Functional Connectivity Change Associated With Apolipoprotein E Allotypes Precedes Structural Connectivity and Neurodegeneration in Cognitive Normal Older Adults Without Cerebral Aβ Deposition

OBJECTIVE

Apolipoprotein E (APOE) gene is known to influence cerebral functional connectivity (FC) in Alzheimer's disease continuum. We investigated association between APOE allotypes and FC, structural connectivity, and cortical thickness in amyloid-PET negative cognitive normal older adults (CN).

METHODS

A total of 188 CN (37 had ε2/ε2 or ε2/ε3 [ε2 group], 113 had ε3/ε3 [ε3 group], and 38 had ε3/ε4 or ε4/ε4 [ε4 group]) were recruited. Voxel-based morphometry and cortical thickness analysis were used to investigate differences in cortical thickness between three APOE allotypes. To investigate integrity of structural connectivity, we analyzed diffusion weighted imaging using fractional anisotropy and mean diffusivity. In terms of FC, differences of FC in default mode network (DMN) among APOE allotypes were measured using functional magnetic resonance imaging.

RESULTS

There were no significant differences in age, sex, education, cerebral beta-amyloid (Aβ) deposition severity, or neuropsychological profiles. No significant differences were found in cortical thickness and structural connectivity among the APOE allotypes. However, FC within the DMN was significantly lower in ε4 and ε2 carriers compared to ε3 homozygotes.

CONCLUSION

This study suggests that both ε4 and ε2 exhibit APOE-associated DMN FC changes before Aβ deposition, structural changes, and neurodegeneration.

Spectrum-sine interpolation framework for DTI processing

Diffusion tensor imaging (DTI) data interpolation is important for DTI processing, which could affect the precision and computational complexity in the process of denoising, filtering, regularization, and DTI registration and fiber tracking. In this paper, we propose a novel DTI interpolation framework named with spectrum-sine (SS) focusing on tensor orientation variation in DTI processing. Compared with the state-of-the-art DTI interpolation method using Euler angles or quaternion to represent the orientation of DTI tensors, this method does not need to convert eigenvectors into Euler angles or quaternions, but interpolates each tensor's unit eigenvector directly. The prominent merit of this tensor interpolation method lies in tensor orientation information preservation, which is different from the existing DTI tensor interpolation methods that interpolating tensor's orientation information in a scalar way. The experimental results from both synthetic and real human brain DTI data demonstrated the proposed SS interpolation scheme not only maintains the advantages of Log-Euclidean and Riemannian interpolation frameworks, such as preserving the tensor's symmetric positive definiteness and the monotonic determinant variation, but also preserve the tensor's anisotropy property which was proposed in the spectral quaternion (SQ) method.

MRI in acute muscle tears in athletes: can quantitative T2 and DTI predict return to play better than visual assessment?

OBJECTIVES

To assess the ability of quantitative T2, diffusion tensor imaging (DTI) and radiologist's scores to detect muscle changes following acute muscle tear in soccer and rugby players. To assess the ability of these parameters to predict return to play times.

METHODS

In this prospective, longitudinal study, 13 male athletes (age 19 to 34 years; mean 25 years) underwent MRI within 1 week of suffering acute muscle tear. Imaging included measurements of T2 and DTI parameters. Images were also assessed using modified Peetrons and British athletics muscle injury classification (BAMIC) scores. Participants returned for a second scan within 1 week of being determined fit to return to play. MRI measurements were compared between visits. Pearson's correlation between visit 1 measurements and return to play times was assessed.

RESULTS

There were significant differences between visits in BAMIC scores (Z = - 2.088; p = 0.037), modified Peetrons (Z = - 2.530; p = 0.011) and quantitative MRI measurements; T2, 13.12 ms (95% CI, 4.82 ms, 21.42 ms; p = 0.01); mean diffusivity (0.22 (0.04, 0.39); p = 0.02) and fractional anisotropy (0.07 (0.01, 0.14); p = 0.03). BAMIC scores showed a significant correlation with return to play time (Rs = 0.64; p = 0.02), but modified Peetrons scores and quantitative parameters did not.

