What assessments and investigations are required to diagnose dementia?

What You Need to Diagnose Dementia

To diagnose dementia, you must document three core elements: (1) cognitive or behavioral symptoms that interfere with work or daily activities, (2) objective evidence of decline from prior functioning, and (3) exclusion of delirium or major psychiatric disorder—this requires obtaining history from both the patient and a knowledgeable informant, performing objective cognitive testing, and obtaining structural brain imaging. 1

Essential Diagnostic Components

History Taking

• Obtain collateral history from a close friend or family member to corroborate cognitive decline and functional impairment, as patients often lack insight into their deficits. 2
• Document specific changes in daily activities (e.g., managing finances, medications, driving, household tasks) to establish functional decline. 1
• Review medications thoroughly, as polypharmacy can mimic or worsen cognitive symptoms. 3
• Assess for depression, which can present as pseudodementia and must be differentiated from true dementia. 1

Cognitive Domain Assessment

• Document impairment in at least two of five cognitive domains: memory, attention, language, visuospatial function, or executive function; personality and behavior changes (mood fluctuations, agitation, apathy, social withdrawal) count as one domain. 1
• Use brief screening tools initially: Mini-Cog, Memory Impairment Screen (MIS), or caregiver questionnaires to identify suspected impairment. 3
• When screening suggests impairment, perform detailed cognitive assessment using Montreal Cognitive Assessment (MoCA), Saint Louis University Mental Status (SLUMS), or Rowland Universal Dementia Assessment Scale (RUDAS)—these have higher sensitivity (>80%) for detecting mild cognitive impairment and early dementia than the older MMSE. 4, 3

When to Order Neuropsychological Testing

• Order formal neuropsychological testing when bedside examination is inconclusive—specifically when symptoms are reported but examination appears normal, or when you need to distinguish between normal aging, mild cognitive impairment, and early dementia. 1, 5
• Neuropsychological testing can predict progression to dementia with 80-100% accuracy and helps determine retained versus impaired abilities for care planning. 5

Physical Examination

• Perform thorough neurologic examination looking for focal abnormalities (suggesting stroke), movement disorders (suggesting Parkinson's disease dementia or Lewy body dementia), or gait disturbances. 2
• Assess vision and hearing, as sensory impairments can worsen apparent cognitive function. 3
• Evaluate cardiovascular status and nutritional state. 3
• Document functional abilities in activities of daily living to help differentiate dementia severity and exclude other conditions. 1

Laboratory Testing

• Order vitamin B12 and folate levels, thyroid function tests, complete blood count, and comprehensive metabolic panel to rule out reversible causes of cognitive impairment. 3

Brain Imaging

• Obtain structural brain imaging with non-contrast MRI (or CT if MRI unavailable or contraindicated) to identify reversible causes such as tumor, normal pressure hydrocephalus, subdural hematoma, or stroke, and to document patterns of atrophy. 1, 3, 2

When to Refer to a Dementia Specialist

Refer immediately for any of these red flags: 1

• Age of onset before 60 years
• Atypical cognitive features: aphasia, apraxia, or agnosia early in the course
• Sensorimotor dysfunction: cortical visual disturbances, movement disorders, or gait abnormalities
• Rapid progression within weeks to months (urgent referral)
• Fluctuating course suggesting delirium, Lewy body dementia, or vascular cognitive impairment
• Discrepancy between significant reported symptoms and normal examination findings

Advanced Diagnostic Testing (Specialist Level)

When diagnostic uncertainty persists after standard workup, specialists may employ: 1

• Fluorodeoxyglucose (FDG) PET imaging
• Cerebrospinal fluid analysis for amyloid-β42 and tau/phosphorylated-tau biomarkers
• Amyloid PET scanning (applied according to appropriate-use criteria)
• Genetic testing with genetic counselor involvement for suspected autosomal-dominant familial dementia

Critical Diagnostic Pitfalls to Avoid

• Do not diagnose dementia based on single-domain impairment alone—at least two cognitive domains must be affected. 1
• Do not confuse depression (pseudodementia) with dementia, as depression can mimic cognitive impairment but is potentially reversible. 1
• Do not rely solely on brief screening tools like MMSE for diagnosis—these document severity but cannot establish the diagnosis without comprehensive clinical assessment. 4
• Do not skip obtaining informant history—patient self-report alone is insufficient due to lack of insight in dementia. 2