The substantia nigra
(the part of the brain affected in Parkinson’s) is very small and cannot be
seen on the type of brain scans that are available at the moment. The two usual
types of scan, CT and MRI, look normal in someone with
Parkinson’s. Such scans are therefore only used when the doctor has a serious
worry that it could be another condition such as a brain tumour, a blockage of the
system that drains the fluid in the brain, or a stroke. As these concerns are rare,
for most people a brain scan is not necessary. Two other kinds of scan, PET
(Positron Emission Tomography) and DAT (Dopamine Active Transport),
which use radioactive labels, are currently being used by researchers, and can
show the loss of dopamine activity, characteristic of Parkinson’s but which can
also be caused by other types of parkinsonism. However, PET and DAT cannot be
reliably used to differentiate the different types of parkinsonism from each
other. The DAT scan, also called SPECT (Single Photon Emission Computed Tomography), has been
developed and is usually used to separate essential tremor (see previous question)
from other kinds of tremulous parkinsonism, in the few cases where the
diagnosis cannot be made using clinical observation and medical history alone.
