Mild Cognitive Impairment & Dementia Workup
Mild Cognitive Impairment & Dementia Workup
What You'll Learn
- MCI = objective cognitive decline (1–1.5 SD below mean) with preserved functional independence — annual conversion to dementia ~10–15%; amnestic MCI most likely to convert to AD
- MoCA is superior to MMSE for detecting MCI — includes executive/visuospatial tasks; MMSE has ceiling effect and misses early deficits
- Standard dementia workup (AAN): CBC, CMP, TSH, B12, structural neuroimaging — rule out reversible causes first
- MRI atrophy patterns localize the diagnosis: hippocampal = AD, frontal/temporal = FTD, occipital = DLB/PCA — Scheltens MTA scale for grading
- CSF biomarkers: decreased Aβ42 + increased p-tau = AD; Aβ42/40 ratio is more accurate than Aβ42 alone; ATN framework classifies by biomarker profile
- Blood-based biomarkers are emerging: p-tau217 is the most promising screening biomarker for AD pathology
- CDR is the most widely used staging tool — CDR 0.5 = MCI/very mild dementia; CDR-SB (sum of boxes) tracks progression in clinical trials
HighYield Pearls
- MCI = Petersen/NIA-AA core: patient/informant/clinician cognitive concern + objective impairment (1–1.5 SD) in ≥1 domain + preserved functional independence + does NOT meet dementia criteria — preserved ADLs is the line between MCI and dementia.
- Amnestic MCI (isolated memory loss) has the highest conversion rate to AD; overall MCI → dementia ~10–15%/year in clinic cohorts; ~15–20% revert to normal — always hunt reversible causes (depression, anticholinergics, B12, OSA).
- MoCA > MMSE for MCI — MoCA is a sensitive cognitive SCREEN, not a diagnostic staging test. Commonly cited impairment bands (e.g., ≥26 often called normal, lower scores raising concern; add 1 if ≤12 yr education) must be interpreted with age, education, language/culture, sensory status, and functional history — do NOT diagnose MCI or dementia from MoCA bands alone. MMSE has a ceiling effect and misses executive/visuospatial deficits.
- AAN core dementia workup: CBC, CMP, TSH, B12 + structural neuroimaging (MRI > CT) — rule out reversible causes first; consider RPR, HIV, autoimmune panel based on red flags.
- MRI atrophy patterns localize: hippocampal/MTL → AD; frontal/anterior temporal "knife-edge" → FTD; preserved hippocampi + occipital → DLB; parieto-occipital → PCA; ventriculomegaly out of proportion → NPH.
- FDG-PET signatures: temporoparietal + posterior cingulate hypometabolism → AD; frontal/anterior temporal → FTD; occipital with cingulate island sign → DLB.
- CSF AD signature: low Aβ42 (prefer Aβ42/40 ratio) + high p-tau181/217 + high t-tau; negative amyloid PET effectively rules out AD; positive scan does NOT confirm AD (~30% of normal elderly are amyloid+).
- Plasma p-tau217 is the best emerging blood biomarker for AD (~90% concordance with amyloid PET); ATN framework (A+T+ confirms AD pathology) defines AD biologically across preclinical → MCI due to AD → AD dementia.
- CDR staging: 0 normal, 0.5 = MCI/very mild dementia, 1 mild, 2 moderate, 3 severe; CDR-SB is primary endpoint in lecanemab/donanemab trials; FAST ≥7c qualifies for hospice.
- Anti-amyloid mAb (lecanemab, donanemab) requires amyloid+ biomarker + early symptomatic AD; APOE ε4 genotyping SHOULD be performed before treatment per FDA labels for ARIA risk counseling (ε4 homozygotes highest risk) — recommended, not an absolute prerequisite; if not performed, treatment is not automatically prohibited but ARIA counseling is incomplete. APOE is NOT a diagnostic test.
