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
- 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, supports a Lewy body dementia diagnosis.
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:
- Muscle tone
- Eye movements
- 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 of a similar age and education level. This can help distinguish normal from abnormal cognitive aging, and may help diagnose the condition.
These can rule out physical problems that can affect brain function, such as vitamin B-12 deficiency or an underactive thyroid gland.
Your doctor may order an MRI 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 medical history and physical examination, certain features on imaging studies can suggest different types of dementia, such as Alzheimer's or Lewy body dementia.
Most of the time, you won't need more brain scans. If the diagnosis is unclear or the signs and symptoms aren't typical, your doctor may suggest some additional imaging tests, including these that can support a diagnosis of Lewy body dementia:
- Fluorodeoxyglucose PET brain scans, which can assess brain function.
- Single-photon emission computerized tomography (SPECT) or PET imaging, which can determine whether dopamine transporter uptake is reduced in the brain.
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.
Your doctor may also order a heart test called myocardial scintigraphy to check the blood flow to your heart, which can be a sign of Lewy body dementia.