Combined quantitative analysis of the nigro-striata system in multiple system atrophy and Parkinson's disease

Degeneration of the nigrostriatal system occurs in multiple system atrophy (MSA) and Parkinson's disease (PD) via distinct pathological mechanisms. Here, we investigated nigrostriatal degeneration in MSA and PD by combining a newly developed method for evaluating the regional accumulation of dopamine transporter singlephoton emission computed tomography (DAT SPECT) and individual voxel-based morphometry adjusting covariates (iVAC). We recruited 17 MSA patients and 13 PD patients, and compared their clinical and imaging indices. All patients underwent DAT SPECT and head three-dimensional T1-weighted magnetic resonance imaging. We calculated the specific binding ratio (SBR) of the putamen and caudate separately using a region-based method, and evaluated the association between the SBR and iVAC Z-score. SBR values of the putamen and caudate were lower in the PD group than in the MSA group (p < 0.001 for both). The MSA and PD groups had lower SBR values in the putamen than in the caudate (p <0.05 and p <0.001, respectively). We found a negative correlation between the putamen SBR and iVAC Z-score in MSA (p < 0.001, r = -0.775), but such a correlation was not detected in PD. For the caudate, there was no correlation between the SBR and iVAC Z-score in MSA and PD. Our results indicate different mechanisms of reduced uptake of DATs in MSA and PD. The association between the striatal SBR and iVAC Z-score suggests parallel degeneration in the substantia nigra and striatum in MSA.