Dementia guide

Tests for diagnosing dementia

A range of tests and diagnostic procedures is needed to diagnose dementia. The following are the most commonly used.

Assessing mental abilities to diagnose dementia

Questionnaires are often used to help test the mental abilities of the person with symptoms of dementia, and how severe they are. One widely used questionnaire is the mini mental state examination (MMSE). The MMSE assesses a number of different mental abilities, including:

  • short- and long-term memory
  • attention span
  • concentration
  • language and communication skills
  • ability to plan
  • ability to understand instructions

The MMSE is a series of questions, each carrying a score with a maximum of 30 points. Example questions include:

  • memorising a short list of objects and then repeating the list 
  • writing a short sentence that is grammatically correct, such as 'the dog sat on the floor'
  • correctly identifying the current day of the week, followed by the date, the month, the season and the year

The MMSE is not a test to diagnose dementia. However, it is useful for assessing the level of mental impairment that a person with dementia may have. The scoring system works as follows:

  • a score of 28 or above is considered normal
  • a score of 20-27 indicates mild impairment
  • a score of 10-19 indicates moderate impairment
  • a score of less than 10 indicates severe impairment

These scores may be influenced by a person's level of education. For example, someone who cannot read or write very well may score less than 28, but they may not have dementia. Similarly, someone with a higher level of education may achieve a higher score but still have dementia.

Blood tests for dementia

A person with suspected dementia may have blood tests to check their overall level of health and to rule out other conditions that may be responsible for their symptoms, such as thyroid hormones and vitamin B12 levels.

Dementia brain scans

Brain scans are essential for diagnosing dementia. They are needed to check for evidence of other possible problems that could explain a person's symptoms, such as a major stroke or a brain tumour.

Several types of brain scan can be used to help diagnose dementia:

Computerised tomography (CT) scan

A computerised tomography (CT) scan can be used to check for signs of stroke or a brain tumour. However, unlike an MRI scan, a CT scan cannot provide detailed information about the structure of the brain.

Magnetic resonance imaging (MRI)

The National Institute for Health and Clinical Excellence (NICE) recommends using a magnetic resonance imaging (MRI) scan to help confirm a diagnosis of dementia.

An MRI scan can provide detailed information about the blood vessel damage that occurs in vascular dementia, plus any shrinking of the brain (atrophy). In Alzheimer's disease, the whole brain is susceptible to shrinking, whereas in frontotemporal dementia the frontal and temporal lobes are mainly affected by shrinking.

Other scans and procedures

Other types of scan, such as a single photon-emission computed tomography (SPECT) scan or a positron emission tomography (PET) scan, may be recommended if the result of your CT or MRI scan is uncertain. These scans look at how the brain functions and can pick up abnormalities with the blood flow in the brain.

In some cases, an electroencephalogram (EEG) may be taken to record the brain's electrical signals (brain activity).

A lumbar puncture may also be used to check the protein levels in the brain. This procedure involves taking a sample of spinal fluid from the lower back for testing.

Last reviewed: 21/08/2012

Next review due: 21/08/2014


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