Lewy body dementia (LBD) is an umbrella term for two similar and common subtypes of dementia: dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). Both are characterized by changes in thinking, movement, behavior, and mood. The two conditions have similar features and may have similar causes, and are believed to belong on a spectrum of Lewy body disease that includes Parkinson's disease. As of 2014, they were more often misdiagnosed than any other common dementia. The exact cause is unknown, but involves widespread deposits of abnormal clumps of protein that form in neurons of the diseased brain. Known as Lewy bodies (discovered in 1912 by Frederic Lewy) and Lewy neurites, these clumps affect both the central nervous system and the autonomic nervous system. The fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) gives Lewy body disease as the causative subtype of dementia with Lewy bodies, and Parkinson's disease as the causative subtype of Parkinson's disease dementia. Dementia with Lewy bodies is marked by the presence of Lewy bodies primarily in the cortical regions, and Parkinson's disease dementia with Lewy bodies primarily in the subcortical basal ganglia.
Classification
The synucleinopathies (dementia with Lewy bodies, Parkinson's disease dementia, and Parkinson's disease) are characterized by shared features of parkinsonism motor symptoms, neuropsychiatric symptoms, impaired cognition, sleep disorders, and visual hallucinations. The Lewy body dementias—dementia with Lewy bodies (DLB), and Parkinson's disease dementia (PDD)—are distinguished by the timing when cognitive and motor symptoms appear. The two Lewy body dementias are often considered to belong on a spectrum of Lewy body disease that includes Parkinson's disease. MeSH lists Lewy body disease in several categories: as a nervous system disease in two listings, one as a basal ganglia Parkinsonian movement disorder and the other under brain disease as a dementia; as a neurodegenerative disorder listed as a synucleinopathy; and as a neurocognitive disorder listed with dementia. A genetic architecture that predisposes an individual to some disease phenotypes is found in Parkinson's disease and the Lewy body dementias. The presence of Lewy bodies is a link between these disorders; the term "diseases with Lewy bodies" therefore may be more accurate than "Lewy body disease".
Cause and mechanisms
Dementia with Lewy bodies and Parkinson's disease dementia are similar in many ways, suggesting there may be a common pathophysiological mechanism, with PDD and DLB at opposite ends of a Lewy body disease spectrum, and a shared component of protein deposits in Lewy bodies and Lewy neurites. Lewy bodies and neurites have been found to develop from the aggregation of misfolded alpha-synuclein, a protein thought to assist in neurotransmitter release and vesicle turnover; whether these misfolded proteins are responsible for the neurodegenerative effects remains unclear, and no definitive link between Lewy bodies and neurodegenerative effects has been found. DSM-5 gives Lewy body disease as the causative subtype of DLB, and Parkinson's disease as the causative subtype of PDD. DLB is marked by the presence of Lewy bodies primarily in the cortical regions, and PDD with Lewy bodies primarily in the subcortical basal ganglia. Despite differences in the timing of the appearance of symptoms, the two dementias "show remarkably convergent neuropathological changes at autopsy". The relationship between Parkinson's disease dementia and dementia with Lewy bodies is unclear as of 2020, but there is likely to be genetic overlap, and the two conditions may represent different points on a continuum.
Diagnosis
Dementia with Lewy bodies and Parkinson's disease dementia have similar neuropathological features, but these features are highly variable and the conditions cannot be distinguished on pathological features alone. Generally, dementia with Lewy bodies is distinguished from Parkinson's disease dementia by the time frame in which dementia symptoms appear relative to parkinsonian symptoms and is diagnosed when cognitive symptoms begin before or at the same time as parkinsonism. Parkinson's disease dementia is the diagnosis when Parkinson's disease is already well established before the dementia occurs.
Epidemiology
Between 5% and 25% of diagnosed dementias in older adults are due to one of the Lewy body dementias. As of 2014, the Lewy body dementias affect about 1.3 million people in the US and 140,000 in the UK. LBD usually develops after the age of 50. Men are slightly more likely to be diagnosed than women.
Prognosis
Life expectancy of people with one of the LBD is reduced; following diagnosis it ranges on average from five to eight years.
Society and culture
Advocacy and awareness As of 2014, the Lewy body dementias were more often misdiagnosed than any other common dementia. Most people with DLB had not heard of the condition prior to diagnosis; general awareness about LBD lags well behind that of Parkinson's and Alzheimer's diseases, even though LBD is the second most common dementia, after Alzheimer's. It is not only frustrating for families and caregivers to find that few people, including many healthcare professionals, are knowledgeable about LBD; lack of knowledge can have significant health consequences because people with LBD have severe sensitivity to antipsychotics often used to treat the symptoms. The Lewy Body Dementia Association (LBDA) and the UK Lewy Body Society promote awareness and provide support that helps society, by reducing costly use of healthcare, and families with LBD, by reducing stress. These organizations, and others in Argentina, Australia and Japan, help raise knowledge and help families with LBD become advocates to raise awareness about the disease.
Notable individuals
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