Dementia is a brain condition that can affect memory, thinking, mental agility, language,
understanding and emotions. Dementia affects different parts of the brain over time. It can
affect people physically and change the way the brain processes senses such as sight and taste.

PET stands for positron emission tomography. PET scans are imaging tests that are used to
diagnose disease by showing the build-up of radioactive tracers in certain parts of the body. The
radioactive tracers are normally given to a patient by an injection.

FDG stands for fluorodeoxyglucose. FDG is a type of radioactive tracer used in PET scans. FDG is
taken up by the body in the same way as glucose (a type of sugar that is the body’s main source
of energy). FDG-PET brain scans detect and map how the brain is taking up FDG. If uptake is
decreased, it indicates that the brain is not using energy as it should, and possible
neurodegeneration (a loss of neurons in the brain).

There are over 100 kinds of dementia (known as subtypes). The most common are Alzheimer’s
disease, vascular dementia, mixed dementia, dementia with Lewy bodies and frontotemporal
dementia. In Scotland, it is estimated that there are around 90,000 people living with dementia.
However, many people are living with dementia but are undiagnosed.

In order to get a diagnosis of dementia, patients may need to undergo several tests and
assessments. If someone is diagnosed with dementia, doctors will often also try to diagnose the
subtype of dementia that they have. This is important because although the different subtypes
of dementia can have similar symptoms, the treatments that are offered to patients may be
different.

An FDG-PET scan may be useful for some people with dementia, for whom the subtype of
dementia is not clear. However, FDG-PET scans are not readily available in Scotland for people
with dementia. Instead, people in this position are normally offered a different type of scan,
called a SPECT scan. SPECT stands for single-photon emission computed tomography. SPECT
scans are more readily available in Scotland. We have been asked to assess how FDG-PET scans
compare to SPECT scans in this group of patients.

We looked for studies that assessed how accurate FDG-PET scans and SPECT scans are for
people who have a diagnosis of dementia, but in whom it is not clear what subtype of dementia
they have. We also considered other factors such as costs, the experience and perspectives of
patients and their carers, and the practicalities of offering people an FDG-PET scan rather than a
SPECT scan.

We identified several studies on the use of FDG-PET and SPECT scans for people with dementia.
Together these suggest that FDG-PET scans are more accurate, compared with SPECT scans, in
people undergoing assessment for dementia. However, the studies were variable in quality, and
differences between them made it hard to compare the results. More research would allow
more confident conclusions.

In people who have undergone standard assessment for dementia, further investigations
should only be used if clarifying dementia subtype would change the treatment that patients
are offered. Either a SPECT scan or an FDG-PET scan should be considered as a further
investigation for clarifying dementia subtype in people with suspected Alzheimer’s disease or
frontotemporal dementia.

This work will inform the National PET-CT Review Group decision as to whether an FDG-PET
dementia imaging service should be developed as part of a potential PET-CT service expansion
in NHSScotland.