The essentials

Lewy body dementia is a brain disease caused by clumps of a protein, alpha-synuclein. Its signature: changing alertness, vivid visual hallucinations, acting out dreams and Parkinson-like stiffness. No routine blood test shows Lewy bodies: blood tests rule out treatable causes, then clinical criteria and sometimes scans confirm the picture. Some antipsychotics can cause severe reactions, so the diagnosis matters.

What is Lewy body dementia, at a glance?

"Lewy body dementia" covers two closely related conditions: dementia with Lewy bodies (DLB) and Parkinson's disease dementia[3]. Both involve the same protein deposits, Lewy bodies. Timing separates them: when thinking problems start before, or within a year of, movement problems, it is DLB; when dementia appears in someone with well-established Parkinson's disease, it is Parkinson's disease dementia[1].

Lewy body dementia in brief
TopicKey facts
Other namesLewy body disease; "major neurocognitive disorder with Lewy bodies" in the DSM-5[1]
How commonAbout 1.4 million people in the United States; about 5% of dementia in older adults, second after Alzheimer's disease among degenerative dementias[4]. Often missed: 4.2% of dementias diagnosed in the community, 7.5% in specialist clinics[5]
Usual ageUsually starts between 50 and 85[4]
Key testsClinical criteria (McKeith 2017); DaTscan, MIBG heart scan, sleep study; blood tests to exclude other causes
Main specialistsNeurologist, geriatric psychiatrist or memory clinic

What are the symptoms of Lewy body dementia?

Unlike in Alzheimer's disease, memory often holds up at first; attention, planning and judging distances are hit earlier[1][4]. The 2017 international criteria name four core features[1]:

  • Common Fluctuations: good hours or days alternate with confusion, staring into space, drowsiness or muddled speech.
  • Common Visual hallucinations that recur, detailed, often of people or animals[4].
  • Common REM sleep behavior disorder: shouting or kicking while dreaming, sometimes years before any thinking problem[1][4].
  • Common Parkinsonism: slow movements, stiffness, a shuffling walk, sometimes a resting tremor[1].
  • Possible Body signals: dizziness or fainting on standing, constipation, bladder problems, loss of smell, heavy daytime sleepiness, repeated falls[1]. See low blood pressure and its tests.
  • Possible Mood and beliefs: depression, anxiety, apathy or fixed false beliefs[1].
  • Rare Severe reaction to an antipsychotic as the first warning sign, after a medicine given for agitation[1][6].

Why the antipsychotic warning matters

In a study with diagnoses confirmed after death, 81% of patients with Lewy body dementia given an older antipsychotic reacted badly and 54% severely, with higher mortality the following year[6]. Guidelines warn that antipsychotics can worsen movement and cause severe sensitivity reactions in this disease[2]. Mention the diagnosis before any hospital stay or surgery.

When should I see a doctor?

When to see a doctor

  • Emergency: call 911 for a fall with a head injury, fainting, choking, sudden weakness on one side or trouble speaking, or high fever with severe stiffness and confusion after a new medicine, especially an antipsychotic[2][6].
  • Within 24 to 48 hours if confusion worsens suddenly, hallucinations change after a new medicine, or with burning urination or fever: a sudden change is more often delirium (infection, medicine, dehydration) than the disease itself[2].
  • At your next appointment if you notice acting out dreams, repeated visual hallucinations, alertness that varies from day to day, new slowness or stiffness, or unexplained falls.

What causes Lewy body dementia, and who is at risk?

Alpha-synuclein, a normal nerve-cell protein, misfolds into clumps (Lewy bodies) that disrupt acetylcholine, needed for attention, and dopamine, needed for movement[1][4]. Why it starts is mostly unknown.

  • Age is the main risk factor: most people are diagnosed after 50[4].
  • Genes: rare changes in the SNCA or SNCB genes can cause the disease; variants in GBA1 and the APOE e4 version raise the risk without causing it on their own[4].
  • REM sleep behavior disorder is a strong early warning sign[1].
  • Alzheimer changes are often present in the same brain, which can blur the symptoms[1].

To compare it with other forms, see the types of dementia.

How is Lewy body dementia diagnosed, and can a blood test show it?

There is no single test. A specialist combines the history from patient and family, a neurological examination, thinking tests and selected scans[1][2].

