Lewy body dementia is the second most common neurodegenerative dementia after Alzheimer’s disease, and one of those most often mistaken for it. Diagnosed on average around age 76, it rarely begins with forgetfulness: alertness that varies from one hour to the next, visual hallucinations, agitated dreams, falls. These signs set it apart from Alzheimer’s. Recognizing them early protects the patient, because some common drugs, antipsychotics (also called neuroleptics), can trigger serious reactions in people with this disease.
In brief – Lewy body dementia is a neurodegenerative disease that combines cognitive decline with clumps of alpha-synuclein, the Lewy bodies, inside neurons of the cortex and brainstem. It differs from Alzheimer’s disease through four core features: strongly fluctuating attention, detailed and recurrent visual hallucinations, REM sleep behavior disorder (the sleeper acts out their dreams) and parkinsonian signs. Memory often stays fairly well preserved at first, while spatial orientation fails early. The 2017 international criteria support a probable diagnosis when two core features are present, or one combined with an abnormal test: DaTscan, cardiac scintigraphy or a sleep recording. A major practical point: in a British series, 13 of 16 patients exposed to antipsychotics reacted badly, 7 of them severely. Cholinesterase inhibitors improve attention and hallucinations, without stopping the disease.
What is Lewy body dementia?
Lewy body dementia, which doctors call dementia with Lewy bodies (DLB), combines cognitive decline severe enough to interfere with daily life with abnormal protein deposits inside neurons. These deposits, the Lewy bodies, are named after the German neurologist Friedrich Lewy, who described them in the early 20th century in patients with Parkinson’s disease. A Cambridge team showed that they are largely made of a single protein, alpha-synuclein (Spillantini et al., 1997).
This dementia remains underdiagnosed. A systematic review from Newcastle University estimates that it accounts for 4.2% of dementias diagnosed in the general population and 7.5% in specialist clinics, or about one dementia in 13 seen by a specialist (Vann Jones and O’Brien, 2014). Across nine British services, its share ranged from 2.4% to 5.9% depending on the service, a gap the authors attribute mainly to diagnostic practices (Kane et al., 2018).
The World Health Organization lists dementia with Lewy bodies among the common forms of dementia, alongside vascular dementia. Alzheimer’s disease remains by far the most frequent, with 60 to 70% of the 57 million cases recorded worldwide in 2021.
Neurologists speak of “Lewy body diseases” to describe a family that also includes Parkinson’s disease. The boundary is a matter of timing. If dementia appears before the movement problems, or within the year that follows, it is dementia with Lewy bodies. If it develops in someone who has had Parkinson’s for more than a year, it is Parkinson’s disease dementia. This “one-year rule” appears in the fourth international consensus of the DLB Consortium (McKeith et al., 2017).
What Lewy bodies do to the brain
Lewy bodies disrupt several nerve circuits at once, which explains a more varied picture than in Alzheimer’s disease. Alpha-synuclein, a normal protein of nerve endings, misfolds, aggregates and forms clumps that hamper the work of neurons, then their survival. This failure of protein recycling links the disease to the loss of proteostasis, one of the biological hallmarks of aging. According to the National Institute of Neurological Disorders and Stroke, the disease also reaches the olfactory pathways and the nerves of the intestine.
- The cholinergic system is hit early and hard. The loss of acetylcholine neurons contributes to attention problems, fluctuations and hallucinations, and justifies the use of cholinesterase inhibitors.
- The dopamine pathway of the substantia nigra, the same region as in Parkinson’s disease, deteriorates. The result is slowness, stiffness and sometimes tremor, as well as an abnormal DaTscan.
- The areas of the cortex that process vision and space are affected early. Hence the errors of perception, the difficulty copying a figure and the hallucinations.
- The autonomic nervous system is involved too: nerves of the heart, the gut and the blood vessels. This shows up as a drop in blood pressure on standing, constipation and urinary problems.
- In the brainstem, damage to the nuclei that paralyze the muscles during REM sleep lets the sleeper act out their dreams.
