Differentiating Delirium Versus Dementia in Older Adults

Etiology

Although delirium is classified as a single clinical entity, it may be conceptualized as a disturbance in brain function arising from a variety of underlying etiologies. Delirium results from the interaction of intrinsic predisposing factors and acquired precipitating influences; therefore, identifying the underlying etiology in each case is essential, although multiple or difficult-to-detect contributing factors may sometimes be present.[9] The threshold model of deliriogenesis suggests that delirium develops from the interaction between a person’s vulnerability and the severity of a harmful insult. Accordingly, in individuals with high vulnerability, even minor insults may precipitate delirium, whereas in those with lower vulnerability, more substantial insults are typically required (see Table. Common Factors Causing Delirium).[12] As per a recent systematic review, the most common predisposing factors for delirium include advanced age, cognitive impairment or dementia, functional impairment (physical, vision, hearing, or frailty), along with various other chronic neurological, cardiovascular, or psychiatric conditions. Male sex was also found to be one of the predisposing factors for the development of delirium. The most common precipitating factors can be divided into 8 distinct categories: surgical factors, systemic illness or organ dysfunction, metabolic abnormalities, pharmacology, iatrogenic and environmental factors, trauma, biomarkers, and neurotransmitters.[13] 

Table. Common Factors Causing Delirium 

Dementia represents a neurodegenerative process arising from multiple etiologies and is classified under DSM-5 into 13 subtypes, with Alzheimer disease as the most common. Other subtypes include:

• Vascular dementia
• Frontotemporal dementia (Please see StatPearls' companion resource, "Frontotemporal Lobe Dementia," for further information.)
• Lewy body disease (Please see StatPearls' companion resource, "Lewy Body Dementia," for further information.)
• Parkinson disease (Please see StatPearls' companion resource, "Parkinson Disease," for further information.)
• HIV infection–related cognitive impairment
• Huntington disease (Please see StatPearls' companion resource, "Huntington Disease," for further information.)
• Prion disease
• Substance- or medication-induced dementia
• Traumatic brain injury–related dementia
• Dementia due to another medical condition, multiple etiologies, and unspecified causes [8]

Etiologies may be genetic, acquired, or mixed. Pathophysiologic mechanisms vary and include deposition of amyloid plaques and neurofibrillary tangles composed of hyperphosphorylated tau protein in Alzheimer disease, intracellular accumulation of alpha-synuclein in Lewy body dementia, cumulative vascular insults and cerebral infarctions in vascular dementia, and deposition of ubiquitinated TDP-43 and hyperphosphorylated tau proteins in frontotemporal dementia.

Most cases occur sporadically, although genetic contributions, eg, the APOE e4 allele, increase susceptibility in Alzheimer disease. Infectious causes remain rare but include conditions, eg, Creutzfeldt-Jakob disease and HIV-related dementia. Physical trauma, including traumatic brain injury and cerebrovascular accidents, also contributes to disease development.[8] Evidence identifies delirium as an independent risk factor for subsequent dementia.[7][14]

Neuroinflammation plays a role in the pathogenesis of both delirium and dementia, with ongoing research focused on identifying inflammatory biomarkers to improve prediction and prevention strategies. However, this work remains in early stages. A proposed model suggests that individuals with high vulnerability to delirium, driven by neurodegeneration or dysregulated neuroinflammation, may develop delirium when compensatory mechanisms such as cognitive reserve fail to sustain normal neurological function. Delirium onset may accelerate underlying neurodegenerative processes through inflammatory pathways or gene–inflammation interactions. In some cases, delirium may produce direct neuronal injury, with de novo mechanisms contributing to later dementia development.[4]

