Correlation of dopamine transporter imaging with parkinsonian motor handicap: how close is it?

During the past decade, dopamine transporter (DAT) imaging with single photon emission computerized tomography (SPECT) or positron emission tomography (PET) has evolved as an objective in vivo marker of nigrostriatal neuron loss in Parkinson's disease (PD). We investigate the relationship between striatal DAT binding, measured with [(123)I]beta-CIT SPECT, and parkinsonian motor handicap in a sample of 59 PD patients with minimal to severe disability, and review published cross-sectional studies on the correlation between DAT imaging and motor symptoms in PD. Earlier studies as well as the present results show a good correlation between overall striatal DAT binding and global measures of disease severity such as the Hoehn and Yahr scale, the total score on the Unified Parkinson's Disease Rating Scale (UPDRS), and UPDRS activities of daily living, with a progressive decline of DAT binding with increasing disability. A number of studies found a significant inverse correlation of striatal DAT binding with UPDRS motor score. Bradykinesia, posture, gait, and other midline symptoms, such as speech and facial expression, compared with rigidity, seem to be more closely related to striatal DAT binding. By contrast, neither the severity of parkinsonian rest nor of action tremor is related to the degree of dopaminergic denervation as measured by DAT imaging. Motor symptoms in the clinically less affected body side show a closer correlation with striatal DAT binding than do symptoms occurring in the dominantly affected body side. The correlation of putamen and caudate DAT binding with parkinsonian motor handicap seems to be similar. Although there have been limited comparative studies applying [(18)F]fluorodopa PET and DAT imaging in the same group of PD patients, available data suggest that putamen [(18)F]fluorodopa uptake, when compared with striatal DAT binding, may be more closely related to parkinsonian motor handicap.