[123I]β-CIT SPECT is a useful method for monitoring dopaminergic degeneration in early stage Parkinson's disease

Abstract

Objectives: To examine the validity of [123I]β-CIT SPECT for monitoring the progression of dopaminergic degeneration in Parkinson's disease; to investigate the influence of short term treatment with D2 receptor agonists on striatal [123I]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 [123I]β-CIT binding to the striatum, putamen, and caudate nucleus was used as the outcome measure. Results: A decrease in [123I]β-CIT binding ratios between the two images was found in all regions of interest. The average decrease in [123I]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 [123I]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: [123I]β-CIT SPECT seems to be a useful tool to investigate the progression of dopaminergic degeneration in Parkinson's disease and may provide an objective method of measuring the effectiveness of neuroprotective treatments. Short term treatment with a D2 agonist does not have a significant influence on [123I]β-CIT binding to dopamine transporters. If the latter finding is replicated in larger groups of patients, it supports the suitability of [123I]β-CIT SPECT for examining the progression of neurodegeneration in patients being treated with D2 receptor agonists.