## Pathological Hallmark of Lewy Body Dementia **Key Point:** Alpha-synuclein is the primary pathological protein in Lewy body dementia (LBD), forming intracytoplasmic inclusions known as Lewy bodies. ### Lewy Bodies: Structure and Composition Lewy bodies are eosinophilic, intracytoplasmic inclusions found predominantly in: - Substantia nigra - Locus coeruleus - Cortical neurons (in cortical Lewy body disease) They are composed of: 1. Alpha-synuclein (core protein) 2. Ubiquitin 3. Neurofilament proteins ### Pathological Protein Comparison in Dementias | Dementia Type | Primary Pathological Protein | Secondary Pathology | |---|---|---| | Lewy Body Dementia | **Alpha-synuclein** | May have tau, amyloid-beta | | Alzheimer's Disease | Amyloid-beta, Tau | Neuritic plaques, tangles | | Frontotemporal Dementia | Tau or TDP-43 | Neuronal loss, spongiosis | | Parkinson's Disease Dementia | Alpha-synuclein | Similar to LBD | **High-Yield:** Alpha-synuclein pathology links Lewy body dementia, Parkinson's disease, and multiple system atrophy — collectively termed "synucleinopathies." **Clinical Pearl:** Lewy bodies can coexist with Alzheimer pathology (amyloid-beta and tau), making mixed pathology common in older adults with dementia. ### Diagnostic Significance The presence of Lewy bodies on neuropathological examination is the gold standard for LBD diagnosis. Immunohistochemistry using anti-alpha-synuclein antibodies confirms the diagnosis at autopsy.
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