Differentials
Alzheimer's disease
SIGNS / SYMPTOMS
Characterised by memory loss, reduced social and occupational functioning, diminished executive function, speech/motor deficits, personality change, and behavioural/psychological disturbance.
Minimal fluctuations in level of consciousness.
Cognitive examination shows short-term memory loss. Absence of significant motor symptoms early in the disease.
Rapid eye movement sleep behaviour disorder is not typically present.
Concomitant Alzheimer's disease pathology is common in DLB, which can result in an atypical clinical syndrome.[1]
INVESTIGATIONS
Clinical history and examination are the best way to differentiate Alzheimer's disease from DLB.
Neuropsychological testing may be helpful if there is a prominent amnestic syndrome early in the disease.
Structural and functional imaging may also be of benefit.
In Alzheimer's disease, there is decreased perfusion in temporoparietal regions with single-photon emission CT/PET.
Parkinson's disease
SIGNS / SYMPTOMS
Considerable overlap with DLB.
Visual hallucinations, paranoia, and autonomic dysfunction are common features.
Motor symptoms include rigidity, resting tremor, bradykinesia, and postural instability.
Differentiation from Parkinson's disease dementia (PDD) may be complicated and clinically depends on the relationship of timing of dementia to motor symptom onset: DLB is diagnosed if dementia was present at symptom onset or within 1 year of parkinsonism onset; PDD is diagnosed if a patient had a diagnosis of PD for at least 1 year before the onset of dementia.[1]
INVESTIGATIONS
MRI may show more temporal, parietal, and occipital volume loss than Parkinson's disease. Both DLB and Parkinson's disease show less medial temporal volume loss than Alzheimer's disease.[35]
Frontotemporal dementia
SIGNS / SYMPTOMS
Impulsive, socially inappropriate, and emotionally labile behaviour.
Personality change and behavioural disturbance occur early and are prominent features.
Verbal and language skills are blunted.
Apathy and self-neglect are common.
Parkinsonism in frontotemporal dementia is often associated with eye movement abnormalities (e.g., progressive supranuclear palsy) or asymmetric onset with other neurological findings (e.g., corticobasal syndrome).
Onset often in 50s, progressing more rapidly than DLB.
INVESTIGATIONS
CT or brain MRI reveals structural atrophy in the frontal lobes.
PET or single-photon emission CT scanning shows reduced brain activity in the frontal and temporal lobes.
Brain histology may reveal diagnostic findings (e.g., Pick bodies).
Vascular dementia
SIGNS / SYMPTOMS
Deficits include memory loss, emotional lability, and focal neurological deficits consistent with stroke location.
Cardiovascular risk factors may be present.
Further cognitive and functional decline occurs in a stepwise manner.
Subcortical depression and apathy are common.
INVESTIGATIONS
CT or MRI scanning demonstrates areas of past infarction and perivascular ischaemia.
Prion disorders
SIGNS / SYMPTOMS
May present with rapidly progressive dementia, associated with myoclonus and gait disorder and occasionally visuospatial impairment.
INVESTIGATIONS
Diffusion-weighted MRI may show basal ganglia, thalamic, and cortical changes.
Cerebrospinal fluid analysis is positive for the 14-3-3 protein.
EEG may show characteristic periodic complexes.
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