Differentials
Delirium
SIGNS / SYMPTOMS
Inattention and fluctuating level of consciousness.
Disorientation common.
Reversible causes may be present and should be corrected.
Fluctuating course, worse at night-time.
Fragmentary, fleeting hallucinatory experiences; visual, tactile, or auditory in form.
INVESTIGATIONS
The Confusion Assessment Method (CAM) screening tool is well validated in distinguishing dementia.
Repeated Mini-Mental State Examination or CAM evaluations will show acute fluctuations over time.
Depression
SIGNS / SYMPTOMS
Hallmark features are depressed mood and loss of interest/pleasure in usual activities.
Memory loss is not the predominant feature, although memory complaints are common in older people with depression.
Depression may present acutely.
Negative cognitions, preserved visuo-spatial function, and biological symptoms may help to differentiate.
INVESTIGATIONS
Geriatric Depression Scale (long and short form), Hamilton Depression Scale, and Cornell Scale for Depression in Dementia may help to differentiate.
Limited or no changes on MRI scanning.
Vascular dementia
SIGNS / SYMPTOMS
Deficits include memory loss, difficulty in problem solving, disinhibition, and focal neurological deficits consistent with stroke location.
Cardiovascular risk factors may be present.
Further cognitive and functional decline usually occurs in a stepwise manner.
Subcortical depression and apathy are common.
Clinical history of temporally associated stroke symptoms supports this diagnosis.
Sometimes co-exists with AD (mixed dementia).
INVESTIGATIONS
CT or MRI scanning demonstrates areas of past infarction and perivascular ischaemia.
Dementia with Lewy bodies
SIGNS / SYMPTOMS
Vivid visual hallucinations, Parkinson's features (shuffling gait, bradykinesia, and falls), and cognitive fluctuations are characteristic.
Rapid eye movement sleep disorder may be present.
Progression of disease is more rapid than AD.
INVESTIGATIONS
No reliable or valid differentiating test.
Brain pathology demonstrates the presence of round, eosinophilic, intraneuronal inclusions called Lewy bodies. Neuropathological findings include neurofibrillary tangles, amyloid plaques, and Lewy neurites.
Frontotemporal dementia
SIGNS / SYMPTOMS
Behavioural variant: impulsive, socially inappropriate behaviour; marked apathy or inertia; loss of empathy; hyperorality; marked executive dysfunction.
Personality change and behavioural disturbance occur early and are prominent features.
Language variants may be progressive non-fluent aphasia, semantic dementia (word meaning), or logopenic (impaired word finding and difficulty with repetition).
Onset often at the ages of 50 to 60 years, but may present at a younger age. Progresses more rapidly than AD.
INVESTIGATIONS
CT or brain MRI reveals structural atrophy in the frontal and/or temporal lobes.
Positron emission tomography or single-photon emission CT scanning shows reduced brain activity in the frontal and temporal lobes.
Brain histology may reveal diagnostic findings (such as Pick bodies composed of tau protein, TDP-43 proteinopathy, or FUS proteinopathy).
Parkinson's disease dementia
SIGNS / SYMPTOMS
Features are similar to dementia with Lewy bodies and may include progressive cognitive decline and well-formed visual hallucinations in the context of established Parkinson's disease.
Motor symptoms include rigidity, resting tremor, bradykinesia, and postural instability preceding cognitive symptoms.
INVESTIGATIONS
MRI usually reveals global brain atrophy in people with Parkinson's disease.
Creutzfeld-Jacob disease (CJD)
SIGNS / SYMPTOMS
Rapid decline in cognition or behaviour over several months in sporadic form; longer in variant form.
Prominent psychiatric/behavioural symptoms in variant form (early onset, found mainly in UK and Europe).
Marked impairment in executive functioning. Early neurological signs include startling myoclonus and paraesthesias, progressing to incontinence of urine and faeces, plus loss of speech.
INVESTIGATIONS
Sporadic form: signal hyperintensity often present in the caudate nucleus and putamen on diffusion-weighted and fluid-attenuated inversion-recovery MRI. Cortical ribboning is also a common feature on these imaging sequences.
Pulvinar sign in variant CJD (vCJD) is a common MRI finding.
Tonsillar biopsy may be future diagnostic development in vCJD.
Characteristic electroencephalogram (EEG) findings are triphasic periodic sharp wave complexes seen on repeated EEG testing.
Cerebrospinal fluid 14-3-3 protein assays are recommended to aid in diagnosis when the clinical suspicion is high.
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