It’s important to know which type of LBD a person has, both to tailor treatment to particular symptoms and to understand how the disease will likely progress. Clinicians and researchers use the “1-year rule” to diagnose which form of LBD a person has. If cognitive symptoms  appear within a year of movement problems, the diagnosis is dementia with Lewy bodies. If cognitive problems develop more than a year after the onset of movement problems, the diagnosis is Parkinson’s disease dementia.
Regardless of the initial symptoms, over time people with LBD often develop similar symptoms due to the presence of Lewy bodies  in the brain. But there are some differences. For example, dementia with Lewy bodies may progress more quickly than Parkinson’s disease dementia.
Dementia with Lewy bodies is often hard to diagnose because its early symptoms may resemble those of Alzheimer’s,  Parkinson’s disease, or a psychiatric illness. As a result, it is often misdiagnosed or missed altogether. As additional symptoms appear, it is often easier to make an accurate diagnosis.
The good news is that doctors are increasingly able to diagnose LBD  earlier and more accurately as researchers identify which symptoms help distinguish it from similar disorders.
Difficult as it is, getting an accurate diagnosis of LBD early on is important so that a person:
While a diagnosis of LBD can be distressing, some people are relieved to know the reason for their troubling symptoms. It is important to allow time to adjust to the news. Talking about a diagnosis can help shift the focus toward developing a care plan.
Many physicians and other medical professionals are not familiar with LBD, so patients may consult several doctors before receiving a diagnosis. Visiting a family doctor is often the first step for people who are experiencing changes in thinking, movement, or behavior. However, neurologists—doctors who specialize in disorders of the brain and nervous system—generally have the expertise needed to diagnose LBD. Geriatric psychiatrists, neuropsychologists, and geriatricians may also be skilled in diagnosing the condition.
If a specialist cannot be found in your community, ask the neurology department of the nearest medical school for a referral. A hospital affiliated with a medical school may also have a dementia or movement disorders clinic that provides expert evaluation. See the Resources  section.
Doctors perform physical and neurological examinations and various tests to distinguish LBD from other illnesses. An evaluation may include:
There are no brain scans or medical tests that can definitively diagnose LBD. Currently, LBD can be diagnosed with certainty only by a brain autopsy after death.
However, researchers are studying ways to diagnose LBD more accurately in the living brain. Certain types of neuroimaging—positron emission tomography and single-photon emission computed tomography—have shown promise in detecting differences between dementia with Lewy bodies and Alzheimer’s disease. These methods may help diagnose certain features of the disorder, such as dopamine deficiencies. Researchers are also investigating the use of lumbar puncture  (spinal tap) to measure proteins in cerebrospinal fluid that might distinguish dementia with Lewy bodies from Alzheimer’s disease and other brain disorders.
It is important for the patient and a close family member or friend to tell the doctor about any symptoms involving thinking, movement, sleep, behavior, or mood. Also, discuss other health problems and provide a list of all current medications , including prescriptions, over-the-counter drugs, vitamins, and supplements. Certain medications can worsen LBD symptoms.
Caregivers may be reluctant to talk about a person’s symptoms when that person is present. Ask to speak with the doctor privately if necessary. The more information a doctor has, the more accurate a diagnosis can be.