A form of dementia, the symptoms of which resemble those of Alzheimer’s disease, that results from lewy body infiltration of brain tissue and in which there are components of motor function impairment similar to the symptoms of Parkinson’s disease. The condition is sometimes called diffuse Lewy body disease. It generally affects people who are older than age 60, although it can occur in people who are younger. The blend of symptoms makes differentiation of Lewy body disease from Parkinson’s disease and Alzheimer’s disease difficult.
Pathology and Symptoms of Lewy Body Disease
Lewy body disease resembles a combination of Alzheimer’s and Parkinson’s, as the person shows some of the classic or hallmark symptoms of each disease but full symptoms for neither disease. As well, Lewy body disease has a faster progression than either Alzheimer’s or Parkinson’s alone; typically death occurs within 10 to 15 years of the onset of symptoms. Neurologists have established the following diagnostic criteria for Lewy body disease:
• Significant and progressive cognitive impairment including two or more symptoms such as memory loss, thought disturbances, loss of analytical reasoning skills, delusions, and dementia
• Distinctive fluctuations in mental alertness and ability to focus, as the person experiences alternating periods of lucidity and impairment
• Persistent visual hallucinations (seeing of objects or people that are not present)
• Frequent, unexplained falls or evidence of extrapyramidal symptoms such as the neuro-muscular symptoms characteristic of Parkinson’s disease
• Unexplained fainting or brief episodes of loss of consciousness
The overlaps with Parkinson’s disease and Alzheimer’s disease are obvious and make diagnosis difficult. Although at present this distinction makes little difference in the course of any of these diseases, it may in the near future provide further insights into the mechanisms of, and relationships among, all three that lead to more effective treatments.
Treatment of Lewy Body Disease
Treatment, as does diagnosis, remains an area of uncertainty. Medications to treat the symptoms of Alzheimer’s disease generally are not effective at relieving dementia or improving cognitive function in Lewy body disease. anti-parkinson’s medications can relieve motor symptoms in those who have them, although the dementia continues to progress.
Doctors commonly prescribe atypical antipsychotic medications (especially quetiapine) for people with moderate to severe Alzheimer’s disease, to relieve dementia symptoms. Although doctors know that some people with Alzheimer’s experience dystonia (muscles “frozen” in distorted and often painful positions) and other serious motor symptoms as undesired side effects of antipsychotic medications, the reason for the apparent randomness of their incidence has eluded understanding. Researchers know, however, that the presence of Lewy bodies in the cerebrum, where they affect cognitive functions, increases the likelihood that they are present throughout the brain including the basal ganglia, where they affect motor functions. At the least, the diffusion of Lewy bodies into regions of the brain involved with movement compromises the functions of the extrapyramidal system (the network of nerve structures that serves as the viaduct for nerve-muscle communication).
Scientists speculate that little is required to push that compromise into dysfunction, causing motor symptoms to surface. In similar fashion, anti-Parkinson’s medications often relieve motor symptoms in people with Lewy body disease but cause the emergence of symptoms of psychosis, for which the treatment of choice would ordinarily be an antipsychotic medication but in Lewy body disease is likely to exacerbate motor symptoms. Attempts to find the appropriate balance of medications to treat all of the symptoms becomes a spiral of frustration as one solution leads to other problems.
One bright spot in treatment is that many people who have symptoms of both Parkinson’s and Alzheimer’s, but may actually have Lewy body disease, is that symptoms of both diseases respond particularly well to ACETYLCHOLINESTERASE INHIBITOR medications such as rivastigmine (Exelon), DONEPEZIL (Aricept), galantamine (Reminyl), and tacrine (Cognex); these are all called cholinesterase inhibitors, which extend the activity of acetyl-choline in the brain. Acetylcholine is a neurotrans-mitter with key functions in cognition that becomes depleted in Alzheimer’s disease; scientists believe that its depletion is the core cause of the symptoms of Alzheimer’s (as dopamine depletion is similarly the core cause of the symptoms of Parkinson’s). Doctors typically prescribe acetylcholinesterase inhibitors to improve cognitive function and in doing so for people with Parkinson’s who are experiencing cognitive impairment have discovered that these drugs also may improve motor symptoms in some people. Much research remains necessary to explore this effect, however, and at present the U.S. Food and Drug Administration (FDA) has approved acetylcholinesterase inhibitors only to treat cognitive dysfunction in Alzheimer’s disease.
Why Lewy Body Disease Interests Parkinson’s Disease Researchers Parkinson’s disease and Alzheimer’s disease are far likelier to coexist with each other than chance would dictate. When they do, brain autopsy shows tau plaques (protein-based deposits that lack the specific structure of Lewy bodies) and neurofibrillary entanglements with Alzheimer’s disease as well as Lewy body deposits. This overlapping of symptoms and possibly of disease processes not only is part of the reason diagnosis and treatment are so challenging for these symptoms, but also is causing scientists to reconsider the disease definitions. Some researchers believe that people who have symptoms of both Alzheimer’s and Parkinson’s instead have Lewy body disease.
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