Epidemiology

The incidence and prevalence of both dementia and delirium increase with age. As per recent epidemiological data, in the United States, over 2.6 million adults aged 65 years and older develop delirium each year. According to a meta-analysis and systematic review, delirium was observed in 23% of adult medical patients in secondary care.[15] As per a recent systematic review, the prevalence of dementia, for which Alzheimer disease is the most common form, was noted to range from 12.9% to 63% in hospitalized adults older than 55. Dementia is estimated to increase from 57.4 million cases globally in 2019 to more than 150 million cases in 2050.[16] Dementia is the seventh leading cause of death and one of the major causes of disability and dependence in older adults globally, according to the World Health Organization (WHO). Alzheimer's disease is the most common type of dementia, followed by vascular and Lewy body dementia.[8] Frontotemporal type is the second most common type of dementia in patients younger than 65 years of age.[8] The prevalence of DSD was noted to range from 22% to 89% of hospitalized and community populations aged 65 and older with dementia.[17]A 2017 prospective cohort study of 1,409 hospitalized adults older than 60 reported a DSD prevalence of 31%. In contrast, a 2021 meta-analysis of 81 studies including 81,536 individuals with dementia found a pooled in-hospital DSD prevalence of 48.9%. However, reported prevalence rates vary widely across studies due to differences in diagnostic methods, symptom overlap between delirium and dementia, and variations in study populations and methodologies, including age, clinical setting, and whether data were collected prospectively or retrospectively.

Based on data from multiple studies, it has been estimated that among hospitalized patients with dementia, about 1 in 2 to 1 in 5 will develop delirium, which corresponds to a 3- to 4-fold increased risk compared with patients without dementia.[5] As per another study, the risk of death in patients with delirium is 2.6-fold higher than that of those without either dementia or delirium.[18] Baseline dementia has been identified as a predictor of persistent delirium, while DSD is linked to accelerated cognitive decline that may persist for more than 5 years, even after controlling for factors, eg, recurrent hospitalization, baseline cognitive status, and preexisting rates of cognitive decline.[1][19]

In adults older than 60, the incidence of postoperative delirium is 10% to 20%. Additionally, a mortality of 7% to 10% has been reported in patients with postoperative delirium at 30 days following surgery compared with 1% in those without delirium.[20] A study assessing nursing staff's knowledge found that only 21% could recognize hypoactive delirium.[21] 

Pathophysiology

Delirium and dementia frequently coexist, creating complex clinical presentations. The pathophysiologic relationship between these conditions remains incompletely understood. Proposed mechanisms include neuroinflammation, oxidative stress mediated by reactive oxygen species, neurotransmitter imbalances, and chronic stress responses, which contribute to shared and overlapping pathways.[9] 

Pathophysiology varies by dementia subtype. Alzheimer disease involves the accumulation of beta-amyloid plaques, neurofibrillary tangles, and hyperphosphorylated tau protein. Aggregates of alpha-synuclein, reported in 1 in 2 to 1 in 5 cases, characterize Lewy body dementia, Parkinson disease, and multiple system atrophy. Corticobasal degeneration, progressive supranuclear palsy, and frontotemporal dementia (Pick disease) fall within tauopathies.[22] Please see StatPearls' companion resource, "Major Neurocognitive Disorder (Dementia)," for further information on dementia pathologies. Delirium pathophysiology remains poorly defined. Multiple neurotransmitter systems, including cholinergic, dopaminergic, GABAergic, and serotonergic pathways, contribute to its development across diverse etiologies.[12]

History and Physical

History and physical examination are the mainstays of diagnosing delirium and dementia (see Table. Distinguishing features between Dementia, Delirium, and Primary Psychosis). Obtaining a history from both patients and family members is essential, especially since patients with altered mental status may not be able to give a detailed history. The first thing to prioritize in a case of a change in mental status is ruling out any life-threatening conditions, eg, hypoxia, ST elevation in case of a myocardial infarction, or hypoglycemia.

