Mild cognitive impairment (MCI) — objective cognitive decrement on testing without functional impairment severe enough to meet dementia criteria — is the diagnostic clarity point in the cognitive decline pathway. The diagnosis matters because it identifies the population at substantially elevated conversion risk (roughly 10-15% per year to Alzheimer's or other dementia), warrants aggressive prevention engagement, and increasingly opens consideration of disease-modifying treatment (Stage 24.4). The clinical task is detailed workup, subtype identification, and integrated treatment planning.
The diagnostic criteria. Cognitive complaint from patient or informant. Objective cognitive impairment on testing (typically more than 1.5 standard deviations below age-adjusted norms in at least one domain). Preserved functional independence — basic activities of daily living unimpaired; some difficulty with complex tasks may be present. Not meeting dementia criteria. The distinction from SCD is the objective testing decrement; the distinction from dementia is the preserved overall function.
MCI subtypes have different implications. Amnestic MCI — memory predominant impairment; higher conversion to Alzheimer's disease. Non-amnestic MCI — other cognitive domains predominant (executive function, visuospatial, language); broader differential including Lewy body, frontotemporal, vascular cognitive impairment. Single-domain versus multi-domain — multi-domain has higher conversion risk. The subtyping matters for both prognosis and for biomarker workup considerations.
The workup. Detailed history including family history. Neuropsychological testing to characterize the cognitive profile and confirm objective impairment. Medical workup: thyroid panel, B12, vitamin D, syphilis (rare but treatable), HIV in appropriate contexts, basic metabolic panel. Neuroimaging — MRI typically; CT if MRI not available. Consider neurology referral for full evaluation. Consider biomarker testing where appropriate (blood-based amyloid markers emerging; CSF or PET in specialty workup; APOE genetic testing — Stage 23.2). Sleep evaluation if any indication. Depression and anxiety assessment given high comorbidity.
The treatment and management. Address any reversible contributors identified in workup. Aggressive engagement with Modifiable Twelve factors. Cognitive training consideration (BrainHQ — Stage 20.4). Treatment of any mood, anxiety, or sleep disorder. Cardiovascular and metabolic optimization. Driving safety evaluation appropriate at this stage. Advance care planning conversation appropriate to begin. Consider anti-amyloid therapy if amnestic MCI with amyloid-positive biomarkers (Stage 24.4). Longitudinal monitoring with annual or more frequent reassessment. The discipline is to engage MCI as the clarity point in cognitive decline — diagnose carefully, characterize subtype, address reversible contributors aggressively, engage prevention work seriously, and integrate the broader clinical and family conversations that the diagnosis warrants.