Tc-99m TRODAT-1 and I-123 IBZM SPECT in patients with early Parkinson's disease

Background: Tc-99m TRODAT-1 and I-123 IBZM are potential agents for dopamine transporter (DAT) and dopamine receptor (DR) SPECT, respectively. Mainly involving pre-synaptic neurons, Parkinson's disease (PD) could be differentiated from other movement disorders such as essential tremor and secondary parkinsonism using TRODAT-1 and IBZM SPECT. This study further investigates the value of TRODAT/ IBZM-specific uptake ratios (SUR) of striatum (ST) and putamrn (PU) in evaluating early PD. Methods and Materials: A total of 13 subjects (8 H and Y stage 1, 5 stage II and 5 age-matched controls) were studied. Tc-99m TRODAT-1 (925 MBq) and then I-123 IBZM (259 MBq) SPECT were performed separately within a month using a dual-head camera equipped with an ultra-high resolution fan beam collimator (Helix SPX, Elscint). Ratios of SURs of TRODAT-1 vs. IBZM (RSUR) were measured. Results: Significant differences in averaged SUR of TRODAT-1 were found among controls and patients with stages I and II (2.03, 1.69 and 1.27, p<0.01 respectively). The averaged SUR of IBZM, however, was significantly decreased only in the contralateral ST of the stage II patients. There was a significant decrease of RSUR of ST and PU in diseased groups especially in the contralateral side. Notably, less overlap in putaminal RSURs between diseased groups, either ipisilaterally or contralaterally, and controls was found. Conclusion: The function of DR might be preserved in early PD. The better discrimination of diseased groups from controls using putaminal RSUR might be due to up-regulated DR, which provided a clue to differentiating idiopathic PD from other parkinsonism at the early stage