Abstract: We included one study that was applicable to our first objective (A). It reported data on 22 participants who met consensus clinical criteria for DLB or National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria for Alzheimer's disease, or both (a two-gate design with alternative diagnosis controls). The index test was SPECT scanning using the ligand 123I-FP-CIT. We considered the study to be at high risk of bias in the participant selection and index test domains (QUADAS-2). 123I-FP-CIT SPECT analysed semiquantitatively had a sensitivity of 1.00 (95% confidence interval (CI) 0.66 to 1.00) and a specificity of 0.92 (95% CI 0.64 to 1.00) for the diagnosis of DLB (n = 22, 1 study). Analysed visually, the sensitivity was 0.86 (95% CI 0.42 to 1.00) and the specificity was 0.83 (95% CI 0.52 to 0.98) (n = 19, 1 study). We considered that the study also provided the best available data to address our second objective (B). At baseline, 15 participants were clinically suspected of having DLB. In this group, 123I-FP-CIT SPECT scanning analysed semiquantitatively had a sensitivity of 1.00 (95% CI 0.63 to 1.00) and a specificity of 1.00 (95% CI 0.59 to 1.00) for the diagnosis of DLB (n = 15, 1 study). Analysed visually, accuracy in this group was lower with a sensitivity of 0.83 (95% CI 0.36 to 1.00) and a specificity of 0.71 (95% CI 0.29 to 0.96) (n = 13, 1 study). Only one study has used a neuropathological reference standard to assess the accuracy of DAT imaging for the diagnosis of DLB. The small size of the included study means that sensitivity and specificity estimates are imprecise. However, data from this study suggest that DAT imaging is more accurate than clinical diagnosis. Clinical diagnosis is therefore unsuitable to use as a reference standard for assessing the accuracy of DAT imaging. No studies using a neuropathological reference standard have directly addressed the common clinical scenario where the use of DAT imaging is considered as a diagnostic test in a person with possible DLB, or assessed the accuracy of DAT imaging in people with mild dementia. However, the data from the included study suggest that, where there is moderately severe dementia and a strong pre-existing suspicion of DLB (probable DLB), then a normal (123)I-FP-CIT SPECT scan may be an accurate means of excluding the diagnosis. Semiquantitative ratings of 123I-FP-CIT SPECT scans appeared to be more accurate than visual ratings in all analyses.

Plain-language summary: We found only one study of 22 participants to include in the review. The participants had been selected for the study because they had been diagnosed clinically with DLB or AD. This method of recruiting participants tends to exaggerate the accuracy of a test. The participants in the study had moderately severe dementia when they had the DAT imaging. Overall, the DAT imaging correctly classified 100% of the participants who had DLB and 92% of the participants who did not have DLB at postmortem. When we looked at only the 15 participants whom the doctors thought had DLB at the start of the study, then the DAT imaging correctly classified 100% of the participants who had DLB and 100% of the participants who did not have DLB at postmortem. The small size of the included study meant that we could not be very confident in these estimates of accuracy, and it is still possible that the test is considerably less accurate than this would suggest. We can conclude that DAT imaging is a promising test for diagnosing DLB, but it is important to note that we did not find any studies of participants in whom diagnosis may be more difficult, such as those with only mild dementia or those who have only one symptom to raise a suspicion of DLB.