General MedicineTier 1Approach to a presentation

Undifferentiated presentations - confusion

Red flags

Acute onset with fluctuation - delirium, treat as medical emergency until cause found (see delirium note)
Confusion + focal neurology - stroke, mass lesion
Confusion + fever/meningism - CNS infection
Confusion + hypoglycaemia/hypoxia - immediately reversible, check first
Confusion in the context of known dementia with acute behaviour change - superimposed delirium, not progression of baseline

Acute confusion (delirium) - see dedicated delirium note for full differential

Infection, metabolic derangement, drugs, structural lesion, retention/impaction, withdrawal

Chronic/progressive confusion

Dementia (Alzheimer's, vascular, Lewy body, frontotemporal) - insidious onset, stable course day-to-day
Depression ("pseudodementia" - subjective memory complaints often exceed objective deficit, mood symptoms prominent)
Normal pressure hydrocephalus (gait apraxia, urinary incontinence, cognitive decline triad)
Chronic subdural haematoma (esp. elderly, anticoagulated, may lack clear trauma history)
Hypothyroidism, B12 deficiency - reversible causes of cognitive decline

Timeline is the single most important discriminator - acute/fluctuating (delirium) vs insidious/progressive (dementia) vs episodic (depression, TIA)
Collateral history essential - baseline function, rate of change
Medication review, alcohol use, falls/head injury history
Mood, motivation, sleep (depression screen)

FBE, UEC, calcium, TFT, B12/folate, glucose, LFT - reversible dementia screen
CT/MRI brain - structural cause, chronic subdural, NPH, vascular changes, atrophy pattern
Consider syphilis/HIV serology, autoimmune/paraneoplastic screen in atypical/rapid presentations

Establish acute vs chronic first - this determines the entire pathway (delirium workup vs dementia workup)
Treat reversible causes found (B12/folate replacement, thyroxine, stop causative drugs)
Dementia - cholinesterase inhibitors/memantine per subtype and stage, cognitive and functional support, driving/capacity assessment, advance care planning
Depression-related cognitive complaints - treat the depression, reassess cognition after response
NPH - neurosurgical referral for shunting if triad + imaging + response to trial CSF drainage

Superimposed delirium on dementia is easily missed/attributed to "just their dementia getting worse" - always ask about the timeline of the acute change
Depression can mimic dementia convincingly in the elderly ("pseudodementia") - treatable and reversible if recognised
Chronic subdural haematoma can present with confusion alone, without a clear trauma history, especially in anticoagulated elderly patients

"Acute and fluctuating is delirium until proven otherwise; insidious and progressive is dementia until proven otherwise - the timeline drives the whole workup."

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