@article {Provost342, author = {Karine Provost and Amelia Strom and Leonardo Iaccarino and Lauren Edwards and Taylor Mellinger and Julie Pham and Suzanne Baker and Bruce Miller and William Jagust and Renaud La Joie and Gil Rabinovici}, title = {Crossed cerebellar diaschisis on 18F-FDG PET across neurodegenerative diseases: frequency and association with 11C-PIB and 18F-FTP}, volume = {61}, number = {supplement 1}, pages = {342--342}, year = {2020}, publisher = {Society of Nuclear Medicine}, abstract = {342Objectives: Crossed cerebellar diaschisis (CCD) is a common incidental finding on 18F-FDG brain PET studies. This phenomenon has been commonly described in patients with stroke (1-7), but only few case reports or case series have described it in patients with neurodegenerative diseases (8-10). We assessed prevalence of CCD in a large cohort of patients with neurodegenerative diseases and investigated the relationship between CCD and cortical asymmetries of glucose metabolism, amyloid deposition (11C -PIB) and Tau burden (18F-Flortaucipir (FTP)). Methods: We included 76 healthy controls and 197 patients who underwent 18F-FDG PET (30-60 min post-injection) between 2012 and 2019. 117 patients also underwent 11C-PIB (50-70 minutes post-injection) and 18F-FTP (80-100 minutes post-injection) PET. Amyloid-PET status was defined by visual assessment. PET SUVR images were coregistered to corresponding T1-weighted MRIs and FreeSurfer was used to define regions of interest in native space. Indices of asymmetry (IA) were calculated (rightSUVR - leftSUVR / bilateralSUVR) for cerebral cortex, basal ganglia and cerebellar gray matter. Inferior cerebellar gray matter was assessed for 11C-PIB and 18F-FTP to avoid spillover from supratentorial signal. CCD was defined as 18F-FDG cerebellar IA \>3\%, based on the distribution of 18F-FDG cerebellar IA in healthy controls, and confirmed by visual assessment from an experienced nuclear medicine physician. Relationship between 18F-FDG cerebellar IA and 18F-FDG, 11C-PIB and 18F-FTP cortical IA was assessed using Pearson correlation coefficient. Results: CCD was present in 51/197 (26\%) patients. The highest frequency of CCD was observed in patients with clinical diagnoses of corticobasal syndrome (CBS), semantic variant primary progressive aphasia (svPPA) and logopenic variant primary progressive aphasia (lvPPA) (Table 1). 18F-FDG cerebellar IA showed an inverse correlation with both 18F-FDG basal ganglia and cortical IA (ρ= -0.617, ρ= -0.739, both p\<0.001, Figure 1A). Higher cortical 18F-FTP was associated with decreased 18F-FDG in the contralateral cerebellar hemisphere (Figure 1B). This relationship was not found with cortical 11C-PiB (Figure 1C), in particular in amyloid-positive patients. Mediation analyses showed that the relationship between 18F-FTP asymmetry in the cortex and CCD was fully mediated by the relationship between 18F-FTP and 18F-FDG cortical IA (Figure 1D). Conclusions: CCD is present in a significant proportion of patients with neurodegenerative diseases, and is more prevalent in specific phenotypes, especially in typically asymmetric presentations such as CBS, svPPA and lvPPA. The association between CCD on 18F-FDG and cortical 18F-FTP suggests a Tau-related disruption of cortico-ponto-cerebellar pathways in amyloid-positive patients, while amyloid does not seem to play a significant role. Further studies are required to elucidate prognostic value or clinical correlate of CCD. View this table:Table 1. Patient characteristics and prevalence of crossed cerebellar diaschisis (CCD) by diagnosis Table legend: CeIA= cerebellar index of asymmetry, HC = healthy controls, MCI= mild cognitive impairment, tAD = Alzheimer{\textquoteright}s disease dementia (typical), PCA = posterior cortical atrophy, lvPPA = logopenic variant primary progressive aphasia, CBS = corticobasal syndrome, nfvPPA = non-fluent variant primary progressive aphasia, bvFTD = behavioral variant frontotemporal degeneration, svPPA = semantic variant primary progressive aphasia, PSP = progressive supranuclear palsy}, issn = {0161-5505}, URL = {https://jnm.snmjournals.org/content/61/supplement_1/342}, eprint = {https://jnm.snmjournals.org/content}, journal = {Journal of Nuclear Medicine} }