Delirium vs dementia vs depression in older adults — CAM, MMSE/MoCA, reversible causes, comprehensive geriatric assessment

1. Definition and clinical relevance

Delirium, dementia, and depression are the three most common causes of cognitive and behavioural change in older adults, and they frequently coexist. Delirium is an acute neuropsychiatric syndrome characterised by fluctuating disturbance in attention, awareness, and cognition, almost always driven by an underlying medical cause. Dementia is a chronic, progressive decline in multiple cognitive domains that impairs daily function and is largely irreversible, though some causes are treatable. Depression in older adults often mimics cognitive impairment (pseudodementia) and is under-recognised because its symptoms overlap with normal ageing and physical illness.

For an Australian intern, distinguishing these three conditions is time-critical: delirium signals an acute medical emergency requiring urgent cause-finding, while missing depression in a cognitively impaired patient leads to avoidable suffering. All three conditions are common in hospital wards, aged care facilities, and general practice, and misdiagnosis drives inappropriate prescribing, prolonged admissions, and preventable functional decline.

2. Key values, thresholds, scoring systems

Confusion Assessment Method (CAM)

The CAM requires features 1 and 2, plus either 3 or 4, for a positive result.

Cognitive screening tools

MoCA is more sensitive than MMSE for mild cognitive impairment and executive dysfunction. MMSE is better validated for tracking moderate-to-severe dementia over time. Neither tool alone diagnoses delirium.

Distinguishing the three Ds

Geriatric Depression Scale (GDS)

A 15-item or 30-item self-report scale validated for older adults. A score of 5 or more on the short form warrants further assessment. The Cornell Scale for Depression in Dementia is preferred when cognitive impairment is already established, as it relies on observed behaviour and carer report rather than self-report.

3. Approach: presentation and differential

History

Older adults frequently present atypically. A single presenting complaint is unusual; the "big four" geriatric syndromes to screen for are immobility, instability (falls), impaired cognition or memory, and incontinence. Collateral history from a family member or carer is essential because patients with delirium or dementia are unreliable historians.

Red flags for delirium:

• Acute change in behaviour or cognition over hours to days
• Known precipitant: infection (UTI, pneumonia, sepsis), medication change, surgery, metabolic disturbance, pain, urinary retention, constipation, or alcohol withdrawal
• Fluctuating alertness, especially worse at night (sundowning)
• Visual hallucinations

Red flags for dementia:

• Gradual memory loss affecting daily function, reported by family
• Word-finding difficulty, getting lost in familiar places
• Personality or behavioural change over months
• History of vascular risk factors (suggesting vascular dementia)

Red flags for depression:

• Social withdrawal, not leaving home without a physical explanation
• Persistent low mood, anhedonia, hopelessness, or guilt
• Reduced appetite and weight loss
• Somatic complaints disproportionate to physical findings
• Cognitive complaints that are worse on formal testing than in daily life (the reverse of dementia)

Examination

Full mental state examination is mandatory. Assess orientation, attention (serial 7s or months of the year backwards), memory, language, and visuospatial function. Neurological examination may reveal focal signs pointing to stroke or space-occupying lesion. Assess for signs of infection, dehydration, pain, urinary retention, and medication toxicity. Gait assessment (Timed Up and Go test) and functional assessment complete the picture.

Differential diagnosis (in order of urgency)

1. Delirium secondary to sepsis (UTI, pneumonia, bacteraemia)
2. Delirium secondary to medication toxicity or withdrawal
3. Delirium secondary to metabolic disturbance (hyponatraemia, hypoglycaemia, hypercalcaemia, uraemia, hepatic encephalopathy)
4. Delirium secondary to intracranial pathology (subdural haematoma, stroke, space-occupying lesion)
5. Delirium secondary to pain, constipation, or urinary retention
6. Dementia (Alzheimer's, vascular, Lewy body, frontotemporal)
7. Depression or pseudodementia
8. Bipolar disorder, late-onset psychosis

4. Investigations

Bedside

• Vital signs including temperature, oxygen saturation, blood glucose (BSL)
• Urinalysis (dipstick and MSU if positive)
• ECG (arrhythmia, QTc prolongation from medications)
• CAM assessment
• Cognitive screening: AMT or MoCA depending on clinical context
• Pain assessment using a validated scale (Abbey Pain Scale if verbal communication is limited)
• Bladder scan for post-void residual volume

Bloods

Note: laboratory reference ranges in older adults may differ from standard adult ranges. Oxygen saturations of 92 to 95% may be physiologically normal in older adults with comorbidities, and this context should inform interpretation.

Imaging

• Non-contrast CT head: first-line for acute confusion, especially if focal neurology, head trauma, anticoagulation, or new-onset seizure. May reveal subdural haematoma, stroke, space-occupying lesion, or cerebral atrophy. Small vessel disease is a common incidental finding but is associated with cognitive impairment and higher delirium risk.
• MRI brain: superior for posterior fossa lesions, early Alzheimer's (temporal horn atrophy), and Lewy body dementia; arrange as an outpatient if CT is unrevealing and dementia workup is ongoing.
• CXR: pneumonia as a delirium precipitant.

