Patterns of regional cerebellar atrophy in genetic frontotemporal dementia

• Different pattern of cerebellar atrophy in the major genetic forms of FTD
• Involvement of the lobule VIIa-Crus I in C9orf72 carriers, related to cognition
• MAPT carriers show vermal involvement, linked to emotional processing
• GRN carriers show relative sparing of the cerebellum

BackgroundFrontotemporal dementia (FTD) is a heterogeneous neurodegenerative disorder with a strong genetic component. The cerebellum has not traditionally been felt to be involved in FTD but recent research has suggested a potential role.MethodsWe investigated the volumetry of the cerebellum and its subregions in a cohort of 44 patients with genetic FTD (20 MAPT, 7 GRN, and 17 C9orf72 mutation carriers) compared with 18 cognitively normal controls. All groups were matched for age and gender. On volumetric T1-weighted magnetic resonance brain images we used an atlas propagation and label fusion strategy of the Diedrichsen cerebellar atlas to automatically extract subregions including the cerebellar lobules, the vermis and the deep nuclei.ResultsThe global cerebellar volume was significantly smaller in C9orf72 carriers (mean (SD): 99989 (8939) mm3) compared with controls (108136 (7407) mm3). However, no significant differences were seen in the MAPT and GRN carriers compared with controls (104191 (6491) mm3 and 107883 (6205) mm3 respectively). Investigating the individual subregions, C9orf72 carriers had a significantly lower volume than controls in lobule VIIa-Crus I (15% smaller, p < 0.0005), whilst MAPT mutation carriers had a significantly lower vermal volume (10% smaller, p = 0.001) than controls. All cerebellar subregion volumes were preserved in GRN carriers compared with controls.ConclusionThere appears to be a differential pattern of cerebellar atrophy in the major genetic forms of FTD, being relatively spared in GRN, localized to the lobule VIIa-Crus I in the superior-posterior region of the cerebellum in C9orf72, the area connected via the thalamus to the prefrontal cortex and involved in cognitive function, and localized to the vermis in MAPT, the ‘limbic cerebellum’ involved in emotional processing.