PET and SPECT functional imaging in Parkinson's disease.

Neuroimaging studies of the dopaminergic system with positron emission tomography and single photon emission computed tomography radioligands are useful in the assessment of neuronal degeneration in Parkinson's disease. Abnormalities can be identified early in the disease process and used to monitor progression as well as the effect of treatment. Studies of dopamine receptors and brain metabolism can help identify those patients who have other Parkinsonian syndromes, such as multiple system atrophy, progressive sopranuclear palsy or diffuse Lewy body dementia. The current available diagnostic criteria for these disorders rely solely on the presence of signs and symptoms that may require months or years to become fully clinically manifest. Conversely, the use of neuroimaging techniques can significantly shorten the diagnostic process and prove a useful means to the neurologist in those cases presenting with uncertain clinical diagnosis.