Lewy Body and Frontotemporal Dementia
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Direct answer
Dementia with Lewy bodies is a neurodegenerative dementia defined by fluctuating cognition, recurrent well-formed visual hallucinations, REM sleep behaviour disorder and parkinsonism. Frontotemporal dementia is a group of disorders with early behavioural change or language decline and frontal or anterior temporal atrophy on imaging. The two are separated mainly by fluctuation and hallucinations in Lewy body disease, against personality change and early language loss in frontotemporal disease.
What you must remember
- Core DLB features: fluctuating cognition, recurrent well-formed visual hallucinations, REM sleep behaviour disorder and spontaneous parkinsonism; two core features make the diagnosis probable.
- Supportive DLB features: severe neuroleptic sensitivity, postural instability, syncope or transient unresponsiveness, hyposmia and autonomic dysfunction.
- DaT SPECT: reduced striatal dopamine transporter uptake supports DLB, whereas uptake is normal in Alzheimer disease.
- DLB treatment: cholinesterase inhibitors such as rivastigmine or donepezil help cognition and hallucinations, and typical antipsychotics are avoided.
- Behavioural variant FTD: early disinhibition, apathy, loss of empathy, hyperorality and compulsive behaviour, with frontal or insular atrophy.
- Semantic variant FTD: fluent speech with impaired naming and single-word comprehension, with anterior temporal atrophy.
- Non-fluent variant FTD: effortful, agrammatic speech with apraxia of speech, with left perisylvian or frontal atrophy.
- Genetics: C9orf72, MAPT and GRN mutations are the commonest genetic causes of familial FTD, and C9orf72 expansions are also linked with motor neuron disease.
Weighing features in a fluctuating dementia
A 70-year-old man has three years of fluctuating confusion, recurrent visitors in his room and a history of acting out dreams. The steps below show how the features are weighed before a diagnosis is made.
- Count core features: two core features, such as fluctuation and visual hallucinations, make DLB probable even before a biomarker is available.
- Check supportive features: neuroleptic sensitivity, hyposmia, syncope and autonomic failure strengthen the case.
- Use DaT imaging: reduced striatal dopamine transporter uptake supports DLB and helps exclude it when the scan is normal.
- Separate from Alzheimer disease: early amnesia favours Alzheimer disease, whereas early hallucinations, fluctuation and parkinsonism favour Lewy body disease.
- Look for frontotemporal features: early personality change, disinhibition or language loss direct attention to FTD and its frontal or temporal atrophy.
- Name the variant: the dominant early feature decides between behavioural, semantic and non-fluent subtypes.
- Plan management: cholinesterase inhibitors for DLB, avoidance of typical antipsychotics, and non-drug measures for the behavioural symptoms of FTD.
Where the stem misleads on dementia type
Most errors come from relying on memory loss, which is often less prominent early in Lewy body disease.
- Trap: giving haloperidol for hallucinations in a patient with DLB Correct: severe neuroleptic sensitivity makes typical antipsychotics dangerous, so cholinesterase inhibitors are preferred.
- Trap: using memory loss to diagnose DLB Correct: early fluctuations and hallucinations point to Lewy body disease, while early amnesia points to Alzheimer disease.
- Trap: attributing personality change in a middle-aged patient to depression alone Correct: early disinhibition, apathy and loss of empathy with preserved memory suggest behavioural variant FTD.
- Trap: assuming all primary progressive aphasia is the same Correct: semantic and non-fluent variants differ in speech pattern and in the lobe affected, anterior temporal and frontal respectively.
Frequently asked questions
Which features make dementia with Lewy bodies probable?
Two core features, from fluctuating cognition, recurrent well-formed visual hallucinations, REM sleep behaviour disorder and parkinsonism, make dementia with Lewy bodies probable. Supportive features such as severe neuroleptic sensitivity and hyposmia strengthen the diagnosis.
Why are antipsychotics avoided in dementia with Lewy bodies?
Patients with dementia with Lewy bodies have severe sensitivity to typical antipsychotics, which can cause profound parkinsonism and neuroleptic malignant syndrome. Cholinesterase inhibitors are used instead for hallucinations and cognitive symptoms.
What does a DaT scan show in Lewy body disease?
A DaT SPECT scan shows reduced dopamine transporter uptake in the striatum in dementia with Lewy bodies, reflecting nigrostriatal degeneration. Uptake is normal in Alzheimer disease, so the scan helps separate the two conditions.
Which genes are commonest in familial frontotemporal dementia?
C9orf72, MAPT and GRN mutations are the commonest genetic causes of familial frontotemporal dementia. C9orf72 expansions are also linked with motor neuron disease, which is why the two conditions can overlap clinically.
How does semantic variant frontotemporal dementia present?
Semantic variant frontotemporal dementia presents with fluent speech, impaired naming and poor single-word comprehension, with anterior temporal atrophy on imaging. Episodic memory and visuospatial function are relatively preserved early, which helps distinguish it from Alzheimer disease.