Background: Age-related neurodegeneration, sarcopenia, and ectopic fat accumulation are conditions with shared pathways that remain poorly understood. We have measured muscle volume and fat accumulation in masseter and tongue muscle, and aim to explore their association with the total grey matter volume using MRI in older adults recently diagnosed with Alzheimer's disease (AD) and Dementia with Lewy bodies (DLB).
Methods: In this cross-sectional study, people newly diagnosed with mild AD (n=33) and DLB (n=20) underwent structural head MRI. Muscle volume and intramuscular fat (iMAT) of the tongue and masseter were computed using Slice-O-Matic software for segmentation. Total grey volume and hippocampal volumetric segmentation were performed with the FreeSurfer image analysis suite version 6.0. Independent regression models were employed to analyse the associations.
Results: Tongue iMAT was higher and total grey volume lower in DLB compared to AD. In the DLB group, tongue muscle was positively associated with total grey matter volume Est 0.92 (SE 0.24 p-value 0.002), left- Est 0.01 (SE 0.0028 p-value 0,002), and right- Est 0.0088 (SE 0.0027 p-value: 0.005) hippocampal volume. There were no statistically significant results for AD.
Conclusion: Tongue muscle volume was positively associated with hippocampal and total grey volume in DLB. Longitudinal designs are required to explore the extent and significance of this association.