dopaminergic degeneration in early stage Parkinson's disease

123 I)β-CIT binding; and to determine the sample size and frequency of SPECT imaging required to demonstrate a significant effect of a putative neuroprotective agent. Methods: A group of 50 early stage Parkinson's disease patients was examined. Two SPECT imaging series were obtained, 12 months apart. The mean annual change in the ratio of specific to non-specific ( 123 I)β-CIT binding to the striatum, putamen, and caudate nucleus was used as the outcome measure. Results: A decrease in ( 123 I)β-CIT binding ratios between the two images was found in all regions of interest. The average decrease in ( 123 I)β-CIT binding ratios was about 8% in the whole striatum, 8% in the putaminal region, and 4% in the caudate region. Comparison of scans done in nine patients under two different conditions—in the off state and while on drug treatment—showed no significant alterations in the expression of striatal dopamine transporters as measured using ( 123 I)β-CIT SPECT. Power analysis indicated that to detect a significant (p < 0.05) effect of a neuroprotective agent with 0.80 power and 30% of predicted protection within two years, 216 patients are required in each group when the effects are measured in the whole putamen. Conclusions: (