The cingulate island sign in patients with dementia with Lewy bodies or Alzheimer's disease: A direct comparison between 18F-FDG PET and 123I-IMP SPECT.

The cingulate island sign (CIS) on 18F-fluorodeoxyglucose positron emission tomography (FDG PET); i.e., the relative preservation of mid-posterior cingulate cortex metabolism, is a supportive biomarker in the diagnostic criteria for dementia with Lewy bodies (DLB). Information is lacking, however, regarding the diagnostic value of the CIS on FDG PET or 123I-iodoamphetamine single-photon emission computed tomography (IMP SPECT) for differentiating between mild cognitive impairment (MCI) due to Alzheimer's disease (AD) (MCI-AD) and MCI due to DLB (MCI-DLB). We examined the CIS ratio for nine AD patients, nine DLB patients, eight patients with MCI-AD, and nine patients with MCI-DLB using FDG PET and IMP SPECT. The CIS ratio was calculated as the total count density for the mid-posterior cingulate cortex divided by the total count density for the precuneus and cuneus using the stereotactic extraction estimation method. In the dementia groups, receiver operating characteristic analysis of the CIS ratio showed significant accuracy for differentiating between AD and DLB on both FDG PET and IMP SPECT. In the MCI groups, only the FDG PET-derived CIS ratio displayed significant accuracy for differentiating between AD and DLB. A larger study is needed to replicate these findings.