Lewy body dementia (LBD) is an umbrella term for two related conditions — dementia with Lewy bodies and Parkinson's disease dementia — both caused by abnormal clumps of a protein called alpha-synuclein, known as Lewy bodies, building up in the brain. The National Institute of Neurological Disorders and Stroke identifies this protein buildup as the defining feature that separates LBD from Alzheimer's disease, which involves a different pair of brain changes entirely. Alzheimer's disease is driven primarily by amyloid plaques and tau tangles, while LBD stems from Lewy bodies — though the two conditions overlap more than their separate names suggest. The Alzheimer's Association's clinical guidance notes that many people with LBD also carry the plaques and tangles typical of Alzheimer's, which is one reason the two conditions are frequently confused or misdiagnosed.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- What Causes Lewy Body Dementia?
- How Do the Early Symptoms Differ From Alzheimer's?
- Why Is Lewy Body Dementia Often Misdiagnosed?
- Why Does Getting the Right Diagnosis Matter for Treatment?
- Frequently Asked Questions
What Causes Lewy Body Dementia?
Lewy body dementia results from deposits of alpha-synuclein protein that form inside neurons, disrupting how brain cells communicate and eventually causing them to die off. These deposits, called Lewy bodies, tend to collect in regions that control thinking, movement, behavior, and sleep, which explains why LBD produces such a wide mix of symptoms compared with Alzheimer's. According to the Lewy Body Dementia Association, LBD affects approximately 1.4 million people in the United States, most often appearing after age 50.
That makes it the second most common form of degenerative dementia after Alzheimer's disease, though it remains far less familiar to the public and, at times, to clinicians. The two diagnoses under the LBD umbrella — dementia with Lewy bodies and Parkinson's disease dementia — are distinguished mainly by sequence. If cognitive decline appears before or within a year of movement problems, doctors generally call it dementia with Lewy bodies; if movement symptoms came first and dementia developed later, it's classified as Parkinson's disease dementia.
How Do the Early Symptoms Differ From Alzheimer's?
Alzheimer's disease almost always announces itself through memory loss — forgetting recent conversations, misplacing items, or repeating questions. Lewy body dementia takes a different path. The LBDA's clinical fact sheet reports that LBD often begins with visuospatial problems (trouble judging distance or navigating familiar spaces), fluctuating attention and alertness, and difficulty with executive function — planning, organizing, and problem-solving.
Memory loss in LBD tends to show up later in the disease course, not at the start. This difference matters for families trying to make sense of early changes. Someone with LBD may seem sharp in conversation one afternoon and noticeably confused or drowsy the next, a pattern of fluctuation that is far less typical of early Alzheimer's. A few other early distinctions are worth watching for:.
- Visual hallucinations appear in about 80% of people with dementia with Lewy bodies, usually early in the illness, compared with about 20% of Alzheimer's cases — and in Alzheimer's, hallucinations typically don't appear until the disease is moderately advanced, according to MSD Manuals' clinical comparison.
- REM sleep behavior disorder — acting out dreams physically during sleep — affects roughly half of people with LBD, per the Alzheimer's Association, and can show up years before any cognitive symptoms. This sleep disorder is rare in Alzheimer's.
- Movement changes — slowness, stiffness, shuffling gait, tremor — are common in LBD but rare in Alzheimer's, NINDS notes, often alongside autonomic problems like blood pressure drops and dizziness when standing.
Why Is Lewy Body Dementia Often Misdiagnosed?
Neither Alzheimer's nor LBD can be confirmed with certainty while a patient is alive. The NINDS and University of Michigan both note that diagnosis during life relies on symptom patterns, neurological exams, and brain imaging to rule out other causes. A definitive answer only comes from an autopsy that finds Lewy bodies or Alzheimer's-type plaques and tangles in brain tissue.
That diagnostic uncertainty, combined with symptom overlap, makes LBD one of the more frequently missed or delayed dementia diagnoses. A person with early visual hallucinations and fluctuating alertness but intact memory may not fit the pattern a clinician expects from Alzheimer's, and the reverse is also true: someone whose LBD has advanced enough to affect memory may be mistaken for a straightforward Alzheimer's case. Families and caregivers can help narrow the picture by tracking the order in which symptoms appeared, any history of acting out dreams during sleep, episodes of visual hallucinations, and whether alertness noticeably rises and falls through the day or week. Bringing a written symptom timeline to a neurology appointment can speed up an accurate diagnosis.
Why Does Getting the Right Diagnosis Matter for Treatment?
Getting the diagnosis right has immediate, practical consequences — most urgently around medication safety. The LBDA's emergency-room guidance warns that 25% to 50% of people with LBD who are given standard doses of antipsychotic (neuroleptic) medications develop a severe sensitivity reaction. This can include worsening cognition, heavy sedation, or a neuroleptic-malignant-syndrome-like state that can be fatal.
Anyone with LBD who needs emergency care should make sure clinicians know the diagnosis before any antipsychotic is prescribed. On the treatment side, there is currently no drug approved specifically for LBD. The Alzheimer's Association notes that cholinesterase inhibitors approved for Alzheimer's — such as donepezil and rivastigmine — are often used off-label for LBD, and some evidence suggests LBD may respond to them as well as, or better than, Alzheimer's does. A few practical steps follow from this:.
- Carry a card or alert noting the LBD diagnosis in case of an emergency room visit, specifically flagging antipsychotic sensitivity.
- Ask a neurologist experienced with LBD (rather than only Alzheimer's) about cholinesterase inhibitors, since response patterns can differ.
- Expect any new medication, including those for unrelated conditions, to be checked against the antipsychotic-sensitivity risk before it's started.
Frequently Asked Questions
Can someone have both Lewy body dementia and Alzheimer's at the same time?
Yes. The Alzheimer's Association notes that many people with LBD also have the amyloid plaques and tau tangles characteristic of Alzheimer's, which is part of why distinguishing the two conditions clinically is difficult.
Is Lewy body dementia the same as Parkinson's disease dementia?
They fall under the same umbrella but aren't identical. Per NINDS, the distinction depends on timing: if dementia appears before or close to the onset of movement symptoms, it's called dementia with Lewy bodies; if movement symptoms came first by more than a year, it's classified as Parkinson's disease dementia.
Why can't doctors confirm Lewy body dementia with a test while someone is alive?
Both LBD and Alzheimer's can only be confirmed with certainty through an autopsy examining brain tissue for Lewy bodies or plaques and tangles, according to NINDS and University of Michigan. While living, diagnosis relies on symptom patterns, neurological exams, and imaging used to rule out other causes.
