Lewy Body Dementia

Overview

Lewy body dementia (LBD) is an umbrella term encompassing two subtypes of dementia: dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD). Both subtypes are characterised by alterations in cognition, movement, behaviour, and mood. These conditions are part of a spectrum of Lewy body disease that also includes Parkinson's disease. As of 2014, LBD was the most commonly misdiagnosed form of dementia.

The exact cause of LBD is unknown but involves widespread deposits of abnormal protein clumps, known as Lewy bodies and Lewy neurites, in the neurons of the brain. These deposits affect both the central and autonomic nervous systems.

The fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) identifies 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.

Lewy bodies primarily affect the cortical regions in DLB and the subcortical basal ganglia in PDD.

Classification

LBD is part of the synucleinopathies group, which also includes Parkinson's disease. These conditions share features such as parkinsonian motor symptoms, neuropsychiatric symptoms, impaired cognition, sleep disorders, and visual hallucinations. The distinction between DLB and PDD lies in the timing of cognitive and motor symptom onset.

Generally, DLB is diagnosed when cognitive symptoms appear before or simultaneously with parkinsonism, while PDD is diagnosed when Parkinson's disease is well established before the onset of dementia.

MeSH categorises Lewy body disease under several listings, including as a nervous system disease, a neurodegenerative disorder, and a neurocognitive disorder.

Cause and Mechanisms

DLB and PDD are thought to share a common pathophysiological mechanism, with both conditions lying at opposite ends of a Lewy body disease spectrum. The shared component is the presence of protein deposits in Lewy bodies and Lewy neurites, which develop from the aggregation of misfolded alpha-synuclein.

Although these misfolded proteins are implicated in neurotransmitter release and vesicle turnover, their direct neurodegenerative effects remain unclear. Despite differences in symptom onset timing, DLB and PDD show similar neuropathological changes at autopsy, suggesting genetic overlap and a continuum between the two conditions.

Diagnosis

DLB and PDD have similar neuropathological features but differ in the timing of symptom appearance. DLB is diagnosed when cognitive symptoms begin before or at the same time as parkinsonism, while PDD is diagnosed when dementia occurs after Parkinson's disease is well established.

Epidemiology

LBD accounts for 5% to 25% of diagnosed dementias in older adults. As of 2014, approximately 1.3 million people in the US and 140,000 in the UK were affected by LBD. The condition usually develops after the age of 50, with men being more likely to be diagnosed than women.

Prognosis

The life expectancy of individuals with LBD is reduced, with an average range of five to eight years following diagnosis.

Society and Culture

Advocacy and Awareness

As of 2014, LBD was the most commonly misdiagnosed form of dementia. General awareness of LBD lags behind that of Parkinson's and Alzheimer's diseases, despite LBD being the second most common dementia after Alzheimer's.

Misdiagnosis can have significant health consequences, as individuals with LBD have severe sensitivity to antipsychotics. Organisations such as the Lewy Body Dementia Association (LBDA) and the UK Lewy Body Society promote awareness and provide support, helping reduce healthcare costs and stress for families.

Notable Individuals

Robin Williams (shown in 2011): his widow said he was diagnosed on autopsy with Lewy bodies.

Robin Williams, the American actor and comedian, experienced symptoms of depression, anxiety, and paranoia before his suicide in 2014. An autopsy revealed diffuse Lewy body disease, a condition more commonly referred to as diffuse Lewy body dementia. This terminology highlights the underlying pathological process of Lewy bodies spread throughout the brain.

Self-assessment MCQs (single best answer)

What are the two subtypes of Lewy Body Dementia (LBD)?

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What protein is primarily involved in the formation of Lewy bodies and Lewy neurites?

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Which of the following is a key difference between DLB and PDD?

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What is the estimated percentage of diagnosed dementias in older adults that LBD accounts for?

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Which organisation is dedicated to promoting awareness and providing support for those affected by LBD in the US?

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What is the average life expectancy following a diagnosis of LBD?

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Which notable individual was diagnosed with diffuse Lewy body disease on autopsy?

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Which of the following symptoms is commonly seen in individuals with LBD?

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What does the fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) identify as the causative subtype of dementia with Lewy bodies?

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In what year was LBD reported to be the most commonly misdiagnosed form of dementia?

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