What are the recommended steps and criteria for diagnosing dementia?

Diagnosis of Dementia: A Structured Approach

The diagnosis of dementia requires a systematic assessment that includes history-taking from both patient and informant, objective cognitive testing, functional assessment, and appropriate laboratory and imaging studies to rule out reversible causes.

Core Diagnostic Criteria for Dementia

Dementia is diagnosed when there are cognitive or behavioral symptoms that:

1. Interfere with ability to function at work or usual activities
2. Represent a decline from previous levels of functioning
3. Are not explained by delirium or major psychiatric disorder
4. Are detected through history-taking and objective cognitive assessment 1

Required Cognitive/Behavioral Impairment

At least one of the following cognitive domains must be impaired:

• Memory impairment - repetitive questions, misplacing belongings, forgetting events
• Impaired reasoning/judgment - poor safety awareness, financial mismanagement
• Visuospatial deficits - inability to recognize faces/objects, disorientation
• Language impairment - word-finding difficulties, speech errors
• Personality/behavior changes - mood fluctuations, apathy, social withdrawal 1

Diagnostic Assessment Algorithm

Step 1: Initial Screening and History

• Obtain history from both patient and knowledgeable informant 1
• Document specific examples of cognitive decline and functional impairment
• Assess for risk factors and warning signs:
  • Missed appointments
  • Difficulty following instructions or taking medications
  • Decline in self-care
  • New-onset behavioral changes 1

Step 2: Cognitive Assessment

• Rapid screening tools (when time is limited):

  • Mini-Cog
  • Memory Impairment Screen (MIS) + Clock Drawing Test
  • Four-item version of MoCA 1, 2

• Comprehensive assessment tools (preferred when time permits):

  • Montreal Cognitive Assessment (MoCA) - more sensitive for mild impairment
  • Mini-Mental State Examination (MMSE)
  • Modified Mini-Mental State (3MS) examination 1, 2

Step 3: Functional Assessment

• Evaluate impact on activities of daily living (ADLs) and instrumental activities of daily living (IADLs)
• The distinction between mild cognitive impairment (MCI) and dementia hinges on functional impairment 1

Step 4: Laboratory Evaluation

• Complete blood count
• Comprehensive metabolic panel
• Thyroid function tests
• Vitamin B12 level
• Consider additional tests based on clinical presentation 2

Step 5: Neuroimaging

• Brain MRI or non-contrast CT to evaluate:
  • Structural causes
  • Vascular disease
  • Patterns of atrophy 2

Step 6: Differential Diagnosis

• Probable Alzheimer's Disease - gradual onset with documented progressive decline, predominantly amnestic presentation or nonamnestic variants (language, visuospatial, executive) 1

• Vascular Dementia - temporal relationship to stroke or presence of multiple infarcts/white matter disease 1

• Dementia with Lewy Bodies - core features beyond dementia itself 1

• Frontotemporal Dementia - prominent behavioral or language variants 1

Special Considerations

Ruling Out Confounding Factors

• Delirium - acute onset, fluctuating course, inattention
• Depression - can mimic or coexist with dementia
• Medication effects - particularly anticholinergics
• Sleep disorders - especially sleep apnea
• Sensory deficits - hearing or vision loss 1, 2

High-Risk Populations

Increased vigilance is warranted in patients with:

• History of stroke or TIA
• Late-onset depression
• Untreated sleep apnea
• Recent delirium
• First major psychiatric episode at advanced age
• Recent head injury
• Parkinson's disease 1

Management Considerations

For diagnosed Alzheimer's disease:

• Cholinesterase inhibitors (donepezil, galantamine, rivastigmine) for mild to severe dementia
• Memantine (alone or as add-on therapy) for moderate to severe dementia 2, 3

For Parkinson's disease dementia:

• Rivastigmine has demonstrated efficacy in improving cognitive performance 3

Common Pitfalls to Avoid

1. Failing to obtain collateral history - patients often lack insight into their deficits
2. Attributing cognitive decline to normal aging - dementia is not a normal part of aging
3. Missing potentially reversible causes - always evaluate for treatable conditions
4. Overlooking non-amnestic presentations - not all dementia presents with memory loss first
5. Relying solely on cognitive screening without functional assessment - functional impairment distinguishes dementia from MCI

By following this structured approach, clinicians can accurately diagnose dementia, identify its cause, and initiate appropriate management to improve quality of life and reduce morbidity and mortality.