What is the diagnostic approach for dementia?

Diagnosing Dementia

Dementia is diagnosed when cognitive or behavioral symptoms interfere with the ability to function at work or usual activities, represent a decline from previous functioning, and are not explained by delirium or major psychiatric disorder. 1, 2

Step 1: Obtain Corroborative History from an Informant

This is essential and has prognostic significance—never skip this step. 1, 3

• Document changes in three domains: cognition (repetitive questions, misplacing belongings, getting lost on familiar routes), function (managing finances, medications, transportation, household tasks, cooking, shopping), and behavior (mood fluctuations, agitation, impaired motivation) 1
• Use structured informant-based tools: AD8, IQCODE, ECog, or Lawton IADL Scale for functional assessment 1, 3
• For behavioral symptoms, use NPI-Q, MBI-C, GDS, or PHQ-9 1

Step 2: Assess Five Key Cognitive Domains

Evaluate each domain systematically through history and examination: 1

• Memory: Repetitive conversations, forgetting events/appointments 1
• Executive function: Poor judgment, inability to manage finances, poor decision-making, inability to plan complex activities 1
• Visuospatial abilities: Inability to recognize faces or common objects, difficulty operating simple implements, problems orienting clothing to body 1
• Language: Difficulty thinking of common words, hesitations, speech/spelling/writing errors 1
• Personality/behavior: Uncharacteristic mood fluctuations, agitation, impaired motivation 1

Step 3: Cognitive Screening Tools

Use the MoCA as your primary screening tool—it has superior sensitivity for mild cognitive impairment and early dementia compared to MMSE. 1

• MoCA is more sensitive than MMSE for detecting mild cognitive impairment and mild Alzheimer's disease 1, 2
• MMSE has >80% sensitivity and specificity for moderate dementia and is useful for longitudinal tracking 1, 3
• Add Clock Drawing Test as a supplementary screen for visuospatial and executive function 1, 3
• Do not diagnose dementia solely based on an impaired screening test result 1

Step 4: Core Laboratory Testing (Mandatory)

Order these tests to exclude reversible causes: 2, 3

• Complete blood count 2, 3
• Comprehensive metabolic panel (electrolytes, glucose, calcium, renal function, liver function) 2, 3
• Thyroid function tests (TSH, free T4) 2, 3
• Vitamin B12 level 2, 3
• Consider HIV testing if risk factors present 3
• Consider syphilis serology if clinically indicated 3

Step 5: Neuroimaging

MRI is preferred over CT, especially for detecting vascular lesions and atrophy patterns. 1

Specific indications for neuroimaging: 1

• Onset of cognitive symptoms within the past 2 years (regardless of progression rate) 1
• Unexpected and unexplained decline in cognition/function in a patient already known to have dementia 1
• Recent significant head trauma 1
• Unexplained neurological manifestations (new severe headache, seizures, Babinski sign, gait disturbances) 1
• History of cancer (particularly at risk for brain metastases) 1
• Subject at risk for intracranial bleeding 1
• Symptoms compatible with normal pressure hydrocephalus 1
• Significant vascular risk factors 1

If MRI is performed, use these sequences: 1

• 3D T1 volumetric sequence with coronal reformations for hippocampal volume assessment 1
• FLAIR 1
• T2 or susceptibility-weighted imaging (SWI) 1
• Diffusion-weighted imaging (DWI) 1

Use semi-quantitative scales for interpretation: 1

• Medial temporal lobe atrophy (MTA) scale for medial temporal involvement 1
• Fazekas scale for white matter changes 1
• Global cortical atrophy (GCA) scale to qualify global atrophy 1

Step 6: When to Consider Neuropsychological Testing

Order formal neuropsychological testing when: 2, 4

• Routine history and bedside mental status examination cannot provide a confident diagnosis 1
• Patient presentation is complex or symptoms are mild/unusual 2
• Patient has educational extremes or language/cultural considerations 2
• Need to establish extent and severity of cognitive impairment objectively 4

Common Pitfalls to Avoid

• Failing to obtain corroborative history from an informant—this is the most critical error 1, 3
• Overlooking potentially reversible causes through inadequate laboratory testing 2
• Using a "shotgun approach" to diagnostic testing rather than a tiered, methodical approach 2
• Diagnosing dementia based solely on screening test scores without clinical correlation 1
• Mistaking dementia as part of normal aging—dementia always represents pathology 5

Follow-up and Monitoring

Schedule follow-up visits every 6-12 months for stable patients. 2, 3

At each visit, assess all four domains: 2, 4

• Cognition (using MMSE for longitudinal tracking) 3, 4
• Functional autonomy (using IQCODE or Lawton IADL Scale) 1, 3
• Behavioral symptoms (using NPI-Q, GDS, or PHQ-9) 1, 3
• Caregiver burden (using Zarit Burden Interview) 1

Special Scenario: Subjective Cognitive Decline

For patients with consistent subjective cognitive complaints but normal cognitive testing and no obvious IADL impairment: 1

• Perform standard dementia medical workup to identify reversible causes 1
• Assess for psychiatric symptoms, especially depression and anxiety 1
• If corroborative history is negative, provide reassurance and offer follow-up if deterioration occurs 1
• If corroborative history is positive, schedule annual follow-ups and consider referral to memory clinic 1