What are the diagnostic criteria for dementia?

Dementia Diagnostic Criteria

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, are not explained by delirium or major psychiatric disorder, and involve impairment in at least two cognitive domains. 1

Core Clinical Criteria for All-Cause Dementia

The diagnosis requires three essential elements 1:

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

Cognitive Domain Assessment

Cognitive impairment must be detected through both history-taking from the patient and a knowledgeable informant AND objective cognitive assessment (bedside mental status examination or neuropsychological testing). 1 Neuropsychological testing should be performed when routine history and bedside examination cannot provide a confident diagnosis. 1

The cognitive or behavioral impairment must involve a minimum of two of the following five domains 1:

1. Memory Impairment

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

2. Executive Dysfunction

• 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 Impairment

• Inability to recognize faces or common objects despite good acuity 1
• Inability to find objects in direct view 1
• Inability to operate simple implements 1
• Inability to orient clothing to the body 1

4. Language Dysfunction

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

5. Behavioral/Personality Changes

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

Diagnostic Assessment Algorithm

Step 1: Clinical History

Obtain detailed information about cognitive concerns from both the patient AND a knowledgeable informant, focusing on onset, progression pattern, and impact on instrumental activities of daily living (managing finances, medications, transportation, household tasks). 1, 2, 3 This corroborative history is essential for accurate diagnosis. 2, 3

Step 2: Objective Cognitive Testing

Use standardized cognitive screening tools, with the Mini-Mental State Examination (MMSE) having high sensitivity for moderate dementia, while the Montreal Cognitive Assessment (MoCA) is more sensitive for mild cognitive impairment. 2, 3, 4 The Mini-Cog test and Addenbrooke's Cognitive Examination-Revised (ACE-R) have comparable diagnostic performance to the MMSE. 4

Step 3: Laboratory Evaluation

Perform core laboratory tests including complete blood count, comprehensive metabolic panel, thyroid function tests, vitamin B12 level, and calcium levels to exclude reversible causes. 2, 3, 5

Step 4: Neuroimaging

Obtain anatomical neuroimaging (MRI preferred over CT) particularly when cognitive symptom onset is within the past 2 years, there is unexpected decline, recent significant head trauma, unexplained neurological manifestations, or significant vascular risk factors. 2, 3, 5

Critical Distinction from Mild Cognitive Impairment

The differentiation of dementia from MCI rests on whether there is significant interference in the ability to function at work or in usual daily activities. 1 This is a clinical judgment made by a skilled clinician based on individual patient circumstances and descriptions from both patient and informant. 1

Common Pitfalls to Avoid

• Failing to obtain corroborative history from an informant is a major diagnostic error, as patients with dementia often lack insight into their deficits 2, 3
• Overlooking potentially reversible causes such as metabolic disturbances, medication effects, depression, or delirium that can mimic dementia 2, 3
• Mistaking normal aging for dementia or vice versa requires careful assessment of functional decline 6
• Using a "shotgun approach" to testing rather than a methodical, tiered approach wastes resources and may confuse the clinical picture 2

Important Nuances

Memory impairment is NOT always the primary deficit in dementia. 1 Nonamnestic presentations can occur, particularly with onset before age 65, including language-predominant (logopenic aphasia), visuospatial-predominant (posterior cortical atrophy), or executive dysfunction-predominant presentations. 1

In patients aged 80 or older, more than one cause of dementia is often present (e.g., Alzheimer disease plus vascular dementia), requiring careful evaluation of multiple contributing factors. 7