Cerebellar Amyloid-β Plaques: How Frequent Are They, and Do They Influence 18F-Florbetaben SUV Ratios?

SUV ratios (SUVRs) are used for relative quantification of F-18-florbetaben scans. The cerebellar cortex can be used as a reference region for quantification. However, cerebellar amyloid-beta (A beta) plaques may be present in Alzheimer disease (AD). The aim of this study was to assess the influence of A beta pathology, including neuritic plaques, diffuse plaques, and vascular deposits, in F-18-florbetaben SUVR when cerebellum is used as the reference. Methods: Using immunohistochemistry to demonstrate A beta plaques and vascular deposits, and using the Bielschowsky method to demonstrate neuritic plaques, we performed a neuropathologic assessment of the frontal, occipital, anterior cingulate, and posterior cingulate cerebral cortices and the cerebellar cortex of 87 end-of-life patients (64 with AD, 14 with other types of dementia, and 9 nondemented aged volunteers; mean age +/- SD, 80.4 +/- 10.2 y) who had undergone F-18-florbetaben PET before death. The lesions were rated as absent (none or sparse) or present (moderate or frequent). Mean cortical SUVRs were compared among cases with different cerebellar A beta loads. Results: None of the 83 evaluable cerebellar samples showed frequent diffuse A beta or neuritic plaques; 8 samples showed frequent vascular A beta deposits. Diffuse A beta plaques were rated as absent in 78 samples (94%) and present in 5 samples (6%). Vascular A beta was rated as absent in 62 samples (74.7%) and present in 21 samples (25.3%). No significant differences in cerebellar SUVs were found among cases with different amounts or types of A beta deposits in the cerebral cortex. Both diffuse and neuritic plaques were found in the cerebral cortex of 26-44 cases. No significant SUVR differences were found between these brains with different cerebellar A beta loads. Conclusion: The effect of cerebellar plaques on cortical F-18-florbetaben SUVRs appears to be negligible even in advanced stages of AD with a higher cerebellar A beta load.