How can I differentiate between Alzheimer's disease and other types of dementia during initial assessments?

During initial assessments in a non-specialist setting, such as General Practice, the primary focus is to identify suspected dementia and rule out reversible causes of cognitive decline, rather than differentiating between specific dementia subtypes like Alzheimer's disease ¹,².

Initial Assessment in General Practice:

• History Taking: Obtain a history from the person with suspected dementia and, if possible, from someone who knows them well (e.g., a family member), covering cognitive, behavioural, and psychological symptoms, and their impact on daily life ¹.
• Physical Examination and Tests: If dementia is still suspected after history taking, conduct a physical examination and undertake appropriate blood and urine tests to exclude reversible causes of cognitive decline, such as delirium, depression, sensory impairment, or medication-related cognitive impairment ¹,².
• Cognitive Testing: Use a validated brief structured cognitive instrument, such as the 10-point cognitive screener (10-CS), 6-item cognitive impairment test (6CIT), or Test Your Memory (TYM) ¹. It is important to note that dementia should not be ruled out solely based on a normal score on a cognitive instrument ¹.
• Referral: If reversible causes have been investigated and dementia is still suspected, refer the person to a specialist dementia diagnostic service, such as a memory clinic or community old age psychiatry service ¹,². For suspected rapidly progressive dementia, refer to a neurological service ¹,².

Differentiation in Specialist Dementia Diagnostic Services:

The diagnosis of a dementia subtype, including Alzheimer's disease, typically occurs in specialist services after initial assessment confirms cognitive decline and reversible causes have been ruled out ¹.

• Verbal Episodic Memory: If Alzheimer's disease is suspected by the specialist, a test of verbal episodic memory should be included in the assessment ¹.
• Neuropsychological Testing: Neuropsychological testing may be considered if it is unclear whether the person has cognitive impairment, if their cognitive impairment is caused by dementia, or what the correct subtype diagnosis is ¹.
• Validated Criteria: Specialists use validated criteria, such as the National Institute on Aging (NIA) criteria for Alzheimer's disease, to guide clinical judgment when diagnosing dementia subtypes ¹.
• Structural Imaging: Structural imaging (MRI or CT scan) is offered to rule out reversible causes and assist with subtype diagnosis, unless dementia is well established and the subtype is clear ¹,². Alzheimer's disease should not be ruled out based solely on CT or MRI scan results ¹.
• Further Tests (if diagnosis uncertain): If the diagnosis is uncertain and Alzheimer's disease is suspected, specialists may consider further tests such as FDG-PET (fluorodeoxyglucose-positron emission tomography-CT) or perfusion SPECT (single-photon emission CT), or examining cerebrospinal fluid for total tau, phosphorylated-tau 181, amyloid beta 1–42, or amyloid beta 1–40 ¹,².
• Tests Not Recommended: Apolipoprotein E genotyping or electroencephalography should not be used to diagnose Alzheimer's disease ¹.