What is the diagnostic approach for dementia, including tests to order and methods to detect malingering?

Diagnosing Dementia: A Comprehensive Approach

The diagnosis of dementia requires a multidimensional assessment including standardized cognitive testing, informant reports, laboratory testing, and neuroimaging, with neuropsychological evaluation recommended for complex or atypical presentations. 1

Diagnostic Criteria

• Cognitive or behavioral symptoms must interfere with ability to function at work or usual activities, represent a decline from previous levels of functioning, and not be explained by delirium or major psychiatric disorder 2
• Diagnosis should be based on history from both patient and knowledgeable informant, plus objective cognitive assessment 2, 1
• Key cognitive domains affected include memory, reasoning, visuospatial abilities, language function, and changes in personality or behavior 2

Initial Assessment

• Obtain corroborative history from a reliable informant, which is essential for diagnostic accuracy 1
• Use standardized cognitive assessment tools:
  • Montreal Cognitive Assessment (MoCA) - more sensitive for mild cognitive impairment 2, 1
  • Mini-Mental State Examination (MMSE) - high sensitivity for moderate dementia 2, 3
  • Clock Drawing Test - useful supplementary test 1
• Assess functional status using informant-based tools:
  • Everyday Cognition (ECog) - measures informant's report of cognitive changes 1
  • AD8, IQCODE, or Quick Dementia Rating System (QDRS) - measure informant's report on cognitive and functional changes 1
  • Functional Assessment Questionnaire (FAQ) or Lawton-Brody IADL - measure functional changes 1
  • Neuropsychiatric Inventory Questionnaire (NPI-Q) or Mild Behavioral Impairment Checklist (MBI-C) - measure behavioral changes 1

Laboratory Testing (Tier 1)

• Complete blood count 4, 5
• Comprehensive metabolic panel including:
  • Electrolytes (sodium, potassium) 4, 5
  • Glucose 4, 5
  • Calcium 4, 6
  • Renal function (BUN, creatinine) 4, 5
  • Liver function tests 4, 7
• Thyroid function tests (TSH) 4, 5
• Vitamin B12 levels 4, 6

Neuroimaging (Tier 1)

• Non-contrast brain MRI (preferred) or CT scan if MRI is unavailable 4, 1
• Neuroimaging helps evaluate:
  • Patterns of atrophy (hippocampal and cortical) 4, 7
  • Vascular lesions such as infarcts 4, 8
  • Non-degenerative conditions (hydrocephalus, space-occupying lesions) 4, 7

Additional Testing for Complex Cases

• Neuropsychological evaluation is recommended when:
  • Patient's presentation is complex or atypical 1, 6
  • Symptoms are mild or unusual 1, 9
  • There are educational, language, or cultural considerations 1, 9
  • Patient has comorbidities that may present as cognitive impairment 1, 6
• Additional tests based on clinical suspicion (Tier 2):
  • Serology for syphilis or HIV 4, 7
  • Lipid profile 4
  • Inflammatory markers (ESR, CRP) 4, 1
  • HbA1c in suspected diabetes 4

Specialized Testing (Tier 3-4)

• For early-onset (<65 years) or rapidly progressive dementia:
  • Lumbar puncture with CSF analysis 4, 1
  • Advanced neuroimaging: PET scans with FDG or amyloid PET 4, 1

Detecting Malingering or Factitious Symptoms

• Look for inconsistencies between observed behaviors and test performance 9
• Compare self-reported symptoms with informant reports - significant discrepancies may suggest malingering 1
• Assess for patterns of performance that are inconsistent with known patterns of cognitive impairment in dementia 9
• Serial/longitudinal assessments can reveal inconsistent patterns over time that don't match expected progression of dementia 9, 1
• Neuropsychological testing can include specific validity measures to detect effort and motivation issues 1, 9
• Performance on very simple tasks should not be worse than on more complex tasks within the same cognitive domain 9

Follow-up and Monitoring

• For patients with subjective cognitive decline but normal testing:
  • Provide reassurance if there is negative corroborative history 1
  • Schedule annual follow-ups if there is positive corroborative history 1
• Track response to treatment and change over time using the same standardized tools at regular intervals (typically every 6-12 months) 1

Common Pitfalls to Avoid

• Diagnosis should not be based solely on impaired cognitive screening test results 1, 9
• Always rule out conditions that mimic dementia, such as depression, metabolic disturbances, medication effects, and sleep disorders 2, 6
• Standard cognitive screening tests (MMSE, MoCA) may not be sufficient to capture subtle changes in atypical dementia syndromes 1, 9
• Relying solely on patient self-report without informant input can lead to missed diagnoses 1
• Failure to consider cultural, educational, and language factors when interpreting cognitive test results 1, 9