Cortical diffusivity associates with early neuronal damage

Abstract

AbstractBackgroundDiffusion weighted imaging can provide a marker a microstructural damage which cannot be detected by conventional structural MRI. Changes in cortical diffusivity may be a value marker of neuronal breakdown, which predates macrostructural damage. We aimed to evaluate the efficacy of cortical diffusivity in predicting the extent of metabolic changes in different stages of Alzheimer’s disease progression.Method90 participants diagnosed with mild to moderate Alzheimer’s disease were recruited at Imperial College London. A median split was conducted to categorise participants into ‘Early’ (MMSE ≥ 25, n = 42) and ‘Late’ stage of AD groups (MMSE < 25, n = 48) to reflect different stages of disease progression. All participants underwent [18F]fluorodeoxyglucose imaging with arterial input, t1‐weighted MRI images and diffusion weighted images were also acquired. Spectral analysis was conducted to calculate the cerebral metabolic rate of glucose (CMRglc). CMRglc and mean diffusivity maps were spatially normalised to MNI space and individualised grey matter object maps were created for all participants. Linear regression was conducted between CMRglc and mean diffusivity maps. Mean diffusivity and CMRglc values within the temporal lobe were extracted to confirm voxelwise results.ResultIn this cohort, voxel‐wise statistics revealed a significant relationship between cortical diffusivity and reduced CMRglc, particularly in our ‘early’ stage AD group. Most notable correlations were located within temporal lobe regions. Regional analysis revealed that increased temporal lobe mean diffusivity was strongly correlated with decreased CMRglc in ‘early’ AD participants (r=‐0.525, p<0.001, 95% CI: ‐0.263 to ‐0.715). We found evidence of a weaker correlation in the ‘late’ AD group between increased diffusivity and CMRglc reductions within the temporal lobe (r=‐0.322, p=0.026, 95% CI: ‐0.042 to ‐0.555).ConclusionCortical mean diffusivity is a valuable predictor of early neuronal damage measured by cerebral glucose metabolism in Alzheimer’s disease. This association was strongest in earlier stages of the disease trajectory, as such, we establish that cortical mean diffusivity as an early biomarker in Alzheimer’s disease which reflects early changes in tissue integrity and cell/organelle breakdown.