Distinguishing Dementia, Alzheimer's Disease, and Lewy Body Dementia

Introduction to Dementia

Dementia is a clinical syndrome, not a specific disease, describing cognitive or behavioral symptoms that interfere with daily function, regardless of the underlying cause, affecting patients with various underlying pathologies 1
Multiple diseases can cause dementia, including Alzheimer's disease, Lewy body dementia, vascular disease, frontotemporal dementia, and others, with most patients over 80 having mixed etiology dementia 1

Alzheimer's disease is characterized by amyloid plaques and neurofibrillary tangles in the brain, typically presenting with prominent memory loss as the earliest and most severe symptom, according to the American Academy of Neurology 2, 3
Pure Alzheimer's disease pathology is found in only 3-30% of dementia cases at autopsy, depending on age, with 50-60% of clinically diagnosed Alzheimer's dementia having contributing copathologies, as stated by the American Geriatrics Society 2, 3, 6

Lewy body dementia is characterized by abnormal deposits of alpha-synuclein protein forming Lewy bodies in the brain, presenting with a distinctive triad of fluctuating cognition, visual hallucinations, and parkinsonism, as outlined by the National Institute on Aging 5, 7
The presence of core features such as fluctuating cognition, visual hallucinations, parkinsonism, or RBD indicates LBD as the primary diagnosis, even if amyloid biomarkers are positive, according to the American Academy of Neurology 5, 4

The clinical phenotype trumps biomarkers in diagnosing LBD, with the diagnosis relying on the presence of core clinical features rather than biomarker results alone, as recommended by the International Society for Frontotemporal Dementia 5
If any LBD "red flags" are present, LBD is the primary diagnosis, and traditional antipsychotics must be avoided due to severe neuroleptic sensitivity, as warned by the American Psychiatric Association 5

For Alzheimer's disease, cholinesterase inhibitors and memantine are standard treatments, with antipsychotics used cautiously if needed for behavioral symptoms, as suggested by the American College of Physicians 1
For Lewy body dementia, cholinesterase inhibitors are first-line treatment for both cognitive symptoms and visual hallucinations, with traditional antipsychotics contraindicated due to life-threatening neuroleptic sensitivity, as stated by the National Institute of Mental Health 5

When evaluating any patient with dementia, actively screen for LBD features before defaulting to an Alzheimer's diagnosis to avoid dangerous medication errors and worse outcomes, as advised by the American Medical Association 5, 4