The cingulate island sign (CIS) on 18F-?uorodeoxyglucose 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).

Diagnostic value

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).

Examination Method

They 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 signi?cant 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 signi?cant accuracy for differentiating between AD and DLB. A larger study is needed to replicate these findings.

FDG PET- and IMP SPECT

Both the FDG PET- and IMP SPECT-derived CIS ratios are useful for differentiating between AD and DLB. The FDG-PET-derived CIS ratio is more useful than the IMP SPECT-derived CIS ratio for differential diagnosis in patients with MCI.

The weakest point of this study is the small sample size, although the results reached the statistically significant. A larger sample study is needed. The second weakest point is that a definite diagnosis based on pathological evaluation is lacking.

Further study, adding more cases, and involving comparisons with other modalities and an investigation of the associations between the CIS ratio and clinical or pathological findings, is needed for replication.