Degeneration of dementia with Lewy bodies measured by diffusion tensor imaging

Longitudinal Free-Water Changes in Dementia with Lewy Bodies

BACKGROUND

Diffusion-weighted magnetic resonance imaging (dMRI) examines tissue microstructure integrity in vivo. Prior dementia with Lewy bodies (DLB) diffusion tensor imaging studies yielded mixed results.

OBJECTIVE

We employed free-water (FW) imaging to assess DLB progression and correlate with clinical decline in DLB.

METHODS

Baseline and follow-up MRIs were obtained at 12 and/or 24 months for 27 individuals with DLB or mild cognitive impairment with Lewy bodies (MCI-LB). FW was analyzed using the Mayo Clinic Adult Lifespan Template. Primary outcomes were FW differences between baseline and 12 or 24 months. To compare FW change longitudinally, we included 20 cognitively unimpaired individuals from the Alzheimer's Disease Neuroimaging Initiative.

RESULTS

We followed 23 participants to 12 months and 16 participants to 24 months. Both groups had worsening in Montreal Cognitive Assessment (MoCA) and Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) scores. We found significant FW increases at both time points compared to baseline in the insula, amygdala, posterior cingulum, parahippocampal, entorhinal, supramarginal, fusiform, retrosplenial, and Rolandic operculum regions. At 24 months, we found more widespread microstructural changes in regions implicated in visuospatial processing, motor