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West London NHS Trust > Patients and carers > Mental and physical health conditions > Dementia > Diagnosis of dementia

Diagnosis of dementia

There is not a single test for dementia, although blood tests and brain scans can rule out other reasons for changes in a person’s behaviour. There are conditions that have similar symptoms to dementia including head injuries, brain tumours, certain infections and drugs, alcohol abuse, and thyroid or vitamin deficiencies.
Diagnosis is made by assesing symptoms using questionnaires that test a person ability to remember facts and draw simple diagrams.
There are different types of dementia, and diagnosis will establish which type a person has:

  • Alzheimer’s Disease: small clumps of protein, known as plaques, begin to develop around brain cells and this disrupts the normal workings of the brain.
  • Vascular dementia: blood circulation problems result in parts of the brain not receiving enough blood or oxygen.
  • Dementia with Lewy bodies: abnormal structures, known as Lewy bodies, develop inside the brain.
  • Frontotemporal dementia: two parts of the brain begin to shrink. Unlike other types of dementia, it usually develops in people under 65. It is much rarer than other types of dementia.