The two diseases often overlap. According to the Lewy Body Dementia Association, up to one person with Alzheimer’s in two may show alpha-synuclein changes compatible with Lewy body disease. The 2017 consensus also adapted its neuropathological criteria to account for coexisting Alzheimer’s lesions. These mixed forms blur the signs and explain some of the diagnostic errors.
| Criterion | Dementia with Lewy bodies | Alzheimer’s disease |
|---|---|---|
| Main protein | Aggregated alpha-synuclein (Lewy bodies) | Beta-amyloid (plaques) and tau protein |
| First regions affected | Brainstem, visual and association cortex, acetylcholine neurons | Hippocampus and medial temporal cortex, the seat of memory |
| Hippocampus on MRI | Relatively preserved at first | Early atrophy |
| Dopamine neurons | Affected, abnormal DaTscan | Preserved, normal DaTscan |
| Heart nerves | Often affected, abnormal MIBG scintigraphy | Usually normal |
| Biomarker under study | Alpha-synuclein “seeding” activity | Low Aβ42, high tau in cerebrospinal fluid |
The 7 signs that set Lewy body dementia apart from Alzheimer’s, according to science
In typical Alzheimer’s disease, memory for recent events fails first. With Lewy bodies, decline more often begins with attention, spatial vision and non-cognitive signs. The fourth international consensus lists four core clinical features and several supportive features that guide the doctor (McKeith et al., 2017).
1. Alertness that fluctuates from one hour to the next
The person seems present and sharp in the morning, then absent, drowsy or confused in the afternoon, with no apparent cause. These fluctuations affect wakefulness and attention more than memory. A Mayo Clinic team interviewed the relatives of 70 patients with dementia with Lewy bodies, 70 patients with Alzheimer’s and 200 older adults without dementia. Four features made the difference: daytime drowsiness, at least 2 hours of sleep during the day, staring into space for long periods and episodes of disorganized speech. Three or four of these features were present in 63% of DLB patients, compared with 12% of Alzheimer’s patients and 0.5% of controls (Ferman et al., 2004).
2. Precise and recurrent visual hallucinations
Hallucinations linked to Lewy bodies are typically well formed: a child sitting on the sofa, a cat in the hallway, strangers in the garden. The person describes them in detail and sometimes stays calm in front of them. In a San Diego series of 23 DLB patients and 94 Alzheimer’s patients confirmed at autopsy, visual hallucinations present from the first visit were 99% specific for Lewy bodies. Their positive predictive value reached 83%. Yet they affected only 22% of DLB patients at this early stage (Tiraboschi et al., 2006). Their absence therefore does not rule out the diagnosis.
3. Spatial orientation affected before memory
Parking the car, reading a map, copying two intersecting pentagons or judging the height of a step becomes difficult early on. In the same series of 117 autopsied patients, these visuospatial problems affected 74% of patients with Lewy bodies from the start, and their absence had a negative predictive value of 90%. Conversely, verbal memory and the ability to name objects hold up better than in Alzheimer’s disease at the same stage (Ferman et al., 2002). Another San Diego study followed 35 DLB patients with severe visuospatial impairment at baseline: 40% already had hallucinations, and 61% of the others developed them over an average follow-up of 5 years (Hamilton et al., 2012).
4. Dreams acted out aloud
REM sleep behavior disorder shows up as shouting, punching or kicking during dreams, often dreams of being chased or attacked. Normally the muscles are paralyzed during REM sleep, but here that lock gives way. According to the 2017 consensus, it affects 76% of autopsy-confirmed cases, compared with 4% of other dementias, and often begins several years before the other symptoms. A 24-center study followed 1,280 people with this isolated disorder, aged 66 on average. Each year, 6.3% progressed to Parkinson’s disease, dementia with Lewy bodies or multiple system atrophy, and 73.5% had progressed after 12 years (Postuma et al., 2019). The spouse is often the first witness.
5. Early parkinsonian signs
Slow movements, stiffness, small steps, a less expressive face, sometimes a resting tremor: these signs frequently set in as the disease progresses. In the San Diego autopsy series, they were present at the first visit in only 26% of DLB patients (Tiraboschi et al., 2006). They differ from Parkinson’s disease in their timing, since the dementia comes first or at the same time. Advanced Alzheimer’s disease can also cause slowness and stiffness, which makes the neurological examination valuable.
