What is Lewy Body Dementia?
Lewy Body Dementia (LBD) is a progressive brain disease caused by the buildup of abnormal protein deposits called Lewy bodies — named after the neurologist Friederich Lewy who first described them in 1912. These deposits are made of a protein called alpha-synuclein and accumulate inside brain cells, disrupting the chemicals that control thinking, movement, behavior, and sleep.
LBD is the second most common form of progressive dementia after Alzheimer's disease, affecting an estimated 1.4 million Americans. Despite this, it remains one of the least recognized and most frequently misdiagnosed brain diseases — with nearly 80% of patients initially diagnosed with something else. Many families spend years seeking answers before finally learning the correct name for what their loved one has.
Robin Williams — one of the most beloved performers of his generation — was posthumously diagnosed with diffuse Lewy body disease. His widow, Susan Schneider Williams, has described the disease as "the terrorist inside my husband's brain," and has become one of the most prominent advocates for LBD awareness. His case brought global attention to a disease that millions of families had been struggling with in near-silence.
Lewy Body Dementia is actually an umbrella term covering two related but distinct conditions: Dementia with Lewy Bodies (DLB) and Parkinson's Disease Dementia (PDD). The next section explains the difference — it matters for understanding how the disease will progress and how it should be treated.
Two types — one disease
Both forms of LBD share the same underlying biology — Lewy body protein deposits in the brain — and many of the same symptoms. The key difference is which symptoms appear first and how the disease unfolds over time. Knowing which type a loved one has helps with treatment planning and understanding what to expect.
In DLB, thinking and cognitive problems appear first — or alongside movement problems within the first year. Hallucinations, fluctuating alertness, and cognitive decline are the defining early features. Movement symptoms like rigidity and slow walking develop later. This is the form that most closely resembles Alzheimer's, which is why it is so often misdiagnosed.
In PDD, a person is first diagnosed with Parkinson's disease — with movement symptoms present for at least a year — and later develops significant cognitive decline and dementia. Roughly 50–80% of people with Parkinson's will eventually develop dementia if they live long enough. PDD and DLB are thought to exist on a spectrum of the same underlying disease process.
Clinicians traditionally use the "one-year rule": if dementia develops within one year of movement symptoms beginning, it is called DLB; if dementia develops more than a year after movement symptoms, it is called PDD. While this distinction guides diagnosis, research increasingly shows the two conditions are more similar than different at the biological level.
The four defining features of LBD
LBD has four core clinical features that together make it distinct from Alzheimer's and Parkinson's alone. A diagnosis of probable LBD requires dementia plus at least two of these four features. Recognizing them — especially the ones families often miss — is the first step toward getting the right diagnosis.
One of the most distinctive — and confusing — aspects of LBD. The person's thinking ability and alertness vary dramatically, sometimes hour to hour or day to day. They may seem almost normal one moment and deeply confused the next. Families often describe it as the person "coming and going." These fluctuations are not present in Alzheimer's and are a key diagnostic clue.
Vivid, detailed, and often recurring hallucinations — typically of people, animals, or objects — that are not there. These often appear early in the disease. Unlike psychosis, the person may sometimes recognize that what they're seeing isn't real. These hallucinations are not a sign of psychiatric illness — they are a direct neurological symptom of the disease.
During REM sleep, the brain normally paralyzes the body — preventing us from acting out our dreams. In LBD, this mechanism fails. The person may shout, kick, punch, or leap out of bed during vivid dreams. This symptom often appears years or even decades before other LBD symptoms and is one of the strongest early warning signs of the disease. A bed partner is often the first to notice.
Many — but not all — people with LBD develop movement symptoms similar to Parkinson's disease: slowness, muscle stiffness, a shuffling walk, and a resting tremor. These movement symptoms tend to be milder than in Parkinson's and may not appear until later in the disease. Their presence alongside cognitive symptoms is a strong indicator of LBD.
Beyond these four core features, LBD commonly causes depression, anxiety, autonomic dysfunction (dizziness when standing, constipation, urinary problems), and extreme sensitivity to certain medications. In later stages, memory loss — less prominent early on than in Alzheimer's — becomes more significant.
The disease that hides in plain sight
Lewy Body Dementia is one of the most frequently misdiagnosed diseases in all of medicine. Families spend years — and multiple doctors — searching for answers, while the wrong diagnosis leads to wrong treatments, some of which can be actively dangerous for LBD patients.
The most common misdiagnoses are Alzheimer's disease (more than 50% of cases), Parkinson's disease, and psychiatric conditions like depression or psychosis. LBD mimics all of these so effectively that even experienced neurologists outside specialized memory centers frequently miss it.
The consequences of misdiagnosis go beyond delayed treatment. Because psychiatric symptoms — hallucinations, agitation, confusion — often appear early in LBD, doctors sometimes prescribe antipsychotic medications. In LBD patients, these drugs can trigger severe and potentially fatal reactions. Getting the right diagnosis is not just about understanding — it is a patient safety issue.
LBD overlaps with Alzheimer's (cognitive decline), Parkinson's (movement symptoms), and psychiatric illness (hallucinations and depression) — all at once. No single symptom points clearly to LBD, and the fluctuating nature of the disease means a person may appear normal during a clinic appointment. Additionally, there is currently no single definitive diagnostic test. Diagnosis requires a specialist who knows exactly what to look for.
