DEAR MAYO CLINIC: What’s the difference between Lewy body dementia and Alzheimer’s? How is Lewy body dementia diagnosed?

ANSWER: Doctors diagnose Lewy body dementia based on the range of symptoms a person shows. Generally, the diagnosis requires an ongoing decline in thinking skills, along with two of the following: visual hallucinations, Parkinsonism or fluctuating alertness. In addition, people who have Lewy body dementia also may experience a sleep condition known as REM sleep behavior disorder, in which people act out their dreams while they sleep. They also may have instability in their blood pressure and heart rate, and the body may have difficulty controlling body temperature and sweating.

A brain disease that gets worse over time, Lewy body dementia is caused by an abnormal protein, called synuclein, which is deposited in certain nerve cells and nerve processes. These deposits are called Lewy bodies — named after the physician who first identified them. In Lewy body dementia, Lewy bodies are found in the deep structures of the brain that control movement, as well as in the middle and outer structures involved in emotion, behavior, judgment and awareness.

Many patients with Lewy body dementia also have overlapping Alzheimer’s disease. About half of Lewy body patients have significant Alzheimer’s disease, as well. Thus, it is not surprising that those diagnosed with Lewy body dementia have symptoms associated with Alzheimer disease, such as memory loss and naming difficulty. However, when doctors who have expertise and experience with the disease make a Lewy body dementia diagnosis, that diagnosis is often correct — as confirmed later during an autopsy. An accurate diagnosis is important, because Lewy body dementia responds differently than Alzheimer’s disease to commonly prescribed dementia medications.

Lewy body dementia usually progresses gradually over several years, but the way it progresses can vary significantly from person to person. For example, Lewy body dementia may begin with signs of dementia, and Parkinsonism appears later. Or the disease may start with movement difficulties, and signs of dementia don’t emerge for some time. Most people with Lewy body dementia experience the onset of Parkinsonism and dementia within one year. As Lewy body dementia progresses, all symptoms usually become more severe.

Hallucinations occur early in Lewy body dementia but only after about four years in Alzheimer’s disease. If a person acts out dreams, that is strong evidence that he or she has synuclein protein in the brain. This protein is found only in Lewy body dementia, Parkinson’s disease and a rare disease called multiple system atrophy. Acting out one’s dreams is a feature in all of these diseases.

Lewy body dementia is a complex disease, and it can be difficult to control. Currently, there’s no cure. But, when treatment is carefully managed, symptoms may be reduced, so they have less effect on a person’s daily functioning and quality of life.

Some people diagnosed with Lewy body dementia respond positively to medications called cholinesterase inhibitors. They boost the level of a chemical messenger in the brain called acetylcholine that’s important for memory and other cognitive functions. These drugs may help improve alertness and reduce hallucinations and signs of dementia.

Other medications are available to help decrease the Parkinsonism, hallucinations and other Lewy body dementia symptoms. These medications must be closely monitored by a health care provider. In people who have Lewy body dementia, medications to improve motor function may make symptoms such as hallucinations worse, and medications used to combat dementia may increase Parkinsonism.

Because Lewy body dementia treatment needs to be managed skillfully to obtain the most effective results, people who have this disease should be monitored by a physician with expertise and experience with Lewy body dementia — usually a neurologist or a neuropsychiatrist. — Neill Graff-Radford, M.D., Neurology, Mayo Clinic, Jacksonville, Fla.

(Mayo Clinic Q & A is an educational resource and doesn’t replace regular medical care. E-mail a question to MayoClinicQ&A@mayo.edu. For more information, visit www.mayoclinic.org.)

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