CONCLUSIONS

T2 and DTI measurements in muscle can detect changes due to healing following muscle tear. Although BAMIC scores correlated well with return to play times, in this small study, quantitative MRI values did not, suggesting that T2 and DTI measurements are inferior predictors of return to play time compared with visual scoring.

KEY POINTS

• Muscle changes following acute muscle tear can be measured using T2 and diffusion measurements on MRI. • Measurements of T2 and diffusion using MRI are not as good as a radiologist's visual report at predicting return to play time after acute muscle tear.

Structural MRI outcomes and predictors of disease progression in amyotrophic lateral sclerosis

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Serial diffusion tensor (DT) MRI showed progression of white matter pathology in ALS.

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Early involvement of motor fibers and later spread to extra-motor regions was found.

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DT MRI measures of damage to the motor networks showed consistent worsening.

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These correlated with clinical progression and long-term functional prognosis.

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No significant cortical thinning was detected either at baseline or over time.

Background and aims

Considering the great heterogeneity of amyotrophic lateral sclerosis (ALS), the identification of accurate prognostic predictors is fundamental for both the clinical practice and the design of treatment trials. This study aimed to explore the progression of clinical and structural brain changes in patients with ALS, and to assess magnetic resonance imaging (MRI) measures of brain damage as predictors of subsequent functional decline.

Methods

50 ALS patients underwent clinical evaluations and 3 T MRI scans at regular intervals for a maximum of 2 years (total MRI scans = 164). MRI measures of cortical thickness, as well as diffusion tensor (DT) metrics of microstructural damage along white matter (WM) tracts were obtained. Voxel-wise regression models and longitudinal mixed-effects models were used to test the relationship between clinical decline and baseline and longitudinal MRI features.

Results

The rate of decline of the ALS Functional Rating Scale revised (ALSFRS-r) was significantly associated with the rate of fractional anisotropy (FA) decrease in the body of the corpus callosum (CC). Corticospinal tract (CST) and CC-body alterations had a faster progression in patients with higher baseline ALSFRS-r scores and greater CC-body disruption at baseline. Lower FA of the cerebral peduncle was associated with faster subsequent clinical progression.

Conclusions

In this longitudinal study, we identified a significant association between measures of WM damage of the motor tracts and functional decline in ALS patients. Our data suggest that a multiparametric approach including DT MRI measures of brain damage would provide an optimal method for an accurate stratification of ALS patients into prognostic classes.

White matter alterations in early Parkinson's disease: role of motor symptom lateralization

INTRODUCTION

Parkinson's disease (PD) is a motor disorder that initially presents with unilateral symptoms. Widespread white matter (WM) alterations have been reported since the early stages of the disease. The aim of this study was to investigate WM alterations in right-dominant and left-dominant symptom PD patients (RPD and LPD, respectively) with respect to healthy controls (HC) by diffusion-weighted magnetic resonance imaging (MRI).

METHODS

Thirty-eight subjects participated in this study: 12 RPD (median H&Y [IQR] = 1.5 [1.1-2], median UPDRS III [IQR] = 23 [7.8-25]), 9 LPD (median H&Y [IQR] = 1.5 [1-2.5], median UPDRS III [IQR] = 17 [12-22]), and 17 HC. All the participants were scanned on a 1.5-T MRI scanner. Maps of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were computed for all the subjects. Tract-based spatial statistics (TBSS) was performed for each diffusion parameter, to test WM differences between RPD, LPD, and HC (ANCOVA design). Family-wise error (FWE) correction was performed and p values lower than 0.05 were considered significant.

RESULTS

No significant FA and RD differences were observed between RPD, LPD, and HC. Significantly increased MD and AD were observed in RPD with respect to HC within widespread WM regions, bilaterally. Conversely, no significant WM alterations were detected in LPD.

CONCLUSION

WM integrity was found to be significantly altered in RPD but not in LPD, suggesting that LPD profile may be associated to more favorable prognosis. Since clinical laterality onset may affect the extent of WM integrity changes, it should be taken into account in neuroimaging studies investigating PD.

