The visual assessment of DaT-SPECT images with uptake in the lower normal semiquantitatively measured range (i.e., 1–2 SDs below the normal mean) were subject to assessment uncertainty (as illustrated in Fig. 1
). In this study, 10 of 171 DaT-SPECT examinations done in parkinsonian patients were judged visually normal and 3 of 37 DaT-SPECT examinations in HCs were judged as pathological. Among the 10 patients (8 PD and 2 APS) with a visually normal DaT-SPECT, all but 1 had semiquantitative uptake ratios in the putamen that were within 2 SDs of the mean uptake in the control group (as presented in Fig. 2
A,B). In this group of 10 patients, the median baseline UPDRS-III score was 25.5 (minimum, 18; maximum, 42), without any statistically significant difference, compared to patients whose DaT-SPECT was judged as pathological (median, 26.0; minimum, 5; maximum, 64; data missing in 2 cases; P
> 0.05). Seven of these patients had more than 2 years of self-reported duration of symptoms and 3 had less than 1 year of self-reported symptoms. Nine of these patients had a clinical follow-up time of 2 to 7 years, whereas 1 PD patient had a follow-up time of less than 1 year (as shown in Table 1
). In 6 of these 10 patients, 1 had a follow-up SPECT after 1 year, 2 had a follow-up SPECT after 1 and 3 years, 1 had follow-up SPECTs after 1, 3, and 5 years, and 2 also had a DaT-SPECT after 8 years. The remaining 4 patients were not followed up with SPECT. The follow-up DaT-SPECTs did not show any progress in 5 cases. In one of the patients, the follow-up DaT-SPECT after 1 year deteriorated, but then, after 3 years, the image was normalized. In 4 PD patients, the DaT-SPECT was visually interpreted as abnormal, but the semiquantitative evaluation showed uptake ratios in the putamen bilaterally that were within the normal range (mean, −2 SDs).
Figure 2. Visually assessed DaT-SPECTs (normal, green circles; pathological, red triangles) plotted against semiquantitative uptake evaluation in the left and right putamen. Each dot represents an individual, indicated by diagnostic entity. (A) Neurocam. (B) Infinia Hawkeye. APS, atypical parkinsonian syndrome (i.e., multiple system atrophy or progressive supranuclear palsy); HC, healthy control; PD, Parkinson's Disease.
Among the 37 HCs, the DaT examination was judged as pathological in 3 subjects (as shown in Table 1). One of these had a follow-up scan after 3 years and 1 had a scan after both 3 and 5 years; all follow-up scans were judged as normal. The third HC only participated at baseline. In all 3 of the HCs with a pathological baseline DaT-SPECT, the semiquantitative uptake ratio was within 2 SDs of the normal mean; 2 had ratios in the lower range and 1 in the higher normal range (as shown in Fig. 2B).
The resulting sensitivity for visual assessment of DaT-SPECT in this group of early-stage parkinsonian patients was 94% and the specificity 92%. This rendered a positive LR (LR+) of 11.75 and a negative LR (LR−) of 0.07. The proportion of false positives was 1.4%, and the proportion of false negatives was 4.8%.