What are the diagnostic criteria for Mild Cognitive Impairment (MCI)?

Diagnostic Criteria for Mild Cognitive Impairment (MCI)

Mild Cognitive Impairment (MCI) is defined by mildly impaired performance on neuropsychological cognitive tests with minimal impact on daily functioning, characterized by specific clinical and cognitive criteria that distinguish it from normal aging and dementia. 1

Core Clinical Criteria for MCI Diagnosis

Essential Components:

1. Cognitive Concern

   • Evidence of concern about a change in cognition compared to previous level
   • Concern may be reported by:
     • Patient themselves
     • Knowledgeable informant
     • Skilled clinician observing the patient 1

2. Objective Cognitive Impairment

   • Evidence of lower performance in one or more cognitive domains
   • Performance decline greater than expected for patient's age and education
   • Decline should be evident over time if serial assessments are available
   • Affected domains may include:
     • Memory (especially episodic memory)
     • Executive function
     • Attention
     • Language
     • Visuospatial skills 1

3. Preserved Functional Independence

   • Maintenance of independence in daily activities with minimal aids/assistance
   • May have mild problems with complex functional tasks (e.g., bill paying, meal preparation)
   • May take more time, be less efficient, or make more errors than previously 1

4. Not Demented

   • Cognitive changes insufficiently severe to constitute dementia
   • No significant impairment in social or occupational functioning 1

MCI Subtypes

MCI can be categorized into four subtypes based on memory involvement and number of affected domains 2:

1. Amnestic MCI, Single Domain

   • Memory impairment only

2. Amnestic MCI, Multiple Domain

   • Memory impairment plus deficits in other cognitive domains

3. Non-amnestic MCI, Single Domain

   • Impairment in a non-memory domain only (e.g., language, visuospatial)

4. Non-amnestic MCI, Multiple Domain

   • Impairment in multiple non-memory domains

Etiological Classification of MCI

When considering the likelihood of MCI being due to Alzheimer's Disease (AD), the following categories apply 1:

1. MCI - Core Clinical Criteria

   • Meets basic MCI criteria without biomarker testing
   • Typically shows prominent episodic memory impairment if likely to progress to AD

2. MCI due to AD - Intermediate Likelihood

   • Meets core MCI criteria
   • Has either positive biomarker for Aβ deposition OR positive biomarker for neuronal injury

3. MCI due to AD - High Likelihood

   • Meets core MCI criteria
   • Has positive biomarkers for BOTH Aβ deposition AND neuronal injury

4. MCI - Unlikely due to AD

   • Negative biomarkers for both Aβ deposition and neuronal injury
   • Warrants search for alternative causes

Diagnostic Evaluation Process

1. Clinical Assessment

   • Document cognitive concerns from patient/informant
   • Assess for changes in cognition over time
   • Rule out delirium or major psychiatric disorders 1

2. Cognitive Testing

   • Formal neuropsychological testing or bedside cognitive assessment
   • Evaluate multiple cognitive domains
   • Compare to age and education-appropriate norms 1

3. Functional Assessment

   • Evaluate independence in activities of daily living
   • Assess ability to perform complex instrumental activities 1

4. Etiological Investigation

   • Rule out vascular, traumatic, medical causes of cognitive decline
   • Consider genetic factors when relevant
   • Assess for longitudinal decline in cognition when possible 1

5. Biomarker Testing (primarily in research settings)

   • Biomarkers of Aβ deposition:
     • CSF Aβ42
     • PET amyloid imaging
   • Biomarkers of neuronal injury:
     • CSF tau/phosphorylated-tau
     • Hippocampal volume or medial temporal atrophy
     • FDG-PET imaging
     • SPECT perfusion imaging 1

Clinical Pitfalls and Caveats

1. Diagnostic Boundaries

   • Sharp demarcations between normal cognition, MCI, and dementia are difficult
   • Clinical judgment is essential in making these distinctions 1

2. Heterogeneity

   • MCI is heterogeneous in etiology and clinical presentation
   • Not all MCI progresses to dementia; some cases remain stable or improve 3

3. Functional Assessment Challenges

   • Determining preserved functional independence requires knowledge of the individual's previous level of function
   • Cultural and educational factors may influence functional assessment 1

4. Biomarker Limitations

   • Biomarker use is currently recommended primarily for research settings
   • Limited standardization of biomarkers across different locations
   • Variable access to biomarker testing 1

5. Prognostic Uncertainty

   • Many people with MCI will improve, and most will not progress to dementia
   • Limited evidence for effective interventions 3

By systematically applying these diagnostic criteria, clinicians can identify individuals with MCI and provide appropriate monitoring and management to potentially improve outcomes related to morbidity, mortality, and quality of life.