6. Extreme sensitivity to antipsychotics
This is the sign that matters most in practice. Antipsychotics (neuroleptics) prescribed for agitation or hallucinations, such as haloperidol, can trigger sudden stiffness, confusion, falls or even a life-threatening state. A Newcastle team reviewed the records of 41 patients whose diagnosis had been confirmed at autopsy. Among the 16 patients with dementia with Lewy bodies treated with antipsychotics, 13 reacted adversely, 7 of them severely, and these severe reactions came with increased mortality within the year. Among exposed Alzheimer’s patients, only one in 14 had a severe reaction (McKeith et al., 1992).
7. Falls, fainting spells and dysautonomia
A drop in blood pressure on standing, long-standing constipation, urinary problems, loss of smell, brief losses of consciousness: the autonomic nervous system is affected early. These signs are among the supportive features of the 2017 criteria. In a prospective Newcastle study of 179 people over 65, Lewy body disease multiplied the risk of falling over one year by 3.3. Symptomatic orthostatic hypotension multiplied it by 2.1, while higher physical activity reduced it (Allan et al., 2009).
| Sign | Dementia with Lewy bodies | Typical Alzheimer’s disease | Key data |
|---|---|---|---|
| Fluctuating alertness, typical of Lewy bodies | Marked, from one hour or one day to the next | Rare at first | 3 or 4 features in 63% vs 12% |
| Visual hallucinations | Early, detailed, recurrent | Later and less common | 99% specificity at onset |
| Space and memory | Space affected early, memory better preserved | Memory for recent events affected first | Visuospatial problems in 74% at onset |
| Agitated REM sleep | Common, often years earlier | Uncommon | 76% of autopsied cases vs 4% |
| Parkinsonian signs | Early or at the same time as the dementia | Late, at an advanced stage | 26% at the first visit |
| Reaction to antipsychotics | Common and sometimes severe | Rare | 7 severe reactions out of 16 vs 1 out of 14 |
| Falls and low blood pressure | Early | Later | Risk of falling multiplied by 3.3 |
Which tests confirm Lewy body dementia?
Diagnosis remains primarily clinical, but under the 2017 criteria three so-called indicative tests strengthen the suspicion. Dementia with Lewy bodies is considered probable when two core features are present, or when a single core feature is combined with at least one abnormal indicative test. Brain MRI is mainly used to rule out other causes, such as a tumor or vascular lesions.
The DaTscan, a brain scan that measures the dopamine transporter, is the best-studied test. In a European phase III study of 326 patients, an abnormal scan detected probable dementia with Lewy bodies with a sensitivity of 77.7% and a specificity of 90.4%, particularly against Alzheimer’s disease (McKeith et al., 2007).
Cardiac MIBG scintigraphy examines the sympathetic nerves of the heart, which Lewy bodies destroy early. A Japanese multicenter study of 133 patients found a sensitivity of 68.9% and a specificity of 89.1%, then 77.4% and 93.8% at the mild dementia stage (Yoshita et al., 2015). Several authors reported ties to the tracer’s manufacturers. Coronary artery disease, heart failure, diabetes, neuropathy or certain drugs can also skew the result, the 2017 consensus points out. Finally, polysomnography, a sleep recording made in a laboratory, confirms REM sleep without muscle relaxation.
Two recent tests look directly for alpha-synuclein. In 439 cerebrospinal fluid samples, an amplification test called RT-QuIC detected the protein’s “seeding” activity with a sensitivity of 95.3% in Lewy body diseases. Its specificity reached 98% in 101 brains without Lewy bodies (Rossi et al., 2020). A skin biopsy, analyzed at 30 US centers, found phosphorylated alpha-synuclein in 96% of patients with dementia with Lewy bodies and 3.3% of controls (Gibbons et al., 2024). Several authors of this study held interests in the company that markets the test, and these results still need to be validated in unselected populations.