Basic laboratory studies, electrocardiogram (ECG), blood glucose, and urinalysis are to be checked. Though urinary tract infection is a common cause of delirium, older adult patients can also have asymptomatic delirium. Physical exam should include looking for bruising or injuries which could indicate accidental falls or, in some cases, abuse and neglect, which clinicians should always be aware of, something that is underrecognized in older adults. Clinicians should also look for any signs of stroke, intracranial hemorrhage, or subclinical seizures, which are rare but potentially life-threatening causes of mental status changes.[2] In addition to ruling out any acute medical concerns, an essential step is to obtain the patient's baseline mental status and the time course of any mental status changes, which usually requires a family member or caregiver to provide collateral information.[2] 

Delirium is categorized into 3 primary psychomotor subtypes: hyperactive, hypoactive, and mixed. Hyperactive delirium presents with agitation, increased psychomotor activity, and heightened arousal. Although clinicians most readily recognize this form, it accounts for less than 10% of cases encountered in the emergency department. Hypoactive delirium represents the most prevalent subtype, comprising approximately 90% of cases. Clinical features include somnolence and psychomotor retardation. Patients often remain quiet and are less likely to attract clinical attention, contributing to frequent underrecognition. This subtype carries the highest mortality risk. The mixed subtype involves fluctuating features of both hyperactive and hypoactive states, with patients alternating between periods of agitation and decreased responsiveness.[2]

Table. Distinguishing Features Between Dementia, Delirium, and Primary Psychosis 

^a An exception is observed in Lewy body dementia, which characteristically presents with notable fluctuations in cognitive function, representing a distinguishing feature from other dementia subtypes.

Evaluation

Delirium, often described as acute brain failure, requires urgent evaluation and prompt identification of underlying causes. In contrast, dementia generally represents an outpatient diagnosis that necessitates a comprehensive and detailed neurocognitive assessment. Both conditions share several overlapping clinical features, which can complicate differentiation; however, the DSM-5 diagnostic criteria help ensure accurate diagnosis.

The DSM-5 requires the following criteria for delirium:

• Disturbance in attention and awareness develops acutely and tends to fluctuate in severity 
• At least 1 additional disturbance in cognition
• Disturbances that are not better explained by preexisting dementia
• Disturbances that do not occur in the context of a severely reduced level of arousal or coma
• Evidence of an underlying organic cause or causes [11]

Additionally, the DSM-5 formulated the following criteria to diagnose dementia:

• A significant cognitive decline from the baseline level of performance in 1 or more cognitive domains. This can be based on the concerns of the patient, the caregiver, or the significant informant, or on cognitive performance on neuropsychological testing.
• The cognitive impairment interferes with the activities of daily living.
• The cognitive decline does not occur exclusively in the context of delirium.
• No other medical or psychiatric condition better explains the cognitive decline.[23][11]

Diagnosis of Delirium

Basic cognitive assessment for patients with cognitive impairment can include checking orientation to time, place, person, and situation. Attention can also be assessed using simple bedside tests, eg, asking the patient to recite the months of the year or days of the week in reverse order, as inattention is a common feature of delirium. Patients with disorganized or psychotic symptoms, such as visual hallucinations or illogical or disorganized thinking, can be considered signs of delirium unless proven otherwise, as primary psychotic disorders are rare to develop at an older age. Delirious patients can also have difficulty maintaining consciousness, which can fluctuate throughout the day.[2]

Diagnostic tools for delirium

Approximately 100 scales are used worldwide to detect and assess the severity of delirium in clinical settings.[24] Some common and well-known scales for detecting delirium include the Memorial Delirium Assessment Scale (MDAS), the 1998 Revised Delirium Rating Scale (DRS-R-98), and the 4 "A"s Test (4AT). The Confusion Assessment Method (CAM) was developed to help nonpsychiatrists easily detect delirium. CAM includes the 4 main features of acute-onset, fluctuating course of symptoms, inattention, and disorganized thinking or altered mentation, and is the most widely used validated scale for diagnosing delirium. The CAM scale is fairly easy for nonspecialists to use and has high sensitivity and specificity (sensitivity: 94%-100%; specificity: 90%-95%).[25] Other versions of CAM have been developed for use in various settings and by different clinicians, including CAM-ICU, CAM-S, 3D-CAM, and the Ultra-Brief Confusion Assessment Method (UB-CAM). Especially in the ICU, the Richmond Agitation-Sedation Scale (RASS), along with the CAM-ICU, can help detect fluctuations in patient alertness.[26] The high specificity of CAM-ICU enables it to rule out delirium, thereby helping to differentiate delirium from dementia.[27]The 3-Minute Diagnostic Assessment (3D-CAM) is a brief assessment comprising 3 orientation items, 4 attention items, 3 symptom probes, and 10 observational items. This assessment has a sensitivity of 95% and specificity of 94% compared with a clinical reference standard in a prospective validation study of hospitalized patients.[28][29] The 4AT is a very brief (<2 mins) delirium screening tool designed for use in general clinical settings. The 4AT comprises 4 components: assessment of alertness; evaluation of orientation using the Abbreviated Mental Test–4; an attention task using the Months Backward test; and determination of acute change or a fluctuating clinical course. The 4AT is widely used due to its ease of use without specialized training.[30] 

