A diagnosis of Lewy body dementia requires a progressive decline in your ability to think, as well as two of the following:

  • Fluctuating alertness and thinking (cognitive) function
  • Repeated visual hallucinations
  • Parkinsonian symptoms

One or more of the following features support a Lewy body dementia diagnosis:

  • REM sleep behavior disorder, in which people act out their dreams during sleep
  • Autonomic dysfunction, which involves instability in blood pressure and heart rate, poor regulation of body temperature, sweating, and related symptoms

No single test can diagnose Lewy body dementia. Instead, doctors diagnose your condition through ruling out other conditions that may cause similar signs and symptoms. 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.