Functional and structural brain networks in posterior cortical atrophy: A two-centre multiparametric MRI study

This study identified structural and functional brain connectivity alterations in two independent samples of patients along the posterior cortical atrophy (PCA) disease course. Twenty-one PCA patients and 44 controls were recruited from two expert centres. Microstructural damage of white matter (WM) tracts was assessed using probabilistic tractography; resting state (RS) functional connectivity of brain networks was explored using a model free approach; grey matter (GM) atrophy was investigated using voxel-based morphometry. Compared with controls, common patterns of damage across PCA patients included: GM atrophy in the occipital-temporal-parietal regions; diffusion tensor (DT) MRI alterations of the corpus callosum and superior (SLF) and inferior longitudinal fasciculi (ILF) bilaterally; and decreased functional connectivity of the occipital gyri within the visual network and the precuneus and posterior cingulum within the default mode network (DMN). In PCA patients with longer disease duration and greater disease severity, WM damage extended to the cingulum and RS functional connectivity alterations spread within the frontal, dorsal attentive and salience networks. In PCA, reduced DMN functional connectivity was associated with SLF and ILF structural alterations. PCA patients showed distributed WM damage. Altered RS functional connectivity extends with disease worsening from occipital to temporo-parietal and frontostriatal regions, and this is likely to occur through WM connections. Future longitudinal studies are needed to establish trajectories of damage spreading in PCA and whether a combined DT MRI/RS functional MRI approach is promising in monitoring the disease progression.

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PCA patients showed distributed WM damage.

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In PCA, WM damage is associated with longer disease duration ad greater severity.

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In PCA, altered RS functional connectivity extends with disease worsening.

White matter tract alterations in Parkinson's disease patients with punding

OBJECTIVE

To assess brain white matter tract alterations in patients with Parkinson's disease and punding (PD-punding) compared with controls and PD cases without any impulsive-compulsive behaviour.

METHODS

Forty-nine PD patients (21 PD-punding and 28 PD with no impulsive-compulsive behaviours) and 28 controls were consecutively recruited. Clinical, cognitive and psychopathological evaluations were performed. Diffusion tensor MRI metrics of the main white matter tracts were assessed using a tractography approach.

RESULTS

Compared with controls, both PD groups showed white matter microstructural alterations of the left pedunculopontine tract and splenium of the corpus callosum. PD-punding patients showed a further damage to the right pedunculopontine tract and uncinate fasciculus, genu of the corpus callosum, and left parahippocampal tract relative to controls. When adjusting for depression and/or apathy severity, a greater damage of the genu of the corpus callosum and the left pedunculopontine tract was found in PD-punding compared with patients with no impulsive-compulsive behaviours.

CONCLUSIONS

PD-punding is associated with a disconnection between midbrain, limbic and white matter tracts projecting to the frontal cortices. These alterations are at least partially independent of their psychopathological changes. Diffusion tensor MRI is a powerful tool for understanding the neural substrates underlying punding in PD.

Diffusion tensor MRI tractography reveals increased fractional anisotropy (FA) in arcuate fasciculus following music-cued motor training

Auditory cues are frequently used to support movement learning and rehabilitation, but the neural basis of this behavioural effect is not yet clear. We investigated the microstructural neuroplasticity effects of adding musical cues to a motor learning task. We hypothesised that music-cued, left-handed motor training would increase fractional anisotropy (FA) in the contralateral arcuate fasciculus, a fibre tract connecting auditory, pre-motor and motor regions. Thirty right-handed participants were assigned to a motor learning condition either with (Music Group) or without (Control Group) musical cues. Participants completed 20minutes of training three times per week over four weeks. Diffusion tensor MRI and probabilistic neighbourhood tractography identified FA, axial (AD) and radial (RD) diffusivity before and after training. Results revealed that FA increased significantly in the right arcuate fasciculus of the Music group only, as hypothesised, with trends for AD to increase and RD to decrease, a pattern of results consistent with activity-dependent increases in myelination. No significant changes were found in the left ipsilateral arcuate fasciculus of either group. This is the first evidence that adding musical cues to movement learning can induce rapid microstructural change in white matter pathways in adults, with potential implications for therapeutic clinical practice.

