A woman in her 70s with type 2 diabetes mellitus on metformin 1 g twice daily has word‑finding difficulty (e.g., calling a cat “animal”) without memory loss or personality change; what is the most likely diagnosis: vascular dementia, Alzheimer disease, frontotemporal dementia, or vitamin B12 deficiency?

Primary Progressive Aphasia (Semantic Variant)

The most likely diagnosis is Primary Progressive Aphasia (PPA), a language-predominant neurodegenerative syndrome that presents with isolated word-finding difficulty and anomia without early memory impairment or personality changes. 1, 2

Clinical Reasoning

This patient's presentation is highly characteristic of PPA based on three key features:

• Isolated language impairment: She demonstrates anomia (word-finding difficulty) with semantic paraphasias (saying "animal" instead of "cat"), which is the hallmark of language network dysfunction 1, 2

• Preserved memory: The explicit absence of memory impairment argues strongly against Alzheimer's disease, which characteristically presents with episodic memory deficits as the predominant early feature 1, 3

• Preserved personality and behavior: The absence of behavioral or personality changes argues strongly against frontotemporal dementia (behavioral variant), which would manifest with prominent personality changes, behavioral disinhibition, loss of empathy, and social cognition deficits as core features 1, 4

Why Other Diagnoses Are Less Likely

Alzheimer's Dementia (Option B)

• Alzheimer's typically presents with episodic memory impairment as the predominant early feature, not isolated language dysfunction 1, 3
• While diabetes increases Alzheimer's risk by 56%, the clinical presentation doesn't match 3, 1
• Diabetes-related cognitive impairment typically presents with more global cognitive decline affecting multiple domains, particularly executive dysfunction 1, 3

Frontotemporal Dementia (Option C)

• The behavioral variant of FTD would require prominent personality changes, behavioral disinhibition, and loss of empathy as core features—all explicitly absent in this case 1, 4
• However, it's important to note that PPA itself is actually a language variant of frontotemporal lobar degeneration 2

Vascular Dementia (Option A)

• Vascular dementia in diabetic patients typically presents with stepwise cognitive decline, executive dysfunction, and often has associated motor findings or clear vascular events 1, 3
• This patient's isolated, progressive language impairment without stepwise decline or motor findings makes vascular dementia unlikely 3

Vitamin B12 Deficiency (Option D)

• While metformin use warrants checking B12 levels (as recommended by the American Diabetes Association), B12 deficiency typically causes more global cognitive and psychiatric disturbances, gait instability, neuropathy, and autonomic dysfunction—not isolated language impairment 3, 5, 6
• B12 deficiency should still be excluded as part of the workup, but the clinical pattern doesn't fit 1, 6

Critical Next Steps

Despite PPA being the most likely diagnosis, vitamin B12 levels must be checked given her metformin use:

• The American Diabetes Association recommends measuring vitamin B12 levels in patients taking metformin 3, 1
• Metformin-associated B12 deficiency is common and can worsen cognitive outcomes 6, 7
• However, B12 deficiency alone would not explain the isolated language presentation 5

Formal neuropsychological evaluation focusing on language domains is recommended to characterize the aphasia pattern and confirm the diagnosis 1, 2

Common Pitfalls to Avoid

• Don't assume all cognitive impairment in diabetic patients is vascular or metabolic: This patient's isolated language presentation is too specific for these diagnoses 1
• Don't overlook PPA because it's less common: The clinical pattern is distinctive and should be recognized early 2
• Don't dismiss the need for B12 testing: Even though it's not the primary diagnosis, metformin-associated B12 deficiency is treatable and may contribute to cognitive decline 3, 6, 7