The UB-CAM is another excellent tool for a very brief assessment to rule out delirium. The UB-CAM comprises interview-based questions (2-8 items) and observation of 10 elements. The benefit of this scale is that if the first 2 answers are correct, it indicates no delirium and thus no need for further questions. If incorrect, additional items are then used for further evaluation from the 3D-CAM and an observation scale. If a single correct observation is present, delirium is excluded, thereby negating the need for further evaluation.

The Stanford Proxy Test for Delirium (S-PTD) is a delirium assessment tool designed primarily for nurses to complete at the end of their shifts. For delirium detection, S-PTD showed 82.7% sensitivity, 95.3% specificity, 86.1% positive predictive value, and 94.0% negative predictive value compared with a DSM-5-based neuropsychiatric examination.[31] The Delirium Triage Screen is a rapid assessment tool that does not require collateral information and demonstrates high sensitivity, making it well-suited for use as a screening instrument. If positive, the Delirium Triage Screen will need confirmation using CAM or another tool.[2]

Since cognitive impairment is present in both delirium and dementia, clinicians should be wary of making an initial diagnosis of dementia in hospitalized patients undergoing a delirious episode.[1] Once the patient returns to baseline, further cognitive screening assessment can be performed, starting with the Mini-Cog and the Short Portable Mental Status Questionnaire.[32]

Diagnostic studies

For a definitive diagnosis, an examination should be conducted by a trained healthcare professional with expertise in cognitive testing. For delirium, the physician should test the key components of the CAM algorithm and establish an underlying etiology. In addition to a targeted toxic, metabolic, and infectious workup in a case of delirium, neuroimaging may be indicated. In some cases, electroencephalography (EEG) is performed to rule out status epilepticus and could also indicate a diagnosis of delirium. A lumbar puncture is rarely needed when meningoencephalitis is suspected.[33] Inflammation is thought to be a key factor in the pathogenesis of delirium. None of the inflammatory markers has been validated for clinical application in the diagnosis of delirium to date.[32]

On the other hand, once an acute pathology is ruled out, patients with suspected dementia should undergo a thorough evaluation by a neurologist and psychiatrist or neuropsychologist, followed by neurocognitive testing and neuroimaging studies. Neurocognitive testing provides a more accurate diagnosis of dementia subtypes based on the affected domains. Neuroimaging, eg, magnetic resonance imaging (MRI) with neuroquant, positron emission tomography (PET), single-photon emission computed tomography (SPECT), and functional MRI, is sometimes performed to look for patterns of cerebral atrophy, hippocampal volume, and hypometabolic areas. The Dopamine Transporter Scan (DAT) is specifically reserved for Parkinson and Parkinson-plus syndromes. Genetic testing is seldom performed for cases, eg, Huntington disease.[8]

Treatment / Management

Management of delirium centers on identifying and addressing underlying etiologies, reducing predisposing and precipitating factors, and prioritizing nonpharmacologic interventions. Once one or more causes are identified, first-line management includes minimizing or discontinuing anticholinergic and psychoactive medications, reorienting patients, and maintaining a calm, quiet environment.[33][32] Symptom control remains essential, including management of pain, constipation, vomiting, and other distressing conditions. Functional status should be optimized through the use of visual and hearing aids when impairments are present. Ongoing assessment of fall risk and promotion of mobility are critical, as immobilization, particularly with restraints, correlates with increased delirium rates.(B3)

Family presence supports behavioral management and reorientation. Effective interprofessional communication and coordination remain essential throughout care. Identified metabolic abnormalities require prompt correction.[2] For hyperactive delirium, pharmacologic therapy may be considered when verbal deescalation fails. The American Geriatrics Society (AGS) provides clinical practice guidelines for the prevention and management of postoperative delirium.

