Investigation of dementia is important primarily to exclude reversible causes of cognitive deterioration:
Perform a midstream urine test if delirium is a possibility.
Blood tests:
- FBC, ESR, CRP - anaemia, vasculitis
- T4 and TSH - hypothyroidism
- biochemical screen - hypercalcium or hypocalcaemia
- urea and creatinine - renal failure, dialysis dementia
- glucose
- B12 and folate - vitamin deficiency dementia
- clotting and albumin - liver function
Other possible blood tests (though not routinely requested in primary care) include:
- syphilis serology
- HIV - if in young person
- caeruloplasmin - Wilson's disease
Conduct investigations such as chest X-ray or electrocardiogram (ECG) as determined by clinical presentation.
Other possible specialist investigations include:
- cerebrospinal fluid examination if Creutzfeldt-Jakob disease (CJD) or other forms of rapidly progressive dementia are suspected
- electroencephalography (EEG) - not routinely indicated
- consider in:
- suspected delirium, frontotemporal dementia or CJD
- associated seizure disorder in those with dementia
- brain biopsy
- consider only if a potentially reversible cause is suspected that cannot be diagnosed in any other way
- imaging
- use structural imaging to exclude other cerebral pathologies and help establish the subtype of dementia
- imaging may help to identify treatable causes such as subdural haematoma, normal pressure hydrocephalus, cerebral tumours
- prefer MRI to assist with early diagnosis and detect subcortical vascular changes. However, CT scanning could be used
- priority for CT scan should be given to the following
- atypical presentation
- rapid unexplained deterioration
- unexplained focal neurological signs or symptoms
- history of recent head injury
- urinary incontinence
- gait ataxia early in the illness (2)
- take specialist advice when interpreting scans in people with learning disabilities
- use perfusion hexamethylpropyleneamine oxime (HMPAO) single-photon emission computed tomography (SPECT) to help differentiate Alzheimer's disease, vascular dementia and frontotemporal dementia
- the test is not useful in people with Down's syndrome, who may have SPECT abnormalities resembling Alzheimer's disease throughout life
- if HMPAO SPECT is unavailable, consider 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) as an alternative
- use dopaminergic iodine-123-radiolabelled 2b-carbomethoxy-3b-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (FP-CIT) SPECT to confirm suspected dementia with Lewy bodies (DLB)
Genetic testing – can be offered to patients or to their unaffected relatives if a genetic cause is suspected (1).
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