementia, not an ordinary subtype fluctuation.
Repeated syncope, severe autonomic hypotension, falls, REM-sleep behaviours and visual hallucinations with parkinsonism support Lewy-body assessment and increase medicine risk.
Marked rigidity, sedation, dysphagia, fever or autonomic instability after antipsychotic exposure in possible Lewy-body dementia needs urgent cessation and medical review.
Rapid progression over weeks or a few months, seizures, myoclonus, ataxia or unusual neurological signs requires an urgent rapidly progressive dementia pathway.
Early major behavioural or language change, especially before age sixty-five, should prompt frontotemporal and young-onset specialist assessment rather than a moral or psychiatric label.
Investigation priorities
Identify the first affected cognitive domain, progression pattern, neurological symptoms, behaviour and daily consequences.
Management branches
Specialist assessment confirms dementia but the disease subtype or combination remains uncertain.
- Map first symptoms, course, function, hallucinations, sleep, parkinsonism, focal signs, behaviour and language with person and collateral accounts.
- Apply validated subtype criteria and structural imaging, treating delirium, depression, sensory and medicine contributors in parallel.
- Use additional biomarker or functional imaging only when uncertainty remains and the result would change medicines, counselling or planning.