Quantifying the Severity of Parkinson Disease by Use of Dopaminergic Neuroimaging

OBJECTIVE. Parkinson disease is characterized by dopaminergic neuron loss in the substantia nigra pars compacta resulting in presynaptic nigrostriatal dopamine dysfunction. The purpose of this study was to search for an optimal image biomarker to quantify the severity of Parkinson disease by comparing neuromelanin MRI and dopamine transporter SPECT. SUBJECTS AND METHODS. Forty patients with Parkinson disease (Hoehn and Yahr [HY] stage 1, four patients; stage 2, 18 patients; stage 3, eight patients; stage 4, six patients; stage 5, four patients) who underwent neuromelanin MRI and dopamine transporter SPECT were included. The signal-to-noise ratio (SNR) in the substantia nigra pars compacta on neuromelanin MR images and the striatal specific binding ratio (SBR) on dopamine transporter SPECT images were calculated on the basis of the value of each background region. The Mann-Whitney U test was used to test the significance of difference between the early-stage group (HY stages 1 and 2) and the advanced-stage group (HY stages 3-5) for each SNR and SBR. ROC analysis was used to compare intergroup discriminating performance. The correlation of each SNR and SBR with clinical rating scale was assessed. RESULTS. Both SNR and SBR were significantly greater in the early-stage group than in the advanced-stage group (p < 0.05). The ROC AUCs for differentiating the two groups were 0.73 for SNR and 0.89 for SBR. The coefficients of correlation were -0.47 for SNR versus HY stage and -0.67 for SBR versus HY stage. CONCLUSION. Dopaminergic neuroimaging, particularly dopamine transporter SPECT, is a potentially useful imaging biomarker of the severity of Parkinson disease.