Dementia management involves both supportive care and pharmacologic treatment. Early and accurate differentiation from delirium remains essential for appropriate management and improved outcomes. In Alzheimer disease, approved pharmacologic options for moderate to severe stages include cholinesterase inhibitors, eg, galantamine, donepezil, and rivastigmine, as well as memantine. Supportive strategies include cognitive training, cognitive stimulation therapy, nutritional optimization, physical activity, and sleep interventions.[8][9][34]

The AGS Beers Criteria identifies "potentially inappropriate medications" for adults older than 65 years. When such medications appear in a patient’s regimen, clinicians should pursue safer alternatives when feasible.[35] Minimizing polypharmacy and reducing both the number and dosage of medications, particularly psychoactive agents, remains a key component of care.[2]

Differential Diagnosis

The differential diagnoses for delirium and dementia include:

• Delirium 
  • Infections: Urinary tract infections, pneumonia, sepsis, meningitis, encephalitis
  • Metabolic disturbances: Hypoglycemia, hyperglycemia, hyponatremia, hypercalcemia, hypoxia, hepatic or renal failure
  • Medications/toxins: Anticholinergics, benzodiazepines, opioids, polypharmacy, alcohol withdrawal
  • CNS disorders: Stroke, traumatic brain injury, epilepsy/postictal state, increased intracranial pressure
  • Systemic illnesses: Decompensated heart failure, malignancies, dehydration, thyroid dysfunction
  • Psychiatric conditions: Acute psychosis, severe depression, mania [10][9][8]
• Dementia
  • Neurodegenerative disorders: Alzheimer’s disease, Lewy body dementia, vascular dementia, frontotemporal dementia, Parkinson’s disease dementia
  • Chronic infections: Neurosyphilis, HIV-associated dementia, prion diseases (eg, Creutzfeldt-Jakob disease)
  • Toxic/metabolic causes: Chronic vitamin B12 deficiency, Wilson disease, normal pressure hydrocephalus, chronic liver/kidney disease
  • Structural brain disorders: Brain tumors, chronic subdural hematomas
  • Autoimmune/inflammatory diseases: Multiple sclerosis, paraneoplastic syndromes, lupus cerebritis
  • Psychiatric conditions: Late-onset schizophrenia, severe depression with cognitive impairment (pseudodementia) [10][9][8]

Prognosis

Besides distinguishing delirium from dementia, identifying DSD is critical as it often leads to prolonged length of hospital stay, accelerated cognitive and functional decline, increased healthcare costs, and ultimately death.[32] For patients with delirium, the prognosis is generally guarded, and duration can vary according to various factors. The prognosis can be significantly affected by nonpharmacological measures, and thus, improved communication among team members and with the family is key.[2]Delirium is preventable in about 30% of cases.[22] With dementia, the prognosis generally involves a slow progression of symptoms. Hospitalized patients who have prolonged delirium are approximately 3 times more likely to die in the following year compared with patients who have a quick resolution or absence of delirium. Consequently, these adverse outcomes reflect reduced functional status and are associated with an increased likelihood of discharge to nursing homes or long-term care facilities following hospitalization.[36]

Complications

Studies have shown up to 2 to 4 times increased mortality in patients who develop delirium in the ICU setting, and up to 1.5-fold increased risk for death in a year following hospitalization in those admitted to general medical, geriatric services, and nursing home residents with comorbidities, eg, stroke and dementia.[33] A high risk of falls or even aggressive behavior in patients with dementia and delirium is present, which can cause harm to themselves or others, and needs to be monitored and prevented. If necessary, pharmacological interventions may need to be instituted.[36]