What diagnostic approach should be taken to evaluate symptoms of cognitive decline and rule out dementia?

Diagnostic Approach to Rule Out Dementia

Initial Assessment: The Three-Domain Evaluation

To rule out dementia, you must systematically assess three mandatory domains using validated instruments: cognition, function, and behavior, combined with corroborative informant history—diagnosis cannot be made on cognitive testing alone. 1

Step 1: Obtain Corroborative History from Reliable Informant

• Informant report is essential because patients often lack insight into their cognitive, functional, and behavioral changes 1, 2
• Use structured informant-based tools to increase diagnostic accuracy:
  • AD8 (2-3 minutes): Yes/no questions about memory, orientation, judgment, and function 1
  • IQCODE: Rates change from premorbid baseline on cognitive abilities 1
  • QDRS: 10-item questionnaire rating change across cognitive, behavioral, and functional domains (7-10 minutes) 1
• Document whether symptoms represent insidious mid-to-late life onset versus acute changes 1
• Establish timeline of decline and impact on daily activities 3

Step 2: Cognitive Assessment with Validated Instruments

For comprehensive screening when time permits:

• MoCA (Montreal Cognitive Assessment): Most sensitive for mild cognitive impairment and mild dementia; use when MMSE is in "normal" range (24+/30) but suspicion remains 1, 4
• MMSE: High sensitivity/specificity for moderate dementia but lacks sensitivity for MCI 1, 4
• RUDAS: Comprehensive tool recommended when more time is available 1, 5

For rapid screening (when time is limited):

• Mini-Cog or MIS + Clock Drawing Test: Can be completed quickly with comparable diagnostic performance to MMSE 1, 4
• 4-item MoCA (Clock-drawing, Tap-at-letter-A, Orientation, Delayed-recall) 1

Critical caveat: Normal cognitive screening does not rule out dementia—if clinical suspicion persists with normal testing, refer for neuropsychological testing 1, 3

Step 3: Functional Assessment

Assess instrumental activities of daily living (IADLs) with patient AND informant:

• FAQ (Pfeffer Functional Activities Questionnaire) or DAD (Disability Assessment for Dementia) 1, 2
• Specifically evaluate: managing finances, medication management, transportation, household tasks, cooking, shopping 2
• Key distinction: Dementia requires significant interference with daily functioning; MCI does not 2

Step 4: Behavioral/Neuropsychiatric Assessment

Screen for behavioral and mood changes that may be early features:

• NPI-Q (Neuropsychiatric Inventory-Questionnaire) or MBI-C (Mild Behavioural Impairment Checklist) for behavioral symptoms 1, 2
• PHQ-9 if mood changes observed 1
• Probe specifically for: apathy, depression, anxiety, delusions, hallucinations, agitation, personality changes 1
• These symptoms may not be recognized by patient/informant as related to cognitive decline 1

Step 5: Laboratory Testing to Identify Reversible Causes

Essential screening tests for all patients:

• Thyroid function tests (TSH, free T4) 2, 6
• Vitamin B12 and folate levels 2, 6
• Complete blood count 6
• Comprehensive metabolic panel (sodium, calcium, glucose) 6
• HIV testing if risk factors present 2

These tests identified treatable causes in 11/200 patients in prospective studies, including hypothyroidism, hyponatremia, hyperparathyroidism, and hypoglycemia 6

Step 6: Neuroimaging

MRI is preferred over CT for detecting vascular lesions, focal atrophy, infarcts, and tumors that may not be identified on physical examination 2, 3, 7

Neuroimaging is especially indicated when:

• Onset of symptoms within past 2 years 2
• Unexpected decline in cognition/function 2
• Recent significant head trauma 2
• Unexplained neurological manifestations 2
• Significant vascular risk factors 2

Special Scenarios

Subjective Cognitive Decline (Normal Testing with Complaints)

If cognitive testing is normal but patient has consistent subjective complaints:

• Complete the standard dementia workup to identify reversible causes 1
• Assess for depression and anxiety using PHQ-9 and GAD-7 1
• Use structured scales: MoCA, SCD-Q, ECog, IQCODE, MBI-C, NPI-Q 1
• If informant corroborates decline: Annual follow-ups and consider referral to memory clinic 1
• If informant does NOT corroborate: Reassure and offer follow-up if deterioration occurs 1

Atypical Presentations

Consider DCQ (Dementia Cognitive Questionnaire) for screening atypical syndromes like behavioral variant frontotemporal dementia, primary progressive aphasia, or Alzheimer's disease variants—MMSE and MoCA were not designed for these 1

Consider CSF assays or genetic testing when:

• Age of onset younger than 65 years 3
• Rapid symptom onset 3
• Impairment in multiple cognitive domains but NOT episodic memory 3

Common Pitfalls to Avoid

• Never diagnose dementia based solely on impaired cognitive screening test results—you must document functional decline and obtain informant corroboration 1, 2
• Do not rely on patient self-report alone—lack of insight leads to missed diagnoses 2
• Do not overlook behavioral symptoms as unrelated—they may be the earliest manifestation of neurodegenerative disease 1
• Do not skip informant assessment—combining cognitive tests with functional screens and informant reports significantly improves diagnostic accuracy 1
• Do not assume normal MMSE rules out dementia—use MoCA when MCI or mild dementia is suspected 1, 4

Longitudinal Monitoring

If dementia is diagnosed, track progression using:

• Multi-dimensional assessment every 6-12 months (more frequently if behavioral symptoms present) 1, 2
• MMSE for tracking cognitive changes over time 1
• DAD or FAQ for functional changes 1
• NPI-Q for behavioral symptoms 1
• Serial assessments are more meaningful than single time-point evaluations 1