The Difference Between Lewy Body Dementia, Parkinson’s Disease and Alzheimer’s Disease

Lewy Body Dementia

Lewy Body Dementia: A Common Yet Underdiagnosed Dementia

While it’s not a household word yet, Lewy body dementia (LBD) is not a rare disease. It affects an estimated 1.4 million individuals and their families in the United States. Because LBD symptoms can closely resemble other more commonly known disorders like Alzheimer’s disease and Parkinson’s, it is often underdiagnosed or misdiagnosed. In fact, many doctors or other medical professionals still are not familiar with LBD.

What is Lewy Body Dementia?

Lewy body dementia is not a single disorder but rather a spectrum of closely-related disorders involving disturbances of cognition, behavior, sleep, movement and autonomic function.

In these progressive disorders, Lewy bodies (abnormal deposits of a protein called alpha-synuclein) build up in the brain. Lewy bodies in the brain stem cause a disruption in the production of chemical messengers (neurotransmitters) called dopamine. Too little dopamine can cause parkinsonism, a clinical syndrome that’s characterized by tremor, bradykinesia (slow movement), rigidity and postural instability. Parkinsonism can be caused by Parkinson’s disease itself as well as by other underlying neurological conditions such as LBD.  These Lewy bodies are also found throughout other areas of the brain, including the cerebral cortex. The neurotransmitter acetylcholine is also depleted, causing disruption of perception, thinking and behavior.

A German neurologist, Friederich H. Lewy, first discovered the abnormal protein deposits (later named Lewy bodies) in the early 1900s as he was conducting research on Parkinson’s disease.

What’s the Difference Between Lewy Body Dementia, Parkinson’s Disease and Alzheimer’s Disease?

Lewy body dementia is an umbrella term for two related clinical diagnoses: “dementia with Lewy bodies” and “Parkinson’s disease dementia.” These disorders share the same underlying changes in the brain and very similar symptoms, but the symptoms appear in a different order depending on where the Lewy bodies first form.

Dementia with Lewy bodies (DLB) is a type of dementia that causes problems with memory and thinking abilities that are severe enough to interfere with everyday activities. It specifically affects a person’s ability to plan and solve problems, called executive function, and their ability to understand visual information. Dementia always appears first (or around the same time as parkinsonism) in DLB. The motor symptoms of Parkinson’s such as tremor, slowness, stiffness and walking/balance/gait problems usually become more evident as the disease progresses. Visual hallucinations, REM sleep behavior disorder, fluctuating levels of alertness and attention, mood changes and autonomic dysfunction are also characteristic of DLB.

In contrast, Parkinson’s disease dementia (PDD) is a term used for dementia that develops after several or many years of living with Parkinson’s, a disease that is caused by loss of dopamine-producing nerve cells. In nearly all cases of Parkinson’s, people experience motor symptoms in the early stages; some may also have very mild changes in cognition at diagnosis. Over time, non-motor symptoms of Parkinson’s may appear, including cognitive impairment, REM sleep disorder, memory problems, fatigue, anxiety, autonomic dysfunction, pain and more. Most importantly, not all people with Parkinson’s will develop dementia and at this time, it’s impossible to predict which individuals with Parkinson’s will also develop Parkinson’s disease dementia.

Finally, Alzheimer’s is characterized by different abnormal clumps called amyloid plaques, and jumbled fiber bundles called tau tangles. These microscopic structural changes in the brain were discovered by Dr. Alois Alzheimer in 1906. These plaques and tangles, together with loss of connections between nerve cells, contribute to loss of coherence and memory, as well as a progressive impairment in conducting normal activities of daily living.

Alzheimer’s disease is associated with a lack of acetylcholine, a neurotransmitter in both the peripheral nervous system (PNS) and central nervous system (CNS). Damage initially occurs in the hippocampus, a part of the brain that is involved in memory formation. Other portions of the brain, such as the temporal, parietal and frontal cortices, are progressively affected in those with Alzheimer’s disease.

In comparison, people with dementia with Lewy bodies (DLB) may first present with REM sleep behavior disorder years or even decades before developing dementia, or they may experience visual hallucinations early in the course of their dementia. These are features that help differentiate DLB from Alzheimer’s, even in the early stage of dementia.

Download this free brochure from the Lewy Body Dementia Association to see a comparison chart of the symptoms of LBD, Parkinson’s and Alzheimer’s disease.

What Causes Lewy Body Dementia?

The causes of LBD are not yet well understood, but research is ongoing in this area. There are probably multiple factors involved, including genetic and environmental risk factors that combine with natural aging processes to make someone susceptible to LBD.

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Modified with permission from the Lewy Body Dementia Association

To learn more about motor symptoms related to Parkinson’s, visit here.

To learn more about non-motor symptoms related to Parkinson’s, visit here.

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