Dopamine transporter SPECT imaging in Parkinson’s disease and parkinsonian disorders

Abstract

The dopamine transporter (DAT) imaging provides an objective tool for the assessment of dopaminergic function of presynaptic terminals which is valuable for the differential diagnosis of parkinsonian disorders related to a striatal dopaminergic deficiency from movement disorders not related a striatal dopaminergic deficiency. DAT imaging with single-photon emission computed tomography (SPECT) can be used to confirm or exclude a diagnosis of dopamine deficient parkinsonism in cases where the diagnosis is unclear. It can also detect the dopaminergic dysfunction in presymptomatic subjects at risk for Parkinson’s disease (PD) since the reduced radiotracer binding to DATs in striatum is already present in the prodromal stage of PD. This review covers the rationale of using DAT SPECT imaging in the diagnosis of PD and other parkinsonian disorders, specifically focusing on the practical aspects of imaging and routine clinical indications.

Keywords: 123I-ioflupane; Dopamine transporter; SPECT; parkinsonian disorders; Parkinson’s disease; parkinsonian disorders.

Figure 1

Axial 123I-ioflupane DAT SPECT images of three different patients with parkinsonism. (a) Striatal radiotracer uptake is visually symmetrical and normal. The background activity is low. Both striata have comma shape and sharp borders. The findings of the quantitative analysis were in normal ranges. These findings exclude the presence of a striatal dopaminergic deficiency. (b) Radiotracer uptake in putamen is bilaterally decreased and background activity is slightly increased. Both striatal structures took an oval appearance. Specific binding ratios calculated from both putamens were significantly lower than the patient’s age group. The asymmetry index was 25%. Specific binding ratios calculated from the caudate nuclei were also lower than the mean values determined for the patient’s age group, but this difference was not statistically significant (within the 95% confidence interval). These findings indicate a moderate nigrostriatal dopaminergic neuron loss and the pattern of involvement may be consistent with early-stage PD. (c) Striatal radiotracer uptake is decreased and background activity is increased significantly. Specific binding ratios calculated from both putamens and caudate nuclei are significantly lower than the patient’s age group. These findings indicate a severe degree of nigrostriatal dopaminergic neuron loss and the pattern of involvement may be consistent with late-stage PD.

Figure 2

Axial 123I-ioflupane DAT SPECT and brain 18F-FDG PET images of a patient with suspected neurodegenerative parkinsonism. (a) In the 123I-ioflupane DAT SPECT examination radiotracer uptake in basal ganglia is bilaterally decreased and background activity is slightly increased. Both striatal structures took an oval appearance. Specific binding ratios calculated from both putamens and caudate nuclei were significantly lower than the patient’s age group. The decrease in uptake was more prominent in left basal ganglion and asymmetry indices were 10% and 37% for putamen and caudate nucleus, respectively. (b) The axial brain 18F-FDG PET and T1-weighted MR images which were simultaneously acquired on a hybrid PET-MR camera showed bilateral relatively increased putaminal glucose metabolism and normal findings in the cerebral cortex which is defined as a metabolic marker for PD on brain 18F-FDG PET [46]. MR examination did not show a specific pathological change. Taken together, these findings supported the diagnosis of PD in this patient.

Figure 3

Axial 123I-ioflupane DAT SPECT and planar cardiac 123I-MIBG images of a patient with suspected neurodegenerative parkinsonism. (a) In the 123I-ioflupane DAT SPECT examination radiotracer uptake in basal ganglia is bilaterally decreased and background activity is slightly increased. Both striatal structures took an oval appearance. Specific binding ratios calculated from both putamens and caudate nuclei were significantly lower than the patient’s age group. The decrease in uptake was more prominent in left basal ganglion and asymmetry indices were 13% and 10% for putamen and caudate nucleus, respectively. The patient had clinical findings of parkinsonism and autonomic dysfunction and the presumed diagnosis was PD or MSA. Although DAT SPECT findings verified the presence of a striatal dopaminergic neurodegeneration, it was not adequate for making a differential diagnosis between PD and MSA. Therefore, a cardiac 123I-MIBG examination was requested. (b) The planar cardiac 123I-MIBG image displays normal radiotracer uptake in the left ventricle. Since cardiac 123I-MIBG uptake is expected to be decreased in PD and normal in MSA, these findings supported the diagnosis of MSA in this patient [12].