Clinical validity and reproducibility of a visual rating scale for cingulate island sign in a real-world memory clinic: An FDG-PET/MRI study.

Purpose: Brain [18F]FDG-PET is a supportive biomarker for cognitive impairment in Lewy bodies disease (LBD) showing reduced occipital metabolism and presence of the cingulate island sign (CIS), a relative preservation of posterior cingulate cortex (PCC) metabolism compared with precuneus and cuneus. We assess validation, clinical utility, and reproducibility of a qualitative visual CIS scale in the differential diagnosis with Alzheimer's disease (AD) in a memory clinic setting.

Methods: Sixty-seven patients were studied: 36 LBD, of whom 30 with dementia (DLB) and 6 with mild cognitive impairment (MCI-LB), and 31 AD (20 typical and 11 atypical presentations). They underwent FDG-PET/MRI scans and were followed for at least 24 months. The visual CIS rating scale was scored by a nuclear medicine physician and a neurologist independently. Qualitative CIS scores were validated with ROI-based semiquantitative FDG analysis.

Results: Mean CIS scores were 1.84 ± 1.69 for LBD and 0.9 ± 1.24 for AD (p = 0.001). With a cutoff CIS score ≥2, sensitivity was 0.56, and specificity 0.81 (accuracy 0.67). Positive CIS in patients with AD was due to atypical presentations. Negative CIS in LBD was due to (i) normal FDG-PET in MCI-LB or (ii) marked hypometabolism of both the PCC and cuneus. Visual CIS scores correlated with FDG-uptake (r = 0.45; p < 0.001) and held a high inter-specialists concordance.

Discussion: The visual CIS scale can be successfully scored by different specialists. Lower sensitivity is expected in cases of MCI-LB or dementia due to mixed LBD/AD changes. Specificity may be influenced by the inclusion of atypical AD cases.