The 18F-FDG PET Cingulate Island Sign and Comparison to 123I-β-CIT SPECT for Diagnosis of Dementia with Lewy Bodies

Neuroimaging is increasingly used to supplement the clinical diagnosis of dementia with Lewy bodies (DLB) by showing reduced occipital metabolism and perfusion and reduced striatal dopaminergic innervation. We aimed to optimize the interpretation of F-18-FDG PET images for differentiating DLB from Alzheimer disease (AD) and to compare the results with dopamine transporter imaging using I-123-beta-carbomethoxy-3 beta-(4-iodophenyl)-tropane (123I-beta-CIT) SPECT. Methods: Fourteen subjects with a clinical diagnosis of DLB and 10 with AD underwent both F-18-FDG PET and I-123-beta-CIT SPECT. Four DLB and 1 AD diagnoses were subsequently confirmed at autopsy. Diagnostic accuracy was calculated for visual interpretation by 3 readers of standard 3-plane and stereotactic surface projection F-18-FDG PET images, receiver-operating-characteristic analysis of regional F-18-FDG uptake, and a cutoff value for the striatal-to-occipital binding ratio of beta-CIT defined by receiver-operating-characteristic analysis. Results: Visual interpretation of 3-plane F-18-FDG PET images had a sensitivity of 83% and specificity of 93% for DLB, slightly higher than the results with the stereotactic surface projection images. Regionally, hypometabolism in the lateral occipital cortex had the highest sensitivity (88%), but relative preservation of the mid or posterior cingulate gyrus ( cingulate island sign) had the highest specificity (100%). Region-of-interest analysis revealed that occipital hypometabolism and relative preservation of the posterior cingulate both had a sensitivity of 77% and specificity of 80%. beta-CIT achieved 100% accuracy and greater effect size than did F-18-FDG PET (Cohen d = 4.1 vs. 1.9). Conclusion: Both F-18-FDG PET and I-123-beta-CIT SPECT appear useful for the diagnosis of DLB, although the latter provides more robust results. The cingulate island sign may enhance the specificity of F-18-FDG PET.