Overview & the 3 D's
Cognitive disorders affect memory, thinking, and awareness.
Cognitive disorders disrupt a person's memory, thinking, attention, and awareness. In older adults, three conditions can look alike but are managed very differently — the 3 D's:
- Delirium — acute and reversible
- Dementia — chronic and progressive
- Depression — can mimic dementia ("pseudodementia") but improves with treatment
Telling these apart is high-yield because two of the three are treatable. A sudden change in an older adult's mental status should always prompt a search for delirium's cause — never assume new confusion is "just dementia."
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Delirium
An acute, reversible medical emergency.
Delirium is a sudden disturbance in attention and awareness that develops over hours to days and tends to fluctuate (worse at some times than others). It is a symptom of an underlying medical problem and is usually reversible when that cause is treated.
Common Causes
- Infection — a urinary tract infection (UTI) is a classic trigger in older adults
- Medications and polypharmacy
- Dehydration and electrolyte imbalances
- Low oxygen (hypoxia), pain, and the post-operative/anesthesia period
Two Presentations
- Hyperactive — agitated, restless, may hallucinate
- Hypoactive — quiet, drowsy, withdrawn (often missed)
Because delirium is reversible, the priority is to identify and treat the underlying cause (treat the UTI, correct the electrolytes, review the meds) while keeping the client safe and reoriented. Sedating or restraining a delirious client without finding the cause can make outcomes worse.
Dementia
A chronic, progressive, irreversible decline.
Dementia is a gradual, progressive decline in memory and thinking severe enough to interfere with daily life. Unlike delirium, it develops slowly over months to years, is generally irreversible, and the level of consciousness stays clear until the late stages.
- Earliest and most prominent sign is usually short-term memory loss
- Progresses to problems with language, judgment, recognizing people/objects, and self-care
- The "3 A's" of decline often appear: amnesia (memory loss), aphasia (language), and apraxia (loss of learned movements), plus agnosia (not recognizing things)
In dementia, the client is usually alert — the problem is memory and thinking. In delirium, the level of consciousness itself fluctuates. If an alert client with known dementia suddenly becomes drowsy or wildly agitated, suspect a superimposed delirium and look for a new medical cause.
Alzheimer's Disease
The most common cause of dementia.
Alzheimer's disease is the most common form of dementia. It is a progressive, irreversible brain disorder that slowly destroys memory and thinking. It generally moves through stages:
- Earlymild
- Forgetfulness, especially recent memory; misplacing things; subtle word-finding trouble
- Middlemoderate
- Increasing confusion, wandering, sundowning, difficulty with names/tasks, needs cueing for self-care
- Latesevere
- Loss of language, immobility, incontinence, total dependence
Sundowning is increased confusion and agitation in the late afternoon/evening. Manage it by increasing light in the evening, keeping a calm consistent routine, reducing noise and stimulation, and avoiding late-day caffeine and naps.
Delirium vs Dementia
The comparison that shows up again and again on the exam.
- Onset
- Delirium: Acute (hours–days) · Dementia: Gradual (months–years)
- Course
- Delirium: Fluctuates · Dementia: Steady, progressive
- Reversible?
- Delirium: Yes (treat the cause) · Dementia: Generally no
- Consciousness
- Delirium: Altered, fluctuating · Dementia: Clear until late
- Attention
- Delirium: Markedly impaired · Dementia: Usually intact early
- Cause
- Delirium: Medical (infection, meds, etc.) · Dementia: Brain disease (e.g., Alzheimer's)
? An older adult with known dementia suddenly becomes confused and agitated this afternoon. Is this likely delirium or dementia?
Other Types of Dementia
Alzheimer's is the most common, but not the only one.
- Vascular dementia
- Caused by strokes/poor blood flow; often a stepwise decline
- Lewy body dementia
- Visual hallucinations and parkinsonism (tremor, rigidity)
- Frontotemporal
- Early personality and behavior changes
You don't need to diagnose the subtype — focus on recognizing dementia as chronic and progressive, distinguishing it from delirium, and providing safe, supportive nursing care. The subtype mostly affects the medical work-up, not the bedside nursing priorities.
Nursing Care & Communication
Safety, routine, and how you talk to the client.
Communication
- Approach from the front; use the client's name; calm, reassuring tone
- Short, simple sentences; one instruction at a time; allow extra time
- Use redirection and validation rather than arguing with a mistaken belief
- Keep a consistent routine and familiar environment
Delirium vs Dementia Focus
- Delirium: frequently reorient, provide a clock/calendar and familiar objects, ensure glasses/hearing aids, adequate lighting, and minimize stimulation while the cause is treated.
- Dementia: reorientation can frustrate the client — instead redirect and validate feelings, simplify the environment, and maintain routine.
For a client with dementia who insists on something untrue (for example, that they need to "go to work"), arguing increases agitation. Redirection ("Let's have a cup of tea first") and acknowledging the feeling behind the statement are far more effective.
Safety & Caregiver Support
Protecting the client and supporting the family.
- Wandering — use alarms/identification, secure exits, and provide safe areas to move.
- Home safety — remove hazards, lower water-heater temperature, lock up medications and chemicals, good lighting, remove throw rugs (fall risk).
- Routine & orientation aids — clocks, calendars, labeled rooms, consistent caregivers.
- Caregiver support — caregiver burnout is real; provide education, respite resources, and support groups.
As cognition declines, clients lose awareness of danger. The nurse's top priority shifts toward safety — preventing falls, wandering, burns, and medication errors — while preserving as much independence and dignity as possible.
Key Medications
What slows decline — and what to use with caution.
- Cholinesterase inhibitorsdonepezil, rivastigmine, galantamine
- Mild–moderate Alzheimer's; may slow progression (do not cure)
- MemantineNMDA antagonist
- Moderate–severe Alzheimer's; can be combined with a cholinesterase inhibitor
- Antipsychotics
- Only for severe agitation/psychosis; boxed warning — increased death in older adults with dementia
- Treat the causedelirium
- Antibiotics for infection, correct electrolytes/oxygen, review meds — the real "treatment" for delirium
Anchor on the contrast: delirium = acute, reversible — find the cause; dementia = chronic, progressive — keep them safe and communicate well. Medications only slow Alzheimer's; they don't reverse it, and antipsychotics in dementia carry real risk.
Frequently Asked Questions
Common student questions on this topic.
What is the difference between delirium and dementia?
What commonly causes delirium in older adults?
What is sundowning?
How should a nurse communicate with a client who has dementia?
What medications are used for Alzheimer's disease?
What are the 3 D's in older adults?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
Cognitive Disorders Cheatsheet
One-page PDF — free download.