Investigations

There are no specific tests for the diagnosis of Alzheimer's disease. The principle is to rule out the differential diagnoses, and to diagnose Alzheimer's by exclusion.

• FBC – anaemia and infection
• Urea and electrolytes; creatinine; glucose – to rule out diabetes; hyponatraemia – in case of renal failure
• clotting, LFTs – for liver function
• B12, folate – for vitamin deficiency
• TSH, T4 – for myxoedema
• ESR – for vasculitis
• ECG – for arrhythmias
• CXR – for malignancy and infection
• urinanalysis – for sepsis.

Routine electroencephalography (to diagnose CJD) and syphilis serology (VRDL) are probably not indicated unless there are unusual features of presentation.

Other possible investigations include:

• CT/MRI scan – check for tumour, hydrocephalus
• Lumbar puncture in cases of chronic meningitis and TB.

In selected cases further investigations may be indicated:

• angiogram
• jejunal biopsy – to exclude Whipple's disease
• cerebral biopsy
• HIV test
• white cell enzymes
• heavy metal and drug screen.

Note that in Alzheimer's disease there is an early degeneration of the limbic system and the temporo-parietal neocortex. Decreased brain activity in these areas may be detected by positron or single photon emission tomography.

Reference:

• (1) Rossor, M. (1993). Alzheimer’s Disease. BMJ: British Medical Journal, 307(6907), 779–782. http://www.jstor.org/stable/29721161
• (2) NICE (June 2018). Dementia: assessment, management and support for people living with dementia and their carers. (Accessed 15 March 2022)