Screening investigations in dementia

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).

Reference:

• (1) NICE (November 2006). Dementia guideline
• (2) Royal College of Psychiatrists 2005. Forgetful but not forgotten: assessment and aspects of treatment of people with dementia by a specialist old age psychiatry service