Alzheimer's Disease is the Most Likely Diagnosis
Based on this clinical presentation of insidious onset, gradual progression over years, predominant memory and executive dysfunction, absence of motor symptoms, and no stroke history, Alzheimer's disease is the most likely diagnosis.
Clinical Reasoning Based on Diagnostic Criteria
The patient's presentation matches the core diagnostic criteria for probable Alzheimer's disease dementia as defined by the most recent NIA-AA guidelines 1:
Key Features Supporting Alzheimer's Disease
Insidious onset with gradual progression over months to years is the hallmark of AD, distinguishing it from vascular dementia which typically shows sudden onset or stepwise decline 1
Memory impairment with executive dysfunction represents either the classic amnestic presentation or the executive dysfunction variant of AD, both of which are recognized presentations in the 2025 diagnostic criteria 1
Steady progressive course without sudden changes strongly supports a neurodegenerative process rather than vascular etiology 1
Absence of motor symptoms in early stages is characteristic of AD and specifically argues against dementia with Lewy bodies 1
Why Other Diagnoses Are Less Likely
Dementia with Lewy Bodies is excluded because the patient lacks core clinical features required for DLB diagnosis 2:
- No fluctuating cognition (pronounced variations in attention and alertness) 2
- No recurrent visual hallucinations (well-formed, detailed hallucinations of people, animals, or objects) 2
- No parkinsonism (bradykinesia, rigidity, tremor, postural instability) 2
- No REM sleep behavior disorder 2
Vascular dementia is unlikely because 1:
- No history of stroke temporally related to cognitive decline 1
- No sudden onset or stepwise deterioration pattern 1
- Gradual progression over years is atypical for pure vascular dementia 1
Frontotemporal dementia is not supported because 1:
- The patient lacks prominent behavioral changes, personality alterations, or language deficits that characterize behavioral variant FTD 1
- Memory and executive dysfunction as presenting features are more typical of AD than FTD 1
- FTD typically presents at younger ages (50s-60s) with behavioral disinhibition as the predominant early feature 1
Diagnostic Certainty Framework
According to the 2025 Alzheimer's Association guidelines, this clinical presentation meets criteria for probable AD dementia 1:
The insidious onset and clear progressive worsening establish the temporal pattern required for AD diagnosis 1
The combination of memory impairment and executive dysfunction represents recognized cognitive domain involvement in AD 1
The absence of features suggesting alternative diagnoses (no cerebrovascular disease, no core DLB features, no prominent FTD features) further supports AD as the primary diagnosis 1
Common Diagnostic Pitfalls to Avoid
Do not assume executive dysfunction automatically suggests frontotemporal dementia - executive dysfunction is a well-recognized non-amnestic presentation of AD and can be the most prominent deficit 1
Do not diagnose vascular dementia based solely on age and vascular risk factors - the temporal pattern (insidious vs. sudden, steady vs. stepwise) is critical for distinguishing AD from vascular dementia 1
Do not require memory impairment to be the sole or most prominent feature - the 2025 criteria explicitly recognize executive dysfunction, language, and visuospatial presentations as valid AD presentations 1
Role of Biomarkers in Increasing Diagnostic Certainty
While the clinical diagnosis is probable AD, biomarker testing could increase diagnostic certainty 1:
High likelihood of AD pathology if both amyloid-beta (PET or CSF) and neuronal injury markers (structural MRI, FDG-PET, CSF tau) are positive 1
Low likelihood of AD if both biomarker categories are negative, suggesting alternative pathology 1
Biomarkers are particularly useful when the clinical presentation is atypical or when multiple pathologies may coexist 1