| Test | What it measures | Reported accuracy | Status |
|---|---|---|---|
| DaTscan | Dopamine transporter in the basal ganglia | Sensitivity 77.7%, specificity 90.4% (326 patients) | Indicative test |
| Cardiac MIBG scintigraphy | Sympathetic nerves of the heart | Sensitivity 68.9%, specificity 89.1% (133 patients) | Indicative test |
| Polysomnography | Muscle tone during REM sleep | Confirms REM sleep behavior disorder | Indicative test |
| Brain MRI | Hippocampal volume, other causes | Hippocampus relatively preserved | Supportive evidence |
| Cerebrospinal fluid RT-QuIC | Alpha-synuclein “seeding” activity | Sensitivity 95.3%, specificity 98% | Being validated |
| Skin biopsy | Phosphorylated alpha-synuclein in skin nerves | Positive in 96% of DLB cases, 3.3% of controls | Being validated |
Suspected Lewy body dementia: what the diagnosis changes in practice
Telling dementia with Lewy bodies apart from Alzheimer’s disease changes three things: the drugs to avoid, those that help, and fall prevention. Yet a long diagnostic journey is common. In a survey of 962 American caregivers, the first diagnosis given was Parkinson’s disease in 39% of cases, Alzheimer’s disease in 36% and a psychiatric disorder in 24%. Half of the patients had seen more than 3 doctors, over more than 10 appointments in a year, before getting the right diagnosis (Galvin et al., 2010).
The pathway goes through the family doctor, then a memory clinic or a neurologist. The UK’s National Institute for Health and Care Excellence (NICE) describes this process in its dementia guideline, which recommends using the international consensus criteria to diagnose dementia with Lewy bodies. To place the two diseases side by side, our article on preventing Alzheimer’s disease details the modifiable risk factors, and the one on Parkinson’s disease risk factors looks at the same protein from the movement angle.
On the treatment side, cholinesterase inhibitors are the best studied. In an international trial of 120 patients, rivastigmine, up to 12 mg a day for 20 weeks, reduced apathy, anxiety, delusions and hallucinations. Overall, 63% of treated patients improved by at least 30%, compared with 30% on placebo, and the benefits faded once treatment stopped (McKeith et al., 2000). In Japan, donepezil at 5 mg a day raised the MMSE score by 3.8 points compared with placebo over 12 weeks in 140 patients (Mori et al., 2012).
A meta-analysis of 44 studies confirms the value of these two drugs for cognition and psychiatric symptoms. Memantine appears well tolerated but of little use, and olanzapine, quetiapine and risperidone show no efficacy (Stinton et al., 2015). The prognosis also differs: a meta-analysis of 11 studies and 22,952 patients puts the average survival after diagnosis at 4.1 years in dementia with Lewy bodies versus 5.7 years in Alzheimer’s disease, with a 35% higher risk of death (Mueller et al., 2019). In a Cambridge cohort, crude median survival was 3.7 years in 251 DLB patients, compared with 7.0 years in 222 Alzheimer’s patients (Price et al., 2017).
| Drug or measure | Type of study | Main result | What to remember |
|---|---|---|---|
| Rivastigmine | Trial of 120 patients over 20 weeks | 63% improved by at least 30%, vs 30% on placebo | Nausea and vomiting more frequent |
| Donepezil | Japanese trial of 140 patients over 12 weeks | MMSE improved by 3.8 points at 5 mg a day | Well tolerated in the trial |
| Memantine | Meta-analysis of 44 studies | Well tolerated, limited benefits | Discussed case by case |
| Typical antipsychotics | Autopsy series of 41 patients | 7 severe reactions in 16 exposed DLB patients | To be avoided |
| Olanzapine, quetiapine, risperidone | Meta-analysis of 44 studies | No proven efficacy | Great caution |
| Physical activity | Prospective study of 179 people | Fewer falls when activity is higher | Adapted and supervised |
Advice for families facing Lewy body dementia
Families spot the signs of the disease well before the doctor, who sees the patient for only a few minutes, sometimes on a good day. A log kept for three weeks makes the consultation far more useful. These simple steps also make daily life safer.
- Write down every day the moments of absence, the drowsiness, the length of naps and the disjointed sentences. These are the four fluctuation features validated by the Mayo Clinic team.
- Describe the hallucinations without disputing them: what the person sees, at what time, in what lighting. Good lighting in the evening reduces the shadowy areas that encourage misperceptions.
