Alzheimer Disease vs Vascular Dementia

Why Lecanemab is correct

• The picture is early Alzheimer disease (AD): amnestic decline with an MMSE of 23/30 (mild dementia range) plus a confirmatory CSF biomarker profile of low Abeta42 and elevated total-tau and phospho-tau
• Lecanemab is an anti-amyloid-beta monoclonal antibody directed at soluble protofibrils and is FDA-approved for mild cognitive impairment or mild dementia due to AD with confirmed amyloid pathology
• In the CLARITY-AD trial it slowed clinical decline by roughly 27% versus placebo over 18 months, making it disease-modifying rather than purely symptomatic
• Eligibility requires confirmed amyloid pathology (CSF or amyloid PET) and a baseline MRI; donanemab is a similarly disease-modifying alternative

Why the others are wrong

• Donepezil — a cholinesterase inhibitor that improves symptoms by raising synaptic acetylcholine but does not alter amyloid pathology or the disease trajectory (right-concept-wrong-mechanism)
• Solanezumab — also an anti-amyloid monoclonal antibody, but it binds monomeric soluble Abeta rather than the protofibrils and deposited plaque that have to be cleared; it failed to slow decline in the EXPEDITION program and in the A4 trial and was never approved, so it does not modify the disease (right-class-wrong-target)
• Memantine — an NMDA-receptor antagonist used in moderate-to-severe AD for symptom control, not to slow underlying pathology (anchoring on AD label without matching mechanism)

Additional high-yield points

• Amyloid-related imaging abnormalities (ARIA-E edema, ARIA-H microhemorrhage) require serial MRI monitoring during anti-amyloid therapy
• APOE4 carriers (especially homozygotes) have higher ARIA risk, and concurrent anticoagulation raises ARIA-H/hemorrhage risk, so genotype and bleeding risk should be assessed before starting

Why Small-vessel ischemia disrupting frontosubcortical circuits is correct

• The picture is subcortical ischemic vascular dementia (Binswanger-type): vascular risk factors, stepwise decline, early gait disturbance, executive dysfunction, and pyramidal/pseudobulbar signs.
• MRI lacunes in the basal ganglia plus confluent white matter hyperintensities (leukoaraiosis) interrupt the frontal-subcortical loops, producing slowed processing and executive impairment with relatively preserved, cueable memory.
• Per NINDS-AIREN/VASCOG criteria, cognitive decline plus cerebrovascular disease on imaging with a temporal/causal link establishes vascular dementia; aggressive vascular risk-factor control is the mainstay of management (intensive BP control reduced incident mild cognitive impairment in SPRINT-MIND, a prevention trial in adults without dementia).

Why the others are wrong

• Extracellular beta-amyloid plaques and neurofibrillary tangles — the mechanism of Alzheimer disease, which causes insidious, memory-predominant decline with medial temporal atrophy, not lacunes/leukoaraiosis with early gait failure.
• Intraneuronal alpha-synuclein (Lewy body) aggregate deposition — underlies dementia with Lewy bodies, expected to show fluctuating cognition, visual hallucinations, parkinsonism, and REM sleep behavior disorder, none of which are present.
• Impaired cerebrospinal fluid resorption with ventriculomegaly — the mechanism of normal pressure hydrocephalus; its triad includes magnetic gait and incontinence, but imaging shows ventriculomegaly out of proportion to atrophy rather than multiple lacunar infarcts and confluent white matter ischemia.