Updated October 2025
Bedside Neurocognitive Differentiation
Delirium versus Dementia: Rapid Bedside Differentiation
Delirium is an acute, fluctuating disturbance in attention and awareness with altered arousal; dementia is a chronic, progressive decline in multiple cognitive domains with preserved arousal until late. At the bedside, prioritize assessments of attention/vigilance, level of arousal, temporal course, and fluctuation. Use structured tools (e.g., CAM variants, DRS-R-98) adapted for patients with baseline dementia and focus on tests of attention (digit span, months of the year backwards), vigilance (continuous performance), and visuospatial tasks that are disproportionately impaired in delirium. Accurate differentiation drives urgent reversible-cause workup and impacts long-term outcomes.
Clinical question
Which bedside features and brief tests best distinguish delirium from dementia, including delirium superimposed on dementia (DSD)?
DeliriumDementiaGeriatricsHospital MedicineNeurologyPalliative Care
Key points
Anchor on attention and arousal
Assess attention/vigilance first; abnormal attention with altered arousal strongly supports delirium, even with baseline dementia [1], [3], [2].
Identify acute and fluctuating course
Hours–days onset with waxing/waning cognition and consciousness is typical of delirium; dementia evolves over months–years [6], [7].
Use delirium-specific tools in dementia
DRS-R-98 and CAM-based approaches remain useful; attention items retain discriminative value in DSD [8], [9], [2].
Recognize prognostic weight
Delirium is linked to worse outcomes and accelerated cognitive decline; prioritize reversible-cause evaluation and prevention [4], [5], [10].
Beware hypoactive presentations
Hypoactive delirium is common in palliative/older adults and easily misattributed to dementia or depression [11], [6].
Evidence highlights
Inattention with acute fluctuation [1], [2]
Core distinguishing feature
Altered level of arousal favors delirium [3]
Arousal clue
↑ incident dementia ~5.4× after delirium [4], [5]
Delirium → dementia risk
Practical Differentiation in 5 Minutes
A structured micro-exam emphasizing attention, arousal, and fluctuation reliably separates delirium from dementia, including DSD.
1
1) Establish time course and fluctuation
Ask caregivers/nurses about abrupt onset (hours–days) and waxing/waning cognition or alertness. An acute, fluctuating course strongly indicates delirium; dementia changes are insidious and steady [6], [7].
2
2) Measure level of arousal
Use simple observation or a sedation scale. Reduced or elevated arousal (drowsy, hypervigilant) supports delirium; normal arousal is typical in most dementia until late stages [3].
3
3) Test attention and vigilance (core)
Administer months of the year backwards, digit span, or serial 7s; add a brief vigilance task (e.g., tap at letter ‘A’). Marked inattention and vigilance errors favor delirium, including in DSD [1], [12], [2], [13].
4
4) Probe orientation and visuospatial ability
Orientation fluctuates in delirium; dementia has more stable orientation deficits. Simple clock-drawing or intersecting pentagons may be disproportionately impaired in delirium [13].
5
5) Screen for neuropsychiatric profile
Delirium: lability, perceptual disturbance, psychomotor change; Dementia: apathy/indifference with more sustained mood changes [14]. Hypoactive delirium may present as quiet confusion [11].
6
6) Apply a validated tool
Use CAM/CAM-ICU/4AT (if available) and consider DRS-R-98 for severity/phenomenology, which performs in dementia cohorts [8], [6], [9].
7
7) Initiate reversible-cause workup and prevention
Address pain, infection, hypoxia, medications (anticholinergics, benzodiazepines), dehydration, metabolic derangements; mobilize and reorient early [6], [10].
Delirium vs Dementia: Bedside Features and Tests
Prioritize elements with the highest discriminative value in DSD.
Course and Fluctuation
Delirium: acute (hours–days), fluctuating attention/awareness [6], [7]
Dementia: chronic (months–years), gradual decline; minimal fluctuation day-to-day [6], [7]
Subsyndromal delirium exists—maintain vigilance in palliative/older adults [11]
Arousal and Consciousness
Delirium: altered arousal (hyper/hypoactive, mixed) [3]
Dementia: arousal typically preserved until late; daytime somnolence suggests delirium or comorbidity [3]
Attention and Vigilance (Core Tests)
Months backward; digit span; serial 7s/3s (inattention → delirium) [1], [2]
Simple vigilance (A-letter tapping) distinguishes delirium even with dementia [12], [13]
Errors that fluctuate across the day favor delirium [6]
Cognitive/Neuropsychiatric Profile
Delirium: affective lability, hallucinations, delusions, psychomotor change [14]
Dementia: apathy, indifference, more sustained mood disturbance [14]
Visuospatial deficits can be disproportionately impaired in delirium [13]
Diagnostic Frameworks
DSM/ICD are diagnostic gold standards in research; adapt clinically with CAM/CAM-ICU/4AT [6]
DRS-R-98 characterizes severity and is informative in dementia cohorts [8]
Recognition of DSD requires establishing baseline cognition from informants [9], [10]
Common Pitfalls
Mislabeling hypoactive delirium as progression of dementia [11], [6]
Relying on orientation alone—attention is more discriminative [1], [2]
Ignoring medication/toxin review (anticholinergics, sedatives) [6]
Under-testing vigilance/visuospatial ability that separate delirium from dementia [13]
References
Source material
Primary literature that informs this article.
The Diagnosis of Delirium Superimposed on Dementia
www.sciencedirect.com
The Diagnosis of Delirium Superimposed on Dementia
pmc.ncbi.nlm.nih.gov
Attention, arousal and other rapid bedside screening ...
academic.oup.com
Long-term clinical outcomes of delirium after hospital discharge
academic.oup.com
Delirium is a strong risk factor for dementia in the oldest-old
academic.oup.com
Delirium diagnosis, screening and management
journals.lww.com
Patient education: Delirium (Beyond the Basics) - UpToDate
www.uptodate.com
Performance of the Delirium Rating Scale-Revised-98 ...
www.sciencedirect.com
Recognition of Delirium Superimposed on Dementia
pmc.ncbi.nlm.nih.gov
Identifying Delirium In Persons With Moderate Or Severe ...
pmc.ncbi.nlm.nih.gov
Delirium Diagnostic and Classification Challenges in ...
www.sciencedirect.com
Comparison of cognitive and neuropsychiatric profiles in ...
bmjopen.bmj.com
Comparison of novel tools with traditional cognitive tests in ...
pubmed.ncbi.nlm.nih.gov
Comparison of cognitive and neuropsychiatric profiles in ...
bmjopen.bmj.com