- Report agitated dreams to the doctor and make the bedroom safe. Move the nightstand and hard objects away from the bed, and consider separate beds if the partner is being hit.
- Measure blood pressure lying down, then standing after 3 minutes, if there is dizziness on getting up. A drop of at least 20 mmHg in systolic pressure, or 10 mmHg in diastolic pressure, defines orthostatic hypotension.
- Have “antipsychotic (neuroleptic) sensitivity” written in the medical record, and keep this note in the wallet for emergencies.
- Keep up suitable physical activity, with walking, balance work or physical therapy. In the Newcastle study, each additional point of activity reduced the risk of falling by about 17%.
- Look after the caregiver too: in France, support and respite services and family associations exist throughout the country; ask the care team about their equivalents where you live.
No measure has been shown to prevent Lewy body dementia. The Lancet Commission identified 14 modifiable risk factors for dementia of all causes, which may account for about 45% of cases (Livingston et al., 2024). They remain a reasonable basis for protecting the brain, with no guarantee specific to Lewy bodies. The current room for action lies mainly in early recognition, especially of the agitated dreams described in our article on frequent nightmares, which point toward neuroprotection trials.
Frequently asked questions about Lewy body dementia
What is the difference between Lewy body dementia and Alzheimer’s disease?
Alzheimer’s disease most often begins with forgetting recent events, linked to amyloid plaques and tau protein in the hippocampus. Dementia with Lewy bodies, caused by clumps of alpha-synuclein, tends to begin with problems of attention and spatial vision. Fluctuating alertness, visual hallucinations, agitated dreams and parkinsonian signs come on top of these. The two types of lesions often coexist.
How do you recognize the fluctuations of Lewy body dementia?
Families describe a person who is lucid at some moments, then absent or confused a few hours later. Four features are the most telling: daytime drowsiness, daytime sleep of 2 hours or more, staring into space and episodes of disorganized speech. In a Mayo Clinic study, three or four of these features were found in 63% of affected patients, compared with 12% of Alzheimer’s patients.
Why are antipsychotics dangerous for people with Lewy bodies?
Lewy bodies destroy some of the dopamine neurons. Antipsychotics (neuroleptics), which block dopamine receptors, can then sharply worsen stiffness, confusion and falls. In a British series confirmed at autopsy, 7 of 16 exposed patients had a severe reaction, compared with 1 of 14 with Alzheimer’s disease. Any treatment for hallucinations should be discussed with the neurologist.
Which tests confirm Lewy body dementia?
Diagnosis rests first on the clinical examination and the account given by family members. Under the 2017 international criteria, three tests strengthen the suspicion: the DaTscan, which shows the loss of dopamine neurons, cardiac MIBG scintigraphy and a sleep recording. MRI is mainly used to rule out other causes. Alpha-synuclein tests on cerebrospinal fluid or skin are being validated.
Do agitated dreams signal Lewy body disease?
Not always, but a confirmed REM sleep behavior disorder is a serious signal. In a 24-center study of 1,280 people, 6.3% progressed each year to Parkinson’s disease, dementia with Lewy bodies or multiple system atrophy, and 73.5% after 12 years. Ordinary nightmares, without shouting or violent movements, do not carry this meaning.
What is life expectancy with Lewy body dementia?
A meta-analysis of 11 studies and nearly 23,000 patients puts the average survival after diagnosis at 4.1 years, compared with 5.7 years for Alzheimer’s disease. The risk of death is 35% higher. The reasons for this gap remain poorly understood. In a Cambridge cohort, crude median survival was 3.7 years, compared with 7.0 years for Alzheimer’s. These figures are averages: the course varies widely from one person to another.
Medical disclaimer. The information on this page is provided for informational purposes only and does not constitute medical advice. It does not replace a consultation. Ask a healthcare professional before changing your diet, taking dietary supplements or starting a new practice, especially if you have a medical condition, are pregnant or are under treatment. Dietary supplements do not replace a balanced diet or medical follow-up. Hallucinations, confusion that varies from one hour to the next or repeated falls in an older person warrant a medical consultation. Never start or stop an antipsychotic (neuroleptic) without medical advice.
