Inside Look: How Doctors Diagnose Lewy Body Dementia

Lewy body dementia (LBD) is a progressive neurodegenerative disorder that ranks as the second or third most common type of dementia worldwide, making up approximately 20 to 30 percent of dementia cases. But diagnosing LBD is challenging, in part because its symptoms overlap with both Parkinson’s and Alzheimer’s disease. 

Unlike Alzheimer’s, where brain imaging, blood tests, and sometimes lumbar punctures may help confirm the diagnosis, LBD cannot be definitively diagnosed in living individuals. Instead, clinicians rely on detailed medical history, symptom evaluation, and a collection of clinical features and biomarkers.

Why LBD is often missed, or misdiagnosed

• Symptom overlap
  Core LBD symptoms like hallucinations, cognitive fluctuations, REM sleep behavior disorder (RBD), and parkinsonism may mimic Alzheimer’s, Parkinson’s, or psychiatric disorders. Up to half of LBD cases may be misdiagnosed in clinical settings.  
• Lack of objective biomarkers
  While research is advancing, there is still no universally accepted biomarker for LBD in routine clinical use. That said, emerging tools may enhance early detection. 

The diagnosis relies on a doctor’s evaluation of your medical history and symptoms. 

“The most important thing is to talk carefully with a patient and carer who knows the patient and discuss what symptoms they have experienced,” Dr. Dag Aarsland, a leading LBD and Parkinson’s researcher from King’s College in London, told Being Patient. 

While some additional biomarker tests are available, a doctor might make their diagnosis based on the clinical evaluation alone.

How doctors diagnose Lewy body dementia

Doctors use a set of criteria developed in 2017 but the Dementia with Lewy Bodies Consortium to decide whether someone has LBD. Based on the number of symptoms and criteria a patient presents with, a doctor might make a “probable” or “possible” diagnosis. 

Core features

Doctors first look for hallmark symptoms of LBD. The first three of these symptoms often occur early and persist throughout the disease. 

• Cognitive fluctuations: Changes in cognitive ability, attention, alertness, or concentration that vary day-to-day. 
• Frequent, well-formed visual hallucinations: Seeing people, animals, or objects that aren’t there. 
• REM sleep behavior disorder: Acting out dreams while asleep. For people who sleep with a spouse, these sudden and sometimes violent movements may wake them.
• Symptoms of Parkinsonism: Slow movements, muscle stiffness, tremors or trouble walking. 

Supportive clinical features

These symptoms could help doctors decide on a diagnosis if someone only has one of the core clinical features. These symptoms include:

• severe side effects or sensitivity to antipsychotic drugs
• problems with posture
• repeated falls
• sleep problems
• problems with automatic body processes, like sleep and bowel movements
• delusions, apathy, anxiety, or depression

Indicative biomarkers

These brain and heart scans, and sleep tests, help doctors look for other signs of LBD.

• Dopamine transporter scans (DAT-SPECT or DAT-PET): These brain scans measure the levels of the neurotransmitter dopamine in the brain. Low levels in certain brain regions may be a sign of LBD. 
• Heart nerve imaging (MIBG scan): This scan uses a radioactive tracer to see how well the heart’s nerves are working. If too little of the tracer is taken up by the nerve cells, it might indicate LBD. 
• Sleep studies (polysomnography): These studies help confirm REM sleep behavior disorder. 

Supportive biomarkers

These brain scans and imaging tests can help doctors gain more certainty about a diagnosis. 

• CT or MRI brain scan: These tests could help differentiate between Alzheimer’s and LBD. In LBD, the brain’s memory centers are intact, while in Alzheimer’s, they are shrinking and dying. 
• FDG-PET and other tests of brain metabolism: If these tests show that the brain is using less energy than normal, it is a potential sign of LBD.
• Electroencephalography (EEG) to measure brain waves: Abnormalities measured by this test might be a sign of LBD.

Ruling out other diseases

When doctors take a medical history, clinical examinations, and run different blood tests to help rule out other conditions like low levels of thyroid hormones or B12 deficiency, that cause similar symptoms. 

There are lots of overlaps in symptoms with Alzheimer’s, but the timing of the symptoms could provide an additional clue. For example, Aarsland said, early hallucinations often suggest LBD over Alzheimer’s. 

“Hallucinations in a person with very early dementia or even before dementia should make doctors suspicious that the patient does not have Alzheimer’s disease, but Lewy body disease,” Aarsland said.

While ruling out diseases is important, doctors also recognize that some forms of dementia often co-occur. Many people develop mixed forms of dementia and may have Alzheimer’s alongside LBD. 

Making the diagnosis: Probable vs. possible Lewy body dementia

• Probable LBD: At least two core clinical features, even in the absence of biomarkers.
• Possible LBD: One core clinical feature plus supportive biomarkers, or biomarkers alone without clear core features.

Emerging biomarkers: What’s on the horizon?

Promising biomarkers under investigation include:

• Alpha-synuclein detection in cerebrospinal fluid
• Skin biopsy assays
  These may enable diagnosis in earlier stages—which could significantly impact treatment strategies in the future. 

Why early and accurate diagnosis matters

• Treatment implications: LBD patients are especially sensitive to antipsychotics, which may severely worsen symptoms. Accurate diagnosis guides safer medication choices, such as cholinesterase inhibitors that may help with cognitive and hallucination symptoms. Alzheimer’s AssociationWikipedia
• Care planning: Awareness of symptoms—like sleep issues or autonomic dysfunction—helps caregivers plan effectively and reduces risks. Medicine Today
• Research and future therapies: Better diagnostic tools fuel clinical trials, including those seeking disease-modifying treatments. 

Ready to go deeper? Learn more about the difference between LDB and Alzheimer’s.