A 68-year-old woman is evaluated in the outpatient neurology clinic for cognitive concerns. Her daughter reports that over the past 18 months, the patient has gradually become forgetful, has difficulty managing finances, and occasionally gets lost in familiar places. She is alert and oriented during the consultation, maintains good attention throughout the 30-minute visit, and does not hallucinate. Vital signs are normal. Mini-Cog score is 2/3. What is the most likely diagnosis, and what is the key clinical feature that excludes delirium?

Explanation

## Diagnosis: Dementia with Preserved Attention ### Why This Is Dementia, Not Delirium **Key Point:** The **insidious onset over 18 months** and **preserved attention during the 30-minute consultation** are the two critical features that define dementia and exclude delirium. ### Delirium vs Dementia: Feature Comparison | Feature | Delirium | Dementia | |---------|----------|----------| | **Onset** | Acute (hours–days) | Insidious (months–years) | | **Attention/Concentration** | **Severely impaired** — cannot focus, easily distracted | **Relatively preserved** — can attend to tasks | | **Consciousness Level** | Fluctuating; altered sleep-wake cycle | Alert and awake (until late stages) | | **Course** | Fluctuating hour-to-hour or day-to-day | Steady, progressive decline | | **Reversibility** | Often reversible with treatment | Irreversible | | **Hallucinations** | Common, vivid, often frightening | Uncommon; late feature | | **Vital Signs** | Often abnormal (fever, tachycardia) | Usually normal | **High-Yield:** If attention is **preserved** and onset is **insidious**, think **dementia**. If attention is **impaired** and onset is **acute**, think **delirium**. ### Clinical Pearl The patient maintained attention throughout a 30-minute clinic visit — this is incompatible with delirium. Delirium patients cannot sustain focus; they are distractible, disorganized, and often unable to cooperate with examination. The normal vital signs and absence of hallucinations further support dementia over delirium. ### Why Mild Cognitive Impairment Is Not the Answer While MCI is a valid diagnosis, the Mini-Cog score of 2/3 (abnormal; normal is 3/3) and functional decline (unable to manage finances, getting lost in familiar places) indicate that this patient has crossed the threshold from MCI to dementia. Dementia requires cognitive impairment that interferes with activities of daily living. **Mnemonic: DEMENTIA** — Key features of dementia: - **D**ecline in cognition (memory, language, visuospatial, executive) - **E**tiology: neurodegenerative (Alzheimer's, Lewy body, frontotemporal, vascular) - **M**onths to years onset - **E**arly: preserved attention and consciousness - **N**o hallucinations (unless Lewy body) - **T**raditional: progressive, irreversible - **I**nsidious presentation - **A**ctivities of daily living impaired [cite:DSM-5 Diagnostic Criteria for Major Neurocognitive Disorder; Harrison 21e Ch 41]