Clues Pointing TO This Diagnosis

79-year-old woman with about a year of gradual, progressive memory decline — Alzheimer's disease is the most common dementia, most common in women older than 65, with insidious onset over months to years
Repeating the same question several times an hour — impaired retention of recently acquired (short-term/episodic) information is the hallmark early symptom of Alzheimer's disease
Forgetting her own address and getting lost driving on familiar roads — loss of recent episodic memory and topographic orientation reflects the early temporolimbic (hippocampal) involvement typical of Alzheimer's disease
Leaving the stove on twice — inability to reliably complete previously routine, complex daily tasks signals functional decline crossing from normal aging into dementia
Word-finding difficulty ("losing language" she always knew) — impaired language/word retrieval emerges as Alzheimer's disease progresses into the moderate stage
Executive dysfunction on neuropsychological testing — deficits in executive function commonly accompany the amnestic memory impairment of Alzheimer's disease
Preserved long-term/remote memory (singing old songs, humming sonnets) while recent memory fails — memory for remote events is relatively spared until later, a classic Alzheimer's pattern
MRI showing hippocampal atrophy — medial temporal/hippocampal volume loss is the characteristic structural finding supporting Alzheimer's disease
Gradual, steadily progressive course without abrupt stepwise drops — insidious, continuous progression favors a neurodegenerative process over a vascular one
Amnestic presentation overall — roughly 80% of Alzheimer's disease presents with this typical amnestic (hippocampal-type) syndrome

Why It's NOT the Similar Diseases

NOT vascular dementia — Agnes has gradual, continuous progression with isolated hippocampal atrophy, not the stepwise decline, focal neurologic deficits, or infarcts/white matter disease that define vascular dementia
NOT dementia with Lewy body disease — she has no fluctuating alertness, visual hallucinations, REM sleep behavior disorder, or parkinsonism, and her memory (not visuospatial function) is affected first
NOT delirium — her course spans a year with preserved attention and level of consciousness, whereas delirium is acute, fluctuating, and defined by inattention and altered consciousness
NOT frontotemporal dementia — her presentation is amnestic rather than the early personality/behavioral change, disinhibition, or progressive aphasia with relative memory preservation seen in frontotemporal dementia
NOT major depression ("pseudodementia") — she attributed symptoms to stress, but objective neuropsychological deficits plus hippocampal atrophy point to a neurodegenerative process rather than a mood disorder driving the cognitive complaints

Differential Diagnosis List

Vascular dementia — ruled out by gradual (not stepwise) progression, normal neurologic exam, and hippocampal atrophy without infarcts/significant white matter disease
Dementia with Lewy body disease — ruled out by absence of fluctuating cognition, visual hallucinations, and parkinsonism
Delirium — ruled out by the chronic year-long course with preserved attention and consciousness
Frontotemporal dementia — ruled out by the amnestic presentation rather than early behavioral/personality change or aphasia
Reversible causes (e.g., B12 deficiency, hypothyroidism, depression) — ruled out by progressive amnestic decline with hippocampal atrophy, though these should be screened for on workup

Key Distinguishing Test

Alzheimer's dementia is primarily a clinical diagnosis based on the history and neuropsychological testing showing a progressive amnestic (memory-predominant) syndrome. The routine workup adds basic labs (e.g., B12 and TSH) to exclude reversible causes plus structural neuroimaging (MRI or CT); medial temporal/hippocampal atrophy supports Alzheimer's disease and imaging also excludes treatable structural causes. CSF or PET amyloid and tau biomarkers can increase diagnostic certainty when needed.

Board Note

Classic profile: insidious, progressive short-term memory loss in an adult over 65 (more common in women), with a normal early neurologic exam and pathology of beta-amyloid plaques and tau neurofibrillary tangles; life expectancy is roughly 4–8 years after diagnosis
Do the reversible-cause workup: check B12 and TSH and obtain neuroimaging to exclude conditions such as tumor or normal-pressure hydrocephalus before attributing decline solely to Alzheimer's disease
First-line symptomatic pharmacotherapy is a cholinesterase inhibitor (donepezil, rivastigmine, galantamine) for mild-to-moderate disease, adding memantine for moderate-to-severe disease; these slow symptoms modestly but do not reverse the disease
Behavioral and psychological symptoms should be managed first with nonpharmacologic strategies (identifying triggers, structured activities, caregiver support); reserve medications such as brexpiprazole for dangerous refractory agitation, given antipsychotic mortality risk
Prioritize safety and caregiver support: address home hazards (stove safeguards, wandering/driving), and involve caregiver education and respite; discuss goals of care and hospice as the disease reaches advanced stages
Newer anti-amyloid monoclonal antibodies (lecanemab, donanemab) are FDA-approved only for mild cognitive impairment or mild Alzheimer's dementia with confirmed amyloid, slow decline modestly, carry a risk of amyloid-related imaging abnormalities (ARIA), and warrant specialist referral

“Agnes’s Story”