What are the diagnostic criteria for dementia in an elderly patient with a history of cognitive decline?

Diagnostic Criteria for 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 levels of functioning, and are not explained by delirium or major psychiatric disorder. 1

Core Diagnostic Requirements

The diagnosis requires all three of the following elements 1:

1. Functional interference: Cognitive or behavioral symptoms must interfere with work or usual activities 1
2. Documented decline: Symptoms represent a decline from previous levels of functioning and performing 1
3. Exclusion of other causes: Not explained by delirium or major psychiatric disorder 1

Cognitive Domain Involvement

At minimum, impairment must involve two or more of the following five cognitive domains 1:

1. Memory (Impaired ability to acquire and remember new information)

• Repetitive questions or conversations 1
• Misplacing personal belongings 1
• Forgetting events or appointments 1
• Getting lost on familiar routes 1

2. Executive Function (Impaired reasoning, complex tasks, poor judgment)

• Poor understanding of safety risks 1
• Inability to manage finances 1
• Poor decision-making ability 1
• Inability to plan complex or sequential activities 1

3. Visuospatial Abilities

• Inability to recognize faces or common objects 1
• Cannot find objects in direct view despite good acuity 1
• Inability to operate simple implements 1
• Cannot orient clothing to the body 1

4. Language Functions (Speaking, reading, writing)

• Difficulty thinking of common words while speaking 1
• Speech hesitations 1
• Speech, spelling, and writing errors 1

5. Personality, Behavior, or Comportment Changes

• Uncharacteristic mood fluctuations such as agitation 1
• Impaired motivation, initiative, apathy, loss of drive 1
• Social withdrawal, decreased interest in previous activities 1
• Loss of empathy 1
• Compulsive or obsessive behaviors 1
• Socially unacceptable behaviors 1

Detection and Diagnosis Process

Cognitive impairment must be detected through both 1:

1. History taking from the patient AND a knowledgeable informant 1
2. Objective cognitive assessment: Either bedside mental status examination (e.g., MMSE, MoCA) or neuropsychological testing 1

When to Use Neuropsychological Testing

Neuropsychological testing should be performed when routine history and bedside mental status examination cannot provide a confident diagnosis 1

Recommended Cognitive Screening Tools

For comprehensive assessment, use 1, 2:

• Montreal Cognitive Assessment (MoCA): More sensitive for mild cognitive impairment; recommended when mild impairment is suspected or MMSE is in "normal" range (24+/30) 1
• Mini-Mental State Examination (MMSE): Most widely validated; high sensitivity and specificity for moderate dementia; cut-point of 23/24 or 24/25 demonstrates reasonable sensitivity and specificity 1, 2
• Modified Mini-Mental State (3MS): More comprehensive than MMSE 1

For rapid screening (when time is limited) 1:

• Memory Impairment Screen (MIS) + Clock Drawing Test 1
• Mini-Cog 1
• AD8 questionnaire 1
• Four-item version of MoCA (Clock-drawing, Tap-at-letter-A, Orientation, Delayed-recall) 1

Essential Informant Assessment

Informant report is mandatory because patients often lack insight into their cognitive, functional, and behavioral changes 1. Use standardized tools 1:

• For cognitive changes: ECog 1
• For cognitive and functional changes: AD8, IQCODE, Quick Dementia Rating System (QDRS) 1
• For functional changes: Pfeffer Functional Activities Questionnaire (FAQ), Lawton-Brody IADL, 4-item IADL scale 1
• For behavioral changes: Neuropsychiatric Inventory-Questionnaire (NPI-Q), Mild Behavioural Impairment Checklist (MBI-C) 1

Differentiation from Mild Cognitive Impairment

The key distinction between MCI and dementia is functional independence 1:

• MCI: Preservation of independence in functional abilities; cognitive deficits do not interfere with capacity for independence in everyday activities (though greater effort or compensatory strategies may be required) 1
• Dementia: Cognitive or behavioral symptoms interfere with ability to function at work or usual activities 1

Common Diagnostic Pitfalls

Avoid these critical errors 1, 3:

• Relying solely on patient self-report without informant corroboration leads to missed diagnoses due to lack of insight 3
• Failing to use standardized, validated instruments reduces diagnostic accuracy and makes longitudinal tracking unreliable 3
• Overlooking that MMSE lacks sensitivity for mild dementia or MCI 1
• Not combining cognitive tests with functional screens and informant reports, which significantly improves diagnostic accuracy 1