Advanced magnetic resonance imaging of neurodegenerative diseases

Magnetic resonance imaging (MRI) is playing an increasingly important role in the study of neurodegenerative diseases, delineating the structural and functional alterations determined by these conditions. Advanced MRI techniques are of special interest for their potential to characterize the signature of each neurodegenerative condition and aid both the diagnostic process and the monitoring of disease progression. This aspect will become crucial when disease-modifying (personalized) therapies will be established. MRI techniques are very diverse and go from the visual inspection of MRI scans to more complex approaches, such as manual and automatic volume measurements, diffusion tensor MRI, and functional MRI. All these techniques allow us to investigate the different features of neurodegeneration. In this review, we summarize the most recent advances concerning the use of MRI in some of the most important neurodegenerative conditions, putting an emphasis on the advanced techniques.

Information processing speed mediates the relationship between white matter and general intelligence in schizophrenia

Several authors have proposed that schizophrenia is the result of impaired connectivity between specific brain regions rather than differences in local brain activity. White matter abnormalities have been suggested as the anatomical substrate for this dysconnectivity hypothesis. Information processing speed may act as a key cognitive resource facilitating higher order cognition by allowing multiple cognitive processes to be simultaneously available. However, there is a lack of established associations between these variables in schizophrenia. We hypothesised that the relationship between white matter and general intelligence would be mediated by processing speed. White matter water diffusion parameters were studied using Tract-based Spatial Statistics and computed within 46 regions-of-interest (ROI). Principal component analysis was conducted on these white matter ROI for fractional anisotropy (FA) and mean diffusivity, and on neurocognitive subtests to extract general factors of white mater structure (gFA, gMD), general intelligence (g) and processing speed (gspeed). There was a positive correlation between g and gFA (r= 0.67, p =0.001) that was partially and significantly mediated by gspeed (56.22% CI: 0.10-0.62). These findings suggest a plausible model of structure-function relations in schizophrenia, whereby white matter structure may provide a neuroanatomical substrate for general intelligence, which is partly supported by speed of information processing.

Cognitive impairment in progressive supranuclear palsy-Richardson's syndrome is related to white matter damage

INTRODUCTION

Beside motor symptoms, patients with progressive supranuclear palsy syndrome (PSPs) commonly present cognitive and behavioral disorders. In this study we aimed to assess the structural brain correlates of cognitive impairment in PSPs.

METHODS

We enrolled 23 patients with probable PSP Richardson's syndrome and 15 matched healthy controls. Patients underwent an extensive clinical and neuropsychological evaluation. Cortical thickness measures and diffusion tensor metrics of white matter tracts were obtained. Random forest analysis was used to identify the strongest MRI predictors of cognitive impairment in PSPs at an individual patient level.

RESULTS

PSPs patients were in a moderate stage of the disease showing mild cognitive deficits with prominent executive dysfunction. Relative to controls, PSPs patients had a focal, bilateral cortical thinning mainly located in the prefrontal/precentral cortex and temporal pole. PSPs patients also showed a distributed white matter damage involving the main tracts including the superior cerebellar peduncle, corpus callosum, corticospinal tract, and extramotor tracts, such as the inferior fronto-occipital, superior longitudinal and uncinate fasciculi, and cingulum, bilaterally. Regional cortical thinning measures did not relate with cognitive features, while white matter damage showed a significant impact on cognitive impairment (r values ranging from -0.80 to 0.74).

CONCLUSIONS

PSPs patients show both focal cortical thinning in dorsolateral anterior regions and a distributed white matter damage involving the main motor and extramotor tracts. White matter measures are highly associated with cognitive deficits. Diffusion tensor MRI metrics are likely to be the most sensitive markers of extramotor deficits in PSPs.

Disrupted white matter structure underlies cognitive deficit in hypertensive patients

OBJECTIVES

Hypertension is considered a risk factor of cognitive impairments and could result in white matter changes. Current studies on hypertension-related white matter (WM) changes focus only on regional changes, and the information about global changes in WM structure network is limited.

METHODS

We assessed the cognitive function in 39 hypertensive patients and 37 healthy controls with a battery of neuropsychological tests. The WM structural networks were constructed by utilizing diffusion tensor tractography and calculated topological properties of the networks using a graph theoretical method. The direct and indirect correlations among cognitive impairments, brain WM network disruptions and hypertension were analyzed with structural equation modelling (SEM).