Step 1: blood tests to rule out other causes

Guidelines first ask doctors to look for reversible causes of confusion: delirium, depression, poor sight or hearing, anticholinergic medicines[2]. The American Academy of Neurology recommends screening for vitamin B12 deficiency, an underactive thyroid and depression[7]. These tests do not detect Lewy bodies; they look for another, treatable problem.

Fictitious example of a lab report (United States format), man aged 76 with confusion and visual hallucinations
TestResultReference rangeFlag
Vitamin B12, serum245 pg/mL299-1054 pg/mLL
TSH2.1 µU/mL0.4-4.8 µU/mL
Sodium138 mEq/L135-145 mEq/L
RPR (syphilis screen)NonreactiveNonreactive
  1. Vitamin B12 245 pg/mL, flag L: below 299 pg/mL is a possible sign of deficiency; doctors usually confirm it with methylmalonic acid[10]. It needs treatment, but it does not explain hallucinations and dream enactment: the search continues.
  2. TSH normal: 0.4 to 4.8 µU/mL is the usual range; some labs accept higher values in older adults[11].
  3. Sodium normal: within 135 to 145 mEq/L[12].
  4. RPR nonreactive: a yes/no result, so no H or L flag. Your laboratory's own ranges always apply.

Normal blood tests but symptoms that do not fit? BloodSense explains every line of your report, from B12 to TSH, so you know what has been ruled out before seeing the specialist.

Get my blood results explained

Step 2: clinical criteria

The 2017 consensus (McKeith criteria) is the reference[1]. "Probable" DLB means dementia plus at least 2 core features, or 1 core feature plus at least 1 indicative test. "Possible" DLB means only 1 core feature or only 1 indicative test. A test alone is never enough.

The indicative tests in the 2017 criteria
TestWhat it looks atResult that points to Lewy bodies
DaTscan (dopamine transporter SPECT or PET)Dopamine nerve endings in the brainReduced uptake in the basal ganglia
MIBG heart scan (myocardial scintigraphy)The nerves of the heartLow uptake
Sleep study (polysomnography)Muscle tone during dream sleepREM sleep without the normal muscle relaxation

A normal DaTscan or MIBG scan does not rule the disease out[2]. MRI or CT mainly excludes stroke or a tumor; well-preserved memory areas on MRI support the diagnosis[1].

Step 3: the new alpha-synuclein tests

Two newer tests look for the abnormal protein itself. A seed amplification assay (RT-QuIC) on spinal fluid detected Lewy body diseases with 95.3% sensitivity and 98% specificity[8]. A small skin biopsy found phosphorylated alpha-synuclein in 96% of people with DLB and in 3.3% of people without a synuclein disease[9]. Both are promising but not yet in the official criteria, and were studied in people already clearly diagnosed[9]. A positive result shows the protein, not which disease or how fast it will progress. There is no validated routine blood test for alpha-synuclein yet.

Which tests are used to follow Lewy body dementia?

No blood marker tracks the disease. Follow-up relies on symptoms, the family's observations and daily-function scales such as the BADLS scale.

  • Visits: thinking, movement, sleep, mood and falls, sooner after any change.
  • Blood pressure lying and standing, to catch a drop on standing that causes falls[1][3].
  • Heart rate with cholinesterase inhibitors, which can slow the pulse[3].
  • Repeat blood and urine tests when things change suddenly: to find pain, infection, dehydration or a medicine effect[2]. A low B12 is rechecked after treatment.

How is Lewy body dementia treated?

There is no cure. Each symptom is treated, and a medicine that helps one can worsen another, so changes are made one at a time[3]. No doses are given here.

  • Thinking, alertness and hallucinations: cholinesterase inhibitors (donepezil or rivastigmine) are offered first; memantine is an option if they are not tolerated[2].
  • Movement: levodopa can help stiffness and slowness but may increase hallucinations, so doctors use the lowest useful dose[3].
  • Distressing hallucinations or agitation: look for a trigger and use non-drug approaches first; antipsychotics only for severe distress or danger, with great caution[2].
  • Sleep, blood pressure, bowel and mood: treated as in Parkinson's disease[3].
  • Therapies: physical, occupational and speech therapy, exercise, and support for carers[3].

How can we live with Lewy body dementia day to day?

People typically live about 5 to 7 years after diagnosis, with wide variation[4]. Nothing proven prevents it, but daily habits reduce risks.