🔍 Quick ReferenceClinical / criteria · Bedside cognitive testing · Workup / biomarkers
Clinical / criteria
- Cognitive concern + objective impairment ≥1 domain + preserved ADLs + not dementia → MCI (Petersen / NIA-AA 2011)
- Isolated memory loss with intact function, high AD conversion → Amnestic MCI
- Subjective complaint with NORMAL objective testing → Subjective Cognitive Decline (SCD) — preclinical
- Significant cognitive decline interfering with independence, not delirium → Major neurocognitive disorder (DSM-5 dementia)
- "I don’t know" answers, acute onset, mood history → Pseudodementia (depression)
- Cues do NOT help recall (encoding/storage deficit) → Cortical/AD pattern; cues DO help → subcortical (VaD, PD, NPH)
- A+T+N+ on biomarkers → AD with neurodegeneration (NIA-AA ATN)
Bedside cognitive testing
- MoCA (sensitive cognitive screen, NOT a diagnostic staging test) → Best brief screen for MCI / executive dysfunction; commonly used cutoffs (e.g., ≥26 often called normal; lower scores raising concern) vary with age, education, language/culture, and functional history — do NOT diagnose MCI or dementia from MoCA bands alone
- MMSE ≤23/24 → Dementia screen (ceiling effect — misses MCI)
- 3-word recall + clock drawing → Mini-Cog (primary-care screen)
- Trail Making B, verbal fluency (FAS), Luria fist-edge-palm, Go/no-go → Executive / frontal probes
- Clock drawing, Rey figure copy, pentagons, intersecting circles → Visuospatial / parietal probes
- Boston Naming Test, category fluency (animals), Token Test → Language battery (PPA work-up)
- RAVLT / CVLT / Logical Memory → Episodic memory (hippocampal / AD)
- CDR 0.5 → MCI / very mild dementia; FAST ≥7c → hospice eligibility
Workup / biomarkers
- CBC + CMP + TSH + B12 + MRI → AAN core dementia workup
- MTL/hippocampal atrophy (Scheltens MTA ≥2) → AD; preserved hippocampi + visual hallucinations → DLB
- Anterior temporal "knife-edge" / temporal pole scooped out → svPPA; frontal/insular atrophy → bvFTD/nfvPPA
- Cortical ribboning + caudate/putamen DWI signal → CJD; Evans index >0.3 + DESH → NPH
- Temporoparietal + posterior cingulate FDG hypometabolism → AD; cingulate island sign → DLB
- Low CSF Aβ42 + low Aβ42/40 ratio + high p-tau181/217 → AD-pattern CSF
- RT-QuIC positive (>90% sens, ~99% spec); t-tau/p-tau ratio >20 → CJD
- Plasma p-tau217-based assays → Best-performing blood biomarkers for AD pathology; Fujirebio Lumipulse G pTau217/Aβ42 Plasma Ratio is the first FDA-cleared blood test (cognitively impaired adults in specialty care — not a stand-alone screen); PrecivityAD2 / ALZpath / Quanterix are clinically used and validated as LDTs but are NOT FDA-cleared
- Abnormal DaTscan (reduced striatal uptake) → DLB / PDD (normal in AD)
- APOE ε4 homozygote → Highest ARIA risk before lecanemab/donanemab; C9orf72 hexanucleotide repeat → FTD-ALS; PSEN1 → earliest-onset autosomal dominant AD
Subjective Cognitive Decline (SCD)
- SCD (preclinical): subjective cognitive decline with normal objective testing and preserved function
- ~2× risk of progression to MCI/dementia compared to no SCD
- Particularly concerning ("SCD-plus" features; Jessen 2014 SCD-I) if:
- Persistent over time
- Age >60
- Onset <5 years ago
- Concern about memory specifically (rather than other domains)
- Informant corroboration
- Sits on the cognitive continuum: SCD → MCI → dementia; not all SCD progresses, but it identifies a higher-risk cohort for surveillance
MCI: Definition & Diagnostic Criteria
Core Diagnostic Features (Petersen criteria / NIA-AA 2011)
- Subjective cognitive concern — reported by patient, informant, or clinician
- Objective cognitive impairment — performance 1–1.5 SD below age/education-adjusted norms in ≥1 cognitive domain
- Preserved functional independence — may have mild difficulties with complex IADLs, but fundamentally independent
- Does NOT meet criteria for dementia — impairment does not significantly interfere with daily functioning
- DSM-5 terminology: mild neurocognitive disorder (vs. major neurocognitive disorder = dementia) — a related but not identical construct (1–2 SD threshold; informant or clinician concern; modest cognitive decline)
MCI Subtypes
| Subtype | Domains Affected | Most Likely Etiology |
|---|---|---|
| Amnestic — single domain | Memory only | AD (highest conversion rate) |
| Amnestic — multi-domain | Memory + ≥1 other domain | AD, vascular, mixed |
| Non-amnestic — single domain | One non-memory domain (e.g., executive, language) | FTD, DLB, vascular, psychiatric |
| Non-amnestic — multi-domain | ≥2 non-memory domains | Vascular, DLB, FTD |
MCI Prognosis
- Annual conversion to dementia: ~10–15%/year in specialty clinic / amnestic MCI cohorts; ~5–10%/year in community cohorts; lower for non-amnestic subtypes (vs. 1–2% in age-matched controls)
- ~30–50% of MCI patients progress to dementia within 5 years
- ~15–20% may revert to normal cognition (especially if depression, medication, or sleep disorder was the cause)
- Predictors of conversion: amnestic subtype, APOE ε4, positive amyloid biomarkers, hippocampal atrophy, lower baseline MoCA
AAN 2018 MCI Management Recommendations (Petersen)
- Recommend regular exercise (Level B; ≥2×/week) — the only intervention with a positive evidence-based recommendation for cognitive benefit in MCI
- Optimize vascular risk factors — BP, lipids, glucose, smoking cessation, diet
- Cognitive training may be considered — modest evidence; reasonable to discuss with patients
- NO FDA-approved medications for MCI; cholinesterase inhibitors are NOT routinely recommended (no proven benefit in delaying conversion to dementia)
- Re-evaluate cognition every 6–12 months — track for progression, reversion, or stability
- Discuss prognosis including potential for reversion (~15–20%) and conversion risk; address advance planning while capacity is intact
💎 Board Pearl
- Amnestic MCI has the highest conversion rate to AD — if the board describes isolated memory loss with preserved function, this is the diagnosis
- MCI is a clinical diagnosis — biomarkers add certainty but are not required; preserved functional independence is the key distinguishing feature from dementia
- ~15–20% of MCI patients revert to normal — always look for reversible causes (depression, medications, OSA, B12 deficiency)
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