Neurocognitive Disorders — Semantic Variant Frontotemporal Dementia
A 72-year-old woman with type 2 diabetes treated with metformin 1 g twice daily is brought by her family for two years of progressive difficulty naming objects; she calls a cat "an animal" and asks what a "fork" is. Recent memory, orientation, personality and behaviour are preserved. Her brother had a similar illness. Neurological examination is otherwise normal. What is the most likely diagnosis?
- A.Vascular dementia
- B.Alzheimer disease
- C.Frontotemporal dementiaCorrect
- D.Vitamin B12 deficiency with cognitive impairment
Explanation
Progressive anomia combined with loss of word meaning, shown by substituting a general category for a specific name and failing to understand a common noun, while episodic memory, orientation and behaviour remain intact, is the semantic variant of primary progressive aphasia. This is a language presentation of frontotemporal lobar degeneration, caused by anterior temporal lobe atrophy, usually more on the left. The 2011 international consensus criteria require impaired confrontation naming and impaired single-word comprehension as core features, with spared repetition and speech production. Alzheimer disease is the main competitor because word-finding difficulty is common in it, but typical Alzheimer disease begins with loss of recent episodic memory, which is explicitly absent here; its language variant is logopenic, with impaired repetition and preserved word meaning. Vascular dementia follows a stepwise course with focal signs and executive slowing. Long-term metformin can lower vitamin B12, but deficiency causes a global cognitive picture with neuropathy or subacute combined degeneration, not a selective loss of semantic knowledge. A family history supports the frontotemporal spectrum, although the semantic variant is more often sporadic than the behavioural form.
Why each option
- A.
- Vascular dementia shows stepwise decline, focal neurological signs and executive slowing rather than isolated progressive loss of word meaning.
- B.
- Typical Alzheimer disease begins with recent memory loss, and its language variant affects repetition while word meaning is preserved.
- C.
- Correct. Progressive loss of naming and word meaning with preserved memory and behaviour is semantic variant primary progressive aphasia, a frontotemporal dementia.
- D.
- Metformin can lower vitamin B12, but deficiency produces global cognitive slowing with neuropathy, not selective loss of semantic knowledge.
Reference: Gorno-Tempini et al., Classification of primary progressive aphasia and its variants, Neurology 2011; UpToDate — Frontotemporal dementia: clinical features and diagnosis (2025)
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