SPECT and PET imaging of the dopaminergic system in Parkinson's disease

This paper gives an overview of the clinical importance of SPECT and PET im aging of the dopaminergic system in the differential diagnosis and for the determination of the progression rate of Parkinson's disease (PD). D2 recep tor imaging can help to differentiate multiple system atrophy (MSA) and pro gressive supranuclear palsy (PSP) from PD. In patients treated with neurole ptics it is possible to determine the rate of striatal D2 receptor blockade using this technique. This occupancy rate parallels the occurrence of park insonian side effects. Its measurement helps in the selection of newer atyp ical neuroleptics. which can be used to treat drug-induced psychosis in PD because they do not aggravate parkinsonian symptoms. Imaging of dopaminergi c neurons with [I-123]beta-CIT SPECT or [F-18]DOPA PET is a way to visualiz e and quantify the nigrostriatal dopaminergic lesion in PD. Findings correl ate with clinical rating scales and demonstrate the feasibility of detectin g the preclinical lesion in patients with hemiparkinson or familial PD. [I- 123]beta-CIT SPECT can easily distinguish patients with essential tremor an d patients with ''lower body parkinsonism" due to a subcortical vascular en cephalopathy. MSA and PSP cannot be separated from PD with this method alon e. Longitudinal studies with [I-123]beta-CIT SPECT and [F-18]DOPA PET can q uantify the progression rate in PD. SPECT results from our own group show a low rate of progression in patients with a long duration of disease and a more marked progression rate in patients with shorter disease duration. In the former group regions in the striatum with higher beta-CIT binding at th e time of the first SPECT scan decline raster than regions with lower bindi ng. These findings suggest a curvilinear course of progression which starts at different time points in different striatal regions and which levels of f after several years of disease duration. These findings are in line with data from PET studies and underline the importance of an early start of neu roprotective strategies. Preliminary data from PET and SPECT studies in ear ly PD suggest that dopamine agonists might have a slight neuroprotective ef fect and might slow down the rate of progression of the disease.