RESULTS

Hypertensive patients showed deficits in executive function, memory and attention compared with controls. An aberrant connectivity of WM networks was found in the hypertensive patients (P Eglob = 0.005, P Lp = 0.005), especially in the frontal and parietal regions. Importantly, SEM analysis showed that the decline of executive function resulted from aberrant WM networks in hypertensive patients (p = 0.3788, CFI = 0.99).

CONCLUSIONS

These results suggest that the cognitive decline in hypertensive patients was due to frontal and parietal WM disconnections. Our findings highlight the importance of brain protection in hypertension patients.

KEY POINTS

• Hypertension has a negative effect on the performance of the cognitive domains • Reduced efficiencies of white matter networks were shown in hypertension • Disrupted white matter networks are responsible for poor cognitive function in hypertension.

Propagation of pathology through brain networks in neurodegenerative diseases: from molecules to clinical phenotypes

The cellular mechanisms underlying the stereotypical progression of pathology in neurodegenerative diseases are incompletely understood, but increasing evidence indicates that misfolded protein aggregates can spread by a self-perpetuating neuron-to-neuron transmission. Novel neuroimaging techniques can help elucidating how these disorders spread across brain networks. Recent knowledge from structural and functional connectivity studies suggests that the relation between neurodegenerative diseases and distinct brain networks is likely to be a strict consequence of diffuse network dynamics. Diffusion tensor magnetic resonance imaging also showed that measurement of white matter tract involvement can be a valid surrogate to assess the in vivo spreading of pathological proteins in these conditions. This review will introduce briefly the main molecular and pathological substrates of the most frequent neurodegenerative diseases and provide a comprehensive overview of neuroimaging findings that support the "network-based neurodegeneration" hypothesis in these disorders. Characterizing network breakdown in neurodegenerative diseases will help anticipate and perhaps prevent the devastating impact of these conditions.

A selective review of structural connectivity abnormalities of schizophrenic patients at different stages of the disease

Schizophrenia has long been hypothesized to result from a disconnection syndrome due to a disruption of the association fibers of the brain. However, only with the advent of in vivo neuroimaging, a formal disconnectivity hypothesis for schizophrenia has been developed. Diffusion tensor MRI, a non-invasive technique which is sensitive to features of tissue microstructure and to the anatomy of the white matter fibers, has gained a crucial role in the field. Here, we provide a state-of-the-art review of structural connectivity abnormalities detected in schizophrenia and discuss the most relevant findings at preclinical, first episode drug-naïve, and chronic stages. Imaging studies showed white matter alterations from the preclinical to the chronic stage of the disease, which involve the corticospinal tracts, interhemispheric connections, long association white matter tracts, cerebello-thalamo-cortical circuit, and limbic system. Such abnormalities were found to be associated with the psychiatric and cognitive manifestations of the disease and to predict, at least partially, the patient clinical evolution and response to treatment.

Age-related decline in white matter integrity in a mouse model of tauopathy: an in vivo diffusion tensor magnetic resonance imaging study

Elevated expression of human hyperphosphorylated tau is associated with neuronal loss and white matter (WM) pathology in Alzheimer's disease (AD) and related neurodegenerative disorders. Using in vivo diffusion tensor magnetic resonance imaging (DT-MRI) at 11.1 Tesla we measured age-related alterations in WM diffusion anisotropy indices in a mouse model of human tauopathy (rTg4510) and nontransgenic (nonTg) control mice at the age of 2.5, 4.5, and 8 months. Similar to previous DT-MRI studies in AD subjects, 8-month-old rTg4510 mice showed lower fractional anisotropy (FA) values in WM structures than nonTg. The low WM FA in rTg4510 mice was observed in the genu and splenium of the corpus callosum, anterior commissure, fimbria, and internal capsule and was associated with a higher radial diffusivity than nonTg. Interestingly, rTg4510 mice showed lower estimates for the mode of anisotropy than controls at 2.5 months suggesting that changes in this diffusivity metric are detectable at an early stage preceding severe tauopathy. Immunogold electron microscopy partly supports our diffusion tensor imaging findings. At the age of 4 months, rTg4510 mice show axonal tau inclusions and unmyelinated processes. At later ages (12 months and 14 months) we observed inclusions in myelin sheath, axons, and unmyelinated processes, and a "disorganized" pattern of myelinated fiber arrangement with enlarged inter-axonal spaces in rTg4510 but not in nonTg mice. Our data support a role for the progression of tau pathology in reduced WM integrity measured by DT-MRI. Further in vivo DT-MRI studies in the rTg4510 mouse should help better discern the detailed mechanisms of reduced FA and anisotropy mode, and the specific role of tau during neurodegeneration.

