Cognitive profile of right and left Corticobasal Syndrome

TARGETS A typical aspect of Corticobasal Syndrome (CBS) is asymmetry. Although this feature is considered specific of CBS, its impact on the cognitive manifestations of the disease has only been investigated in case series, and not through formal group studies. Our work aimed at filling this gap in the literature. We expected that differences between left and right patients would emerge for functions that are typically impaired in CBS and typically associated with damage to either the left hemisphere (e.g. language) or the right hemisphere (e.g. visuospatial abilities). MATERIALS AND METHOD We chose to consider lateralization of hypometabolism on brain FDG-PET for classifying patients into left-hemisphere or right-hemisphere CBS (lhCBS, rhCBS). Asymmetry of hypometabolism was rated upon visual inspection of qualitative PET images, and confirmed through statistical within-group paired comparison of left hemisphere and right hemisphere FDG uptake values extracted with Cortex ID Suite, a software for the automated analysis of PET scans. We also verified whether metabolism within each group’s more affected hemisphere (the left for lhCBS, the right for rhCBS) was significantly worse than metabolism within the other group’s more preserved hemisphere (the right for lhCBS, the left for rhCBS), and whether metabolism within both groups’ more affected as well as more preserved hemispheres was overlapping. Participants had to meet standardized criteria for CBS; all phenotypes were included, except primary progressive aphasia which has an obvious lateralization to the left-hemisphere. The cognitive profile was outlined using an extensive battery of standardized neuropsychological tests. RESULTS We enrolled 26 patients with lhCBS and 23 patients with rhCBS, who were matched for socio-demographic characteristics, disease duration and MMSE scores. All neuropsychological measures were largely overlapping in the two groups, with two exceptions: the Digit span was poorer for lhCBS, while visual neglect was more frequent in rhCBS. DISCUSSION This is to our knowledge the first group study comparing the cognitive profile of left and right CBS. Asymmetry was defined based on metabolic imaging, and verified and balanced out between the groups via statistical analysis. The findings are partly surprising, but neuroanatomically plausible. We did not find the predictable major impairment of language in lhCBS and of visuospatial functions in rhCBS, but the major impairment of verbal short-term memory in lhCBS and of spatial attention in rhCBS reflect the fact that the (left and right, respectively) fronto-parietal pathways underpinning these functions are the main loci of neurodegeneration in CBS.