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

Abstract

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 ¹⁸F-FDG PET images for differentiating DLB from Alzheimer disease (AD) and to compare the results with dopamine transporter imaging using ¹²³I-β-carbomethoxy-3ß-(4-iodophenyl)tropane (¹²³I-β-CIT) SPECT. Methods: Fourteen subjects with a clinical diagnosis of DLB and 10 with AD underwent both ¹⁸F-FDG PET and ¹²³I-β-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 ¹⁸F-FDG PET images, receiver-operating-characteristic analysis of regional ¹⁸F-FDG uptake, and a cutoff value for the striatal-to-occipital binding ratio of β-CIT defined by receiver-operating-characteristic analysis. Results: Visual interpretation of 3-plane ¹⁸F-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%. β-CIT achieved 100% accuracy and greater effect size than did ¹⁸F-FDG PET (Cohen d = 4.1 vs. 1.9). Conclusion: Both ¹⁸F-FDG PET and ¹²³I-β-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 ¹⁸F-FDG PET.