The characteristics of patients with AD and DLB who show the false positive or false negative of Cingulate Island Sign in rCBF SPECT examination

Objectives: The cingulate island sign (CIS) is commonly used for differentiating Lewy body dementia (DLB) from Alzheimer disease (AD). The Cingulate Island Sign score (CIScore) is useful parameter, which is derived from CIS, calculated based on the Z score of occipital lobe and posterior cingulate gyrus on rCBF SPECT. Although the diagnostic ability of the CIS is excellent, both false positive and false negative cases are sometimes experienced. The study was done to clarify the characteristics of cases who show false positive and false negative on rCBF SPECT.

Methods: The subjects were 19 cases of Lewy body dementia (DLB) and 60 Alzheimer disease (AD). All rCBF SPECT data were analyzed and CIScore were calculated for differentiating DLB from AD respectively. The best cut-off threshold of CIScore in the differentiation between DLB and AD was 0.281. The diagnostic ability by CIScore were calculated. In addition, the characteristics of false-positive cases and false negative cases were analyzed such as age, gender and MMSE.

Results: Of sixty AD cases, 51 were true negative and 9 were false positive. In DLB, fifteen of 19 were true positive and 4 were false negative. The diagnostic ability, namely, Sensitivity, Specificity, Positive predictive value, Negative predictive value and Accuracy (ACC) were 79%,85%,63%,93% and 84% respectively. The average of MMSE in AD was 20.2 in the true negative group and 23.7 in the false positive group, showing a higher tendency in the false positive group. The mean age of false negative cases is older than true positive cases (83.4 vs. 74.7).

Conclusions: The CIScore in DLB tended to be higher in elderly people, therefore, it is necessary to take into patient's age in differentiating from AD. In AD, the CIScore tended to be lower values when MMSE is higher. Therefore, MMSE should be also considered in the differential diagnosis.