Why diffusion tensor MRI does well only some of the time: variance and covariance of white matter tissue microstructure attributes in the living human brain

Fundamental to increasing our understanding of the role of white matter microstructure in normal/abnormal function in the living human is the development of MR-based metrics that provide increased specificity to distinct attributes of the white matter (e.g., local fibre architecture, axon morphology, and myelin content). In recent years, different approaches have been developed to enhance this specificity, and the Tractometry framework was introduced to combine the resulting multi-parametric data for a comprehensive assessment of white matter properties.

The present work exploits that framework to characterise the statistical properties, specifically the variance and covariance, of these advanced microstructural indices across the major white matter pathways, with the aim of giving clear indications on the preferred metric(s) given the specific research question.

A cohort of healthy subjects was scanned with a protocol that combined multi-component relaxometry with conventional and advanced diffusion MRI acquisitions to build the first comprehensive MRI atlas of white matter microstructure. The mean and standard deviation of the different metrics were analysed in order to understand how they vary across different brain regions/individuals and the correlation between them. Characterising the fibre architectural complexity (in terms of number of fibre populations in a voxel) provides clear insights into correlation/lack of correlation between the different metrics and explains why DT-MRI is a good model for white matter only some of the time. The study also identifies the metrics that account for the largest inter-subject variability and reports the minimal sample size required to detect differences in means, showing that, on the other hand, conventional DT-MRI indices might still be the safest choice in many contexts.

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We report an atlas of key white matter pathways in standard space.

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CHARMED provide more specific measures of axonal properties than DT-MRI metrics.

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Crossing fibres explain the correlation between myelin and diffusion indices.

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DT-MRI metrics need the smallest sample size to detect differences between groups.

Disruption of structural connectivity along the dorsal and ventral language pathways in patients with nonfluent and semantic variant primary progressive aphasia: a DT MRI study and a literature review

Nonfluent (NFV) and semantic (SV) variants of primary progressive aphasia (PPA) are associated with distinct patterns of focal cortical atrophy and underlying pathology. Previous diffusion tensor (DT) MRI studies showed a more ventral white matter (WM) involvement in SV patients and a more widespread frontal involvement in NFV. Aim of this manuscript is twofold. First, we wished to provide a brief state-of-the-art review on WM damage in PPA. Second, we used DT MRI to assess the topography of WM microstructural damage along dorsal and ventral language pathways and corpus callosum in patients with NFV and SV. Our findings show that the two PPA variants share an overlapping pattern of dorsal and ventral pathway abnormalities. In addition to these common abnormalities, variant-specific WM changes were also found, with NFV patients having a more severe damage to the dorsal (fronto-parietal) WM connections within the left superior longitudinal fasciculus/arcuate and SV patients showing a greater left ventral tract involvement (inferior longitudinal and uncinate fasciculi). These findings offer evidence that both dorsal and ventral language networks may contribute to the relatively selective deficits in NFV and SV patients.

White matter microstructural damage in Alzheimer's disease at different ages of onset

White matter (WM) microstructural damage and its relationship with cortical abnormalities were explored in early-onset Alzheimer's disease (EOAD) compared with late-onset AD (LOAD) patients. Structural and diffusion tensor magnetic resonance images were obtained from 22 EOAD patients, 35 LOAD patients, and 40 healthy controls. Patterns of WM microstructural damage and cortical atrophy, as well as their relationships, were assessed using tract-based spatial statistics, tractography and voxel-based morphometry. Compared with LOAD, EOAD patients had a more severe and distributed pattern of WM microstructural damage, in particular in the posterior fibers of cingulum and corpus callosum. In both groups with Alzheimer's disease, but especially in LOAD patients, correlations between cingulum and corpus callosum fractional anisotropy and parietal, temporal, and frontal cortical volumes were found. In conclusion, WM microstructural damage is more severe in EOAD compared with LOAD patients. Such damage follows different patterns of topographical distribution in the 2 patient groups.