Q-Bank Breakdown: Alzheimer disease — Why Every Answer Choice Matters

You know the feeling: you read a Q-bank vignette, pick “Alzheimer disease,” get it right… and move on. But Step 1/2 writers are banking on you not mastering the distractors. The fastest way to climb from “recognize it” to “own it” is to force every answer choice to teach you something.

Tag: Neurology > Neurodegenerative & Demyelinating

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The Vignette (Q-bank style)

A 72-year-old woman is brought by her daughter for progressively worsening memory problems over 3 years. She frequently misplaces items, repeats questions, and recently got lost driving home from a familiar grocery store. She has difficulty managing finances and needs help with medications. There are no hallucinations. Exam shows impaired short-term recall and difficulty with visuospatial tasks (clock-drawing). Gait is normal. MRI shows diffuse cortical atrophy, most prominent in the medial temporal lobes.

Which of the following is the most likely underlying pathologic finding?

A. Intracytoplasmic inclusions composed of $\alpha$-synuclein in brainstem nuclei
B. Extracellular $\beta$-amyloid plaques and intraneuronal neurofibrillary tangles
C. Demyelination with periventricular plaques and oligoclonal bands in CSF
D. Spongiform change with PrP deposition and periodic sharp wave complexes on EEG
E. Enlarged ventricles with normal CSF pressure and gait apraxia

Correct answer: B. Extracellular $\beta$-amyloid plaques and intraneuronal neurofibrillary tangles

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Why B is Correct (Alzheimer disease core)

Clinical pattern that screams Alzheimer

• Insidious onset + gradual progression over years
• Early episodic memory impairment (hippocampal/medial temporal lobe involvement)
• Loss of independent function (finances, meds, getting lost) = major neurocognitive disorder
• No early hallucinations (points away from Lewy body)
• Normal gait early (points away from normal pressure hydrocephalus)

What you’re expected to know pathologically

Alzheimer disease (AD) has two headline lesions:

Biochem/genetics quick hits (USMLE favorites)

• APP processing: cleavage by $\beta$-secretase and $\gamma$-secretase $\rightarrow A\beta$ accumulation
• Presenilin 1/2 mutations (components of $\gamma$-secretase) $\rightarrow$ early-onset AD
• Down syndrome (trisomy 21): extra APP gene $\rightarrow$ early amyloid deposition (often symptomatic by middle age)
• ApoE4: increased risk and earlier onset (late-onset AD association)

Imaging correlation

• Medial temporal lobe/hippocampal atrophy is classic (fits the vignette).

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Make Every Distractor Pay Rent

A. Intracytoplasmic inclusions composed of $\alpha$-synuclein in brainstem nuclei

What this actually describes: Parkinson disease / Lewy body spectrum

Clue words for $\alpha$-synuclein:

• Lewy bodies (eosinophilic cytoplasmic inclusions) = $\alpha$-synuclein
• Parkinson: bradykinesia, rigidity, resting tremor, postural instability
• Dementia with Lewy bodies (DLB): dementia + visual hallucinations + fluctuating cognition + parkinsonism

Why it’s wrong here:

• No parkinsonism
• No visual hallucinations
• Course is classic slow AD-type decline (DLB often has prominent hallucinations and fluctuations early)

Test-day pearl:
If the stem emphasizes visual hallucinations early, think Lewy body dementia before you think AD.

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C. Demyelination with periventricular plaques and oligoclonal bands in CSF

What this actually describes: Multiple sclerosis (MS)

Clue words for MS:

• Young adult (often woman), relapsing-remitting neurologic deficits
• Optic neuritis (painful monocular vision loss)
• Internuclear ophthalmoplegia
• MRI: periventricular plaques (“Dawson fingers”)
• CSF: oligoclonal IgG bands, increased IgG index

Why it’s wrong here:

• Age 72 + progressive memory/cognition symptoms without focal neuro deficits is not MS
• MS is inflammatory demyelination; this vignette is cortical neurodegeneration

Board-style pitfall:
MS causes cognitive issues sometimes, but it won’t look like isolated, steadily progressive hippocampal amnesia in an elderly patient.

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D. Spongiform change with PrP deposition and periodic sharp wave complexes on EEG

What this actually describes: Creutzfeldt-Jakob disease (CJD)

Clue words for CJD:

• Rapidly progressive dementia (weeks to months, not years)
• Myoclonus
• Ataxia, behavioral changes
• EEG: periodic sharp wave complexes
• Path: spongiform encephalopathy from prion protein misfolding

Why it’s wrong here:

• This patient’s decline is over 3 years, classic for AD
• No myoclonus, no rapidly progressive course

Memory hook:
AD is a slow burn. CJD is a medical emergency masquerading as dementia.

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E. Enlarged ventricles with normal CSF pressure and gait apraxia

What this actually describes: Normal pressure hydrocephalus (NPH)

Clue words for NPH:

• Triad: Wet, Wobbly, Wacky
  • Urinary incontinence
  • Gait disturbance (magnetic gait/gait apraxia) — often earliest and most prominent
  • Cognitive impairment (subcortical/frontal “slowness”)
• Imaging: ventriculomegaly out of proportion to cortical atrophy
• Treatment: high-volume lumbar puncture (tap test) and/or shunt

Why it’s wrong here:

• Her gait is normal
• Symptoms start with episodic memory + visuospatial impairment (more cortical/hippocampal), not the classic gait-first NPH picture

Step 2 pearl:
If gait is the headline and ventricles are big, you’re meant to think NPH because it’s potentially reversible.

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High-Yield Alzheimer Disease: What Q-banks Love to Ask

1) Earliest deficits (and where)

• Early AD: episodic memory (hippocampus/entorhinal cortex)
• As it progresses: language (aphasia), visuospatial dysfunction, executive dysfunction

2) Neurotransmitter angle (Step 1 classic)

• Loss of cholinergic neurons in the basal forebrain (nucleus basalis of Meynert)
• Drugs that target symptoms:
  • Acetylcholinesterase inhibitors: donepezil, rivastigmine, galantamine
  • NMDA antagonist: memantine (moderate-severe)

3) Path buzzwords that should trigger AD instantly

• Neuritic plaques = $A\beta$ extracellular
• Neurofibrillary tangles = tau intraneuronal
• Cerebral amyloid angiopathy (amyloid in vessel walls) $\rightarrow$ lobar hemorrhages (especially in elderly)

4) Differentiating AD from other common dementias (rapid table)

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How to “Break Down” the Next Dementia Question (Fast)

When you see an older adult with cognitive decline, force yourself to answer three questions:

1. Time course: years (AD/DLB) vs weeks–months (CJD) vs stepwise (vascular)
2. First and loudest symptom: memory (AD) vs hallucinations/fluctuations (DLB) vs gait/incontinence (NPH) vs behavior/language (FTD)
3. One pathology anchor:
   • AD: $A\beta$ plaques + tau tangles
   • DLB/Parkinson: $\alpha$-synuclein
   • CJD: prion spongiform
   • MS: periventricular demyelination + oligoclonal bands
   • NPH: ventriculomegaly + gait apraxia

If you can do that, the distractors stop being traps and start being free points.