  • Carry a card or note saying "suspected Lewy body dementia: antipsychotic sensitivity" for emergencies and hospital stays[6].
  • Bring the full medicine list to each visit: some sleep aids and bladder pills worsen confusion[2].
  • Make the bedroom safe if dreams are acted out.
  • Stand up slowly, drink enough and keep lighting good to limit falls.
  • Do not argue about harmless hallucinations; calm reassurance works better.
  • Plan ahead early: legal and care decisions are easier while the person can still take part in them[2].

Questions to ask your doctor

  1. Which core features of Lewy body dementia do you see, and is it "probable" or "possible"?
  2. Have my blood tests ruled out B12 deficiency, thyroid problems and other treatable causes?
  3. Would a DaTscan, MIBG scan or sleep study change my care?
  4. Which medicines should I avoid, and what should I tell an emergency team?
  5. How do we tell a flare of confusion from an infection or delirium?

Frequently asked questions

What is the difference between Lewy body dementia and Alzheimer's disease?

Alzheimer's disease usually starts with memory loss. Lewy body dementia more often starts with fluctuations, hallucinations, dream enactment or stiffness[1][4]. The two can coexist in the same person.

Can Lewy body dementia cause aggression?

It can. Frightening hallucinations, false beliefs or a confused moment can lead to agitation. A sudden change should first prompt a check for pain, infection or a new medicine[2].

My father acts out his dreams. Will he get dementia?

Not necessarily, but REM sleep behavior disorder is a recognized early sign of Lewy body diseases[1]. It deserves a sleep study and regular follow-up with a neurologist.

  1. McKeith IG, Boeve BF, Dickson DW, et al. Diagnosis and management of dementia with Lewy bodies: Fourth consensus report of the DLB Consortium. Neurology. 2017;89(1):88-100. doi:10.1212/WNL.0000000000004058 (accessed November 7, 2026)
  2. National Institute for Health and Care Excellence (NICE). Dementia: assessment, management and support for people living with dementia and their carers. NICE guideline NG97. June 2018. nice.org.uk (accessed November 7, 2026)
  3. Taylor JP, McKeith IG, Burn DJ, et al. New evidence on the management of Lewy body dementia. Lancet Neurol. 2020;19(2):157-169. doi:10.1016/S1474-4422(19)30153-X (accessed November 7, 2026)
  4. MedlinePlus Genetics. Dementia with Lewy bodies. US National Library of Medicine. medlineplus.gov (accessed November 7, 2026)
  5. Vann Jones SA, O'Brien JT. The prevalence and incidence of dementia with Lewy bodies: a systematic review of population and clinical studies. Psychol Med. 2014;44(4):673-683. doi:10.1017/S0033291713000494 (accessed November 7, 2026)
  6. McKeith I, Fairbairn A, Perry R, Thompson P, Perry E. Neuroleptic sensitivity in patients with senile dementia of Lewy body type. BMJ. 1992;305(6855):673-678. doi:10.1136/bmj.305.6855.673 (accessed November 7, 2026)
  7. Knopman DS, DeKosky ST, Cummings JL, et al. Practice parameter: diagnosis of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2001;56(9):1143-1153. doi:10.1212/WNL.56.9.1143 (accessed November 7, 2026)
  8. Rossi M, Candelise N, Baiardi S, et al. Ultrasensitive RT-QuIC assay with high sensitivity and specificity for Lewy body-associated synucleinopathies. Acta Neuropathol. 2020;140(1):49-62. doi:10.1007/s00401-020-02160-8 (accessed November 7, 2026)
  9. Gibbons CH, Levine T, Adler C, et al. Skin biopsy detection of phosphorylated α-synuclein in patients with synucleinopathies. JAMA. 2024;331(15):1298-1306. doi:10.1001/jama.2024.0792 (accessed November 7, 2026)
  10. MedlinePlus Medical Encyclopedia. Vitamin B12 level. US National Library of Medicine. medlineplus.gov (accessed November 7, 2026)
  11. MedlinePlus Medical Encyclopedia. TSH test. US National Library of Medicine. medlineplus.gov (accessed November 7, 2026)
  12. MedlinePlus Medical Encyclopedia. Sodium blood test. US National Library of Medicine. medlineplus.gov (accessed November 7, 2026)

This page is general information. It does not replace the advice of a doctor, who makes the diagnosis from symptoms, examination and tests; no blood test alone can confirm or rule out Lewy body dementia.