5. Management

Delirium: immediate priorities

1. Identify and treat the underlying cause. This is the single most important intervention.
2. Correct reversible precipitants: treat infection, stop or reduce offending medications (anticholinergics, opioids, benzodiazepines, antihistamines), correct metabolic abnormalities, relieve pain, treat urinary retention or constipation.
3. Non-pharmacological measures first: reorient the patient verbally and with environmental cues (clocks, calendars, familiar objects), ensure hearing aids and glasses are in place, maintain a regular sleep-wake cycle, encourage mobility, ensure adequate hydration and nutrition, involve family in care.
4. Avoid physical restraints where possible; they worsen agitation and increase injury risk.
5. Pharmacological sedation is reserved for patients who are a danger to themselves or others, or where distress is severe and non-pharmacological measures have failed. Low-dose haloperidol (0.5 to 1 mg orally or IM in older adults) is commonly used for hyperactive delirium; use the lowest effective dose for the shortest time. Avoid benzodiazepines except in alcohol or benzodiazepine withdrawal delirium. Involve a senior before initiating antipsychotics.
6. Hypoactive delirium is frequently missed; these patients appear quiet and withdrawn but carry the same risk of complications.

Dementia: management principles

• Identify and treat any reversible contributors (hypothyroidism, B12 deficiency, normal pressure hydrocephalus, subdural haematoma, depression).
• Cholinesterase inhibitors (donepezil, rivastigmine, galantamine) are used in mild-to-moderate Alzheimer's disease; initiation is typically by a specialist. Memantine is used in moderate-to-severe disease.
• Address behavioural and psychological symptoms of dementia (BPSD) with non-pharmacological strategies first. If pharmacological treatment is needed, involve a geriatrician or psychiatrist.
• Polypharmacy review using structured tools is essential; many medications worsen cognition in older adults.
• Advance care planning discussions should begin early, while the patient retains capacity.

Depression: management principles

• Psychosocial interventions (structured activity, social engagement, problem-solving therapy) are first-line for mild depression.
• SSRIs are the preferred antidepressant class in older adults (e.g. sertraline 25 to 50 mg daily, titrating slowly). Start low, go slow.
• Avoid tricyclic antidepressants due to anticholinergic effects, orthostatic hypotension, and cardiac toxicity.
• Response to antidepressants may take 6 to 8 weeks; reassess regularly.
• Refer to old-age psychiatry if there is diagnostic uncertainty, psychotic features, suicidality, or treatment resistance.

Comprehensive Geriatric Assessment (CGA)

CGA is a structured, multidisciplinary evaluation covering physical health, functional ability, cognition, mood, medications, social circumstances, and environment. It is the standard of care for frail older adults and should be initiated early in admission. The MDT includes the geriatrician, nursing staff, occupational therapist, physiotherapist, social worker, dietitian, and pharmacist. CGA informs a holistic care plan and discharge planning, and reduces unnecessary readmissions.

6. Australian-specific considerations

Aboriginal and Torres Strait Islander peoples: Cognitive assessment tools including the MMSE and MoCA were developed in predominantly English-speaking, Western-educated populations and may not be culturally valid for Aboriginal and Torres Strait Islander patients. The Kimberley Indigenous Cognitive Assessment (KICA) is a validated alternative for use in remote and rural Indigenous communities. Dementia rates are significantly higher in Aboriginal and Torres Strait Islander peoples and occur at a younger age, often from the fifth decade. Cultural safety requires involving family and community in assessment and care planning, and recognising that cognitive decline may be attributed to spiritual or social causes within the community. The 715 health assessment (annual health check for Aboriginal and Torres Strait Islander peoples) provides a structured opportunity to screen for cognitive decline, depression, and functional impairment in primary care.

Rural and remote considerations: Access to geriatricians, old-age psychiatrists, and neuropsychologists is limited outside major centres. Telehealth consultations are widely available and should be used early. Retrieval may be required for patients with delirium secondary to serious sepsis or intracranial pathology. Cognitive assessment and CGA components can be initiated by the GP or rural generalist while awaiting specialist input.

Aged care and residential facilities: Mandatory reporting obligations apply if there is reasonable suspicion of abuse or neglect of a resident in an aged care facility. Capacity assessment is required before any significant treatment decision; if capacity is impaired, substitute decision-making frameworks (enduring power of attorney, guardianship) apply under state and territory legislation.

Medications and PBS: Cholinesterase inhibitors for Alzheimer's disease are PBS-listed but require specialist initiation. Antidepressants are PBS-listed without restriction. Antipsychotics used for BPSD carry a black-box warning for increased mortality in older adults with dementia; their use should be documented, time-limited, and reviewed regularly.

Clinical pearls

• A positive CAM requires acute onset with fluctuating course plus inattention, and either disorganised thinking or altered consciousness. Hypoactive delirium is easily missed because the patient appears calm.
• The MoCA is more sensitive than the MMSE for detecting mild cognitive impairment and frontal-executive dysfunction; use it when subtle deficits are suspected.
• Depression in older adults often presents with cognitive complaints and psychomotor slowing rather than overt sadness. The Cornell Scale is preferred over self-report tools when dementia is already present.
• Every episode of delirium demands a systematic search for a reversible cause. UTI, medication toxicity, and constipation are among the most common and most treatable precipitants in hospitalised older adults.
• Small vessel disease on CT head is not a benign incidental finding in older adults; it is associated with cognitive impairment, delirium risk, gait instability, and incontinence.
• Anticholinergic and sedating medications are among the most common iatrogenic contributors to delirium and cognitive decline; medication review is a core component of every CGA.

Sources

• AIHW Aboriginal and Torres Strait Islander health reports
• PBS Schedule (Pharmaceutical Benefits Scheme)