Q-Bank Breakdown: Frontotemporal dementia — Why Every Answer Choice Matters

Frontotemporal dementia (FTD) is a classic “USMLE trap” diagnosis because the patient can look psychiatric, the MRI can look deceptively normal early on, and the distractors often include Alzheimer disease (AD) and dementia with Lewy bodies (DLB)—which are much more familiar. The way to win these questions is to anchor yourself to what changes first (behavior/language vs memory), then use age, focal findings, and hallmark clues to demolish every answer choice.

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Clinical Vignette (Q-bank style)

A 58-year-old man is brought by his spouse for progressive personality changes over 2 years. He has become socially inappropriate, makes rude jokes, and has started compulsively eating sweets and snacking throughout the day. He was recently fired for violating workplace norms. He forgets appointments occasionally, but he can recall recent events when prompted. Neurologic exam is normal. Mini-Cog is mildly abnormal but he is oriented. MRI shows frontal and anterior temporal lobe atrophy, greater on the right.

Most likely diagnosis?

A. Alzheimer disease
B. Dementia with Lewy bodies
C. Frontotemporal dementia
D. Huntington disease
E. Normal pressure hydrocephalus

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Correct Answer: C. Frontotemporal Dementia

Why FTD fits best

FTD is defined by early behavioral disinhibition or primary progressive aphasia, typically with earlier onset than AD.

High-yield clues in this vignette

• Age < 65 (often 45–65): strongly favors FTD over typical AD
• Early personality/behavior change: disinhibition, loss of empathy, apathy, compulsions
• Hyperorality: compulsive eating, sweet cravings
• Memory relatively preserved early: may have “forgetfulness,” but it’s not the primary deficit at first
• Imaging: frontal and anterior temporal atrophy (often “knife-edge” atrophy on gross pathology)

Core clinical patterns to recognize

FTD commonly presents as:

• Behavioral variant FTD (bvFTD): disinhibition, apathy, compulsions, dietary changes
• Primary progressive aphasia (PPA)
  • Nonfluent/agrammatic: effortful speech
  • Semantic variant: loss of word meaning (impaired naming/comprehension)

Pathology associations (Step-relevant)

FTD is a clinical syndrome with several pathologies underneath it, commonly:

• Tauopathies (Pick disease → Pick bodies)
• TDP-43 inclusions (also associated with some ALS cases)

Pearl: FTD and ALS can overlap clinically and pathologically (TDP-43).

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How to Systematically Eliminate the Distractors

A. Alzheimer Disease

Why it’s tempting: “Dementia” + mild forgetfulness.

Why it’s wrong here

• AD typically starts with episodic memory impairment (hippocampal dysfunction): repeating questions, getting lost, poor new learning
• Behavioral disinhibition can happen, but usually later
• Typical onset is > 65 (though early-onset exists, the vignette is built around classic FTD features)

What you’d expect instead

• Early: short-term memory loss > personality change
• Imaging: medial temporal lobe/hippocampal atrophy
• Path: $\beta$-amyloid plaques + tau neurofibrillary tangles

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B. Dementia with Lewy Bodies

Why it’s tempting: Another common dementia diagnosis with “non-memory” symptoms.

Why it’s wrong here DLB is defined by:

• Visual hallucinations
• Fluctuating cognition/attention
• Parkinsonism (bradykinesia, rigidity)
• REM sleep behavior disorder (often a major clue)

This patient has none of those—his key issue is behavioral disinhibition + hyperorality.

High-yield add-on: DLB patients are often very sensitive to typical antipsychotics (can worsen parkinsonism, precipitate severe reactions).

What you’d expect instead

• Early hallucinations + parkinsonism + fluctuations
• Path: $\alpha$-synuclein Lewy bodies in cortex

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D. Huntington Disease

Why it’s tempting: Behavioral changes can occur and it’s a neurodegenerative disease.

Why it’s wrong here

• Huntington is characterized by chorea, dystonia, and motor abnormalities—often prominent on exam
• Strong autosomal dominant family history is common
• Usually presents with a triad: movement disorder + psychiatric symptoms + cognitive decline

This patient’s neuro exam is normal and the vignette gives focal frontotemporal atrophy, not caudate findings.

What you’d expect instead

• Chorea, saccadic pursuit abnormalities
• Imaging: caudate atrophy with enlarged frontal horns
• Genetics: CAG repeat expansion with anticipation (classically paternal)

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E. Normal Pressure Hydrocephalus (NPH)

Why it’s tempting: Dementia is in the classic triad.

Why it’s wrong here NPH is the “wet, wobbly, wacky” triad:

• Gait disturbance (usually earliest and most prominent)
• Urinary incontinence
• Cognitive impairment (often subcortical/frontal “slowness”)

This vignette lacks gait dysfunction and urinary symptoms, and MRI is described as frontotemporal atrophy, not ventriculomegaly out of proportion to cortical atrophy.

What you’d expect instead

• Magnetic gait, falls, urinary urgency/incontinence
• Imaging: ventriculomegaly with relatively preserved sulci
• Large-volume LP may transiently improve symptoms

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Rapid Comparison Table (Test-day Fast Thinking)

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USMLE High-Yield Takeaways (What They Love to Ask)

• FTD = early behavior or language changes with relative memory preservation early
• Younger onset (<65) strongly supports FTD
• Hyperorality (sweet cravings, binge eating) is a classic clue
• DLB = visual hallucinations + fluctuations + parkinsonism + REM sleep behavior disorder
• NPH: gait first, then urinary, then cognitive; ventriculomegaly
• When stuck, ask: “What is the first and most prominent deficit?”
  • Memory first → AD
  • Behavior/language first → FTD
  • Hallucinations/fluctuations/parkinsonism → DLB
  • Gait + incontinence → NPH
  • Chorea + psych + AD inheritance → Huntington