[PET and SPECT in Parkinson's disease]

Positron emission tomography (PET) with [18F] fluorodopa (FD) assesses nigrostriatal function in vivo. Measurements deriving from FD PET have direct lineal relationship to the nigral cell count in normal ageing and in Parkinson's disease (PD), although in PD the progression of the decline in nigrostriatal dopaminergic function is faster than the controls. The functional anatomy of the movements has been studied using PET and SPECT. The supplementary motor area (SMA) dysfunction is responsible for bradykinesia in Parkinson. The SMA is undereactive in PD during self-generated movements, and this underactivation is reversed by the administration of apomorphine and modulate by the stereotaxic ventral pallidotomy. PET has been used, also, to attempt the differentiation of PD, multiple system atrophy (MSA) and PSP, in vivo, using a number of different radioligands (opiod, dopamine receptor binding). [11C] raclopride PET and [123I] IBF SPECT seemed a promising agents to assessing D2 receptor status in humans. Studies of D2 status have demonstrated normal or increased D2 receptor density in PD and decreased receptor density in PSP and MSA. Using SPECT has been demonstrated marked differences of the DA transporters located on dopaminergic terminals in the striatum in healthy controls and PD patients. Also the correlation of SPECT measures of transporters of DA and motor severity suggests that this may be a useful marker of disease severity in PD.