A progressive decline in your ability to think is required to diagnose Lewy body dementia.

In addition, two of the following core symptoms must be present:

  • Fluctuating and unpredictable alertness and thinking (cognitive) function
  • Repeated visual hallucinations
  • Parkinsonian symptoms
  • REM sleep behavior disorder, in which people act out their dreams during sleep

In addition to the core symptoms of Lewy body dementia, tests for certain biomarkers can further support a diagnosis of Lewy body dementia. Biomarkers are substances in the blood that indicate the presence of a disease, such as Lewy body dementia.

Right now there are no biomarkers to definitively diagnose Lewy body dementia, but some biomarkers support it. Biomarkers alone, without symptoms, aren't enough for a diagnosis. Biomarker tests to support Lewy body dementia diagnosis include:

  • Nuclear imaging tests such as single-photon emission computerized tomography (SPECT) and positron emission tomography (PET)
  • Tests that measure check nerve function of the heart's blood vessels (iodine-MIBG myocardial scintigraphy)
  • Sleep studies that examine brain wave activity

Your doctor may also diagnose Lewy body dementia based on the presence of one core symptom and one or more of these biomarkers that support the diagnosis:

  • Autonomic dysfunction, which involves instability in blood pressure and heart rate, poor regulation of body temperature, sweating, and related symptoms
  • Feeling excessively sleepy during the daytime
  • Loss of the sense of smell

There are several combinations of symptoms, features and biomarkers that help doctors diagnose Lewy body dementia. Depending on the combination, the diagnosis may be considered probable or possible.

Doctors may also try to rule out other conditions that may cause similar signs and symptoms to support a diagnosis of Lewy body dementia. Tests may include:

Neurological and physical examination

Your doctor may check for signs of Parkinson's disease, strokes, tumors or other medical conditions that can affect the brain and physical function. The neurological examination may test:

  • Reflexes
  • Strength
  • Walking
  • Muscle tone
  • Eye movements
  • Balance
  • Sense of touch

Assessment of mental abilities

A short form of this test, which assesses your memory and thinking skills, can be done in less than 10 minutes in your doctor's office. It's not generally useful in distinguishing Lewy body dementia from Alzheimer's disease but can indicate dementia. Longer tests can take several hours, but help identify Lewy body dementia.

Your doctor will compare your test results with those of people from a similar age and education level. This can help distinguish normal from abnormal cognitive aging, and may help diagnose the condition.

Blood tests

These can rule out physical problems that can affect brain function, such as vitamin B-12 deficiency or an underactive thyroid gland.

Brain scans

Your doctor may order an MRI, PET or CT scan to identify a stroke or bleeding, and to rule out the possibility of a tumor. While dementias are diagnosed based on the history and physical examination, certain features on imaging studies can suggest different types of dementia, such as Alzheimer's or Lewy body dementia.

Your doctor may order a sleep evaluation to check for REM sleep behavior disorder or an autonomic function test to look for signs of heart rate and blood pressure instability.