What is the most likely diagnosis for a patient in their late 70s with type 2 diabetes mellitus (DM) on metformin (generic name: metformin hydrochloride) 1g twice daily, who has difficulty naming objects, such as saying 'animal' instead of 'cat', without memory impairment or personality changes?

Primary Progressive Aphasia (Semantic Variant)

The most likely diagnosis is Primary Progressive Aphasia (PPA), specifically the semantic variant, which presents with isolated progressive language impairment—particularly anomia (difficulty naming objects)—without early memory loss or personality changes. 1, 2

Why Primary Progressive Aphasia is Most Likely

Clinical Features That Match PPA

• Isolated anomia without memory impairment: The patient demonstrates word-finding difficulties (saying "animal" instead of "cat") while episodic memory for recent events remains preserved, which is the hallmark presentation of PPA 1, 2

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

• Progressive language dysfunction: PPA is diagnosed when language impairment arises in relative isolation and is progressive in nature, reflecting selective atrophy of the language network 2

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
• While diabetes increases Alzheimer's risk by 56%, the clinical presentation here does not match the typical Alzheimer's pattern 3, 1
• Diabetes-related cognitive impairment typically presents with more global cognitive decline affecting multiple domains, particularly executive dysfunction, rather than isolated anomia 1, 4

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
• The gradual, progressive language-specific impairment without stepwise decline or vascular events makes this diagnosis unlikely 1
• While diabetes increases vascular dementia risk by 127%, the clinical pattern doesn't fit 3

Frontotemporal Dementia (Option C)

• The absence of behavioral or personality changes argues strongly against frontotemporal dementia 1
• Behavioral variant FTD would require prominent personality changes, behavioral disinhibition, and loss of empathy as core features, which are explicitly absent in this case 1

B12 Deficiency (Option D)

• While metformin can reduce B12 levels and checking B12 is recommended in patients taking metformin, B12 deficiency typically does not present with isolated progressive anomia 1
• The American Diabetes Association recommends measuring B12 levels in patients with peripheral neuropathy or unexplained anemia, not isolated language dysfunction 1
• B12-related cognitive features would more likely present with global cognitive impairment, not selective language dysfunction 1

Critical Next Steps

Immediate Diagnostic Workup

• Formal neuropsychological evaluation focusing on language domains to characterize the aphasia pattern 3
• Brain MRI to evaluate for selective atrophy of the language network, typically in the left anterior temporal lobe 2
• Check B12 levels given metformin use, though this is unlikely to be the primary diagnosis 1
• Montreal Cognitive Assessment (MoCA) rather than MMSE for more sensitive cognitive screening 5

Important Clinical Caveat

Do not attribute these symptoms solely to "normal aging" or diabetes-related cognitive decline—isolated progressive anomia requires thorough neurological workup to establish the diagnosis of PPA and determine the underlying neuropathology, which can include Alzheimer's disease or frontotemporal lobar degeneration 5, 1, 2