Cognitive Impairment and Dementia
Dementia is a syndrome, not a test score
Major neurocognitive disorder requires acquired, progressive cognitive decline in one or more domains that interferes with independence. Mild cognitive impairment (MCI) shows decline without functional loss. Common types: Alzheimer disease (memory-predominant), vascular (stepwise, executive), Lewy body (fluctuations, visual hallucinations, parkinsonism, REM sleep behavior disorder), frontotemporal (behavior or language), and reversible contributors (depression, thyroid disease, B12 deficiency, medications, sleep apnea, normal pressure hydrocephalus).
Assess cognition with Mini-Cog or MoCA, function with ADL/IADL history, and safety (driving, finances, medications). Interview a caregiver. Neuroimaging is not routine but helps with focal findings, rapid decline, or suspected NPH/vascular disease.
Traps: diagnosing dementia from a low MMSE alone without functional decline; missing delirium superimposed on dementia; attributing apathy to depression or vice versa; and stopping acetylcholinesterase inhibitors abruptly in moderate disease without reason. Antipsychotics are for severe agitation or psychosis and carry increased mortality in dementia.
Worked example: a 78-year-old with known Alzheimer disease becomes acutely confused and agitated after starting oxybutynin. Acute change plus inattention suggests delirium; stop the anticholinergic, look for infection, pain, and retention, and recheck cognition after recovery.
Rule of thumb: dementia is chronic and progressive; any acute fluctuation is delirium until proven otherwise.