How to pursue the right diagnosis
Because LBD is so frequently missed, families often need to be proactive advocates. If you recognize the core features described on this page in a loved one — especially fluctuating alertness, visual hallucinations, and acting out dreams — bring this list to a doctor and specifically ask about Lewy Body Dementia. Requesting a specialist referral is essential.
Ask for a referral to a behavioral neurologist or a memory disorder specialist at an academic medical center. General practitioners and even many general neurologists are not trained to recognize LBD. The Lewy Body Dementia Association's helpline (1.800.LBDA.INFO) can help families find an LBD specialist near them.
A specialist will evaluate cognition, movement, sleep history, and psychiatric symptoms. Critically, they will ask specifically about the four core features: fluctuating alertness, hallucinations, REM sleep behavior disorder, and Parkinsonism. Bring a family member who can describe symptoms they've observed at home — especially sleep behavior.
If REM sleep behavior disorder is suspected, a sleep study can confirm it. This is one of the most objective diagnostic tools available for LBD and can help distinguish it from Alzheimer's, which does not cause REM sleep behavior disorder.
MRI can rule out other causes of dementia. A specialized scan called a DaTscan detects loss of dopamine-producing neurons — a hallmark of LBD — and helps distinguish it from Alzheimer's. A DaTscan that shows reduced dopamine activity is considered a strong indicator of LBD or Parkinson's.
Blood tests rule out other causes of dementia symptoms — thyroid disease, vitamin deficiencies, and infections. This step is important even when LBD is suspected, as some patients have multiple overlapping conditions.
Some medications can cause symptoms that mimic LBD — particularly antipsychotics and certain anti-nausea drugs. A specialist will carefully review all current medications to identify any that may be contributing to or masking the true picture.
What helps — and what can cause serious harm
There is no cure for LBD, and no treatments that slow or stop its progression. Treatment focuses on managing the specific symptoms that are most affecting quality of life. However, LBD has a unique and critical medication danger that every family and every treating physician must know about before any drug is prescribed.
Approximately 50% of people with LBD have severe, potentially fatal reactions to antipsychotic medications — including some of the most commonly prescribed drugs for hallucinations and agitation. These reactions can include sudden severe worsening of Parkinsonism, profound sedation, high fever, muscle rigidity, and death. This is called neuroleptic sensitivity and it is one of the most dangerous and underappreciated aspects of LBD. Even "atypical" antipsychotics considered safer in Alzheimer's can be dangerous in LBD. Every family member and every doctor treating someone with LBD must know this before any medication for hallucinations or agitation is prescribed. If your loved one is being prescribed an antipsychotic, ask their neurologist first.
The same drugs used in Alzheimer's — donepezil, rivastigmine — can meaningfully reduce hallucinations and improve thinking in LBD patients. Unlike in Alzheimer's, these drugs can have a more dramatic positive effect in LBD, sometimes significantly reducing distressing hallucinations. Generally well tolerated.
Levodopa — the primary Parkinson's drug — can help with movement symptoms in LBD. However, it must be used carefully: it can worsen hallucinations and confusion in some patients. Starting at a low dose with gradual increases, under close specialist supervision, is essential.
Low-dose clonazepam or melatonin can reduce the dangerous acting-out behavior during sleep. This protects both the patient and their bed partner from injury. Bed safety modifications — mattress on the floor, padding — are also important practical steps.
Physical therapy addresses movement problems and fall prevention. Occupational therapy helps adapt the home and daily routines as the disease progresses. Speech therapy addresses swallowing difficulties and communication changes. All three are strongly recommended and highly effective for maintaining quality of life.
Our Disease Guides hub includes a full side-by-side comparison of all three diseases — including symptoms, brain changes, and how they overlap. View the full comparison →
Caregiving for LBD — what you need to know
Caring for someone with Lewy Body Dementia is among the most demanding caregiving experiences — not because the person is more difficult to love, but because the disease is so unpredictable and so frequently misunderstood by the medical system itself. Caregivers often find themselves educating doctors about the disease their loved one has.
The fluctuating nature of LBD is particularly exhausting — a loved one may be lucid and conversational one morning and barely recognizable by afternoon. This variability can make caregivers doubt their own observations and feel isolated in their experience. The LBD community is an invaluable source of support and validation.
Carry a medication warning card. Because antipsychotic sensitivity is so dangerous — and so unknown to non-specialist doctors — the LBDA provides a wallet card that LBD patients can carry warning medical providers about this risk. This is especially critical during emergency room visits or hospital stays.
Make the sleep environment safe. REM sleep behavior disorder causes people to physically act out dreams — sometimes violently. Remove sharp objects from the bedroom, consider a mattress on the floor, and use bed rails or padding to prevent falls and injury to both the person and their bed partner.
Don't argue with hallucinations. If the person is not distressed by a hallucination, there is no need to correct them. If they are frightened, calmly redirect their attention. Arguing or insisting the hallucination isn't real rarely helps and often increases distress.
Find an LBD specialist. General neurologists often lack deep LBD expertise. An academic medical center with a memory disorders clinic or movement disorder specialist is the best option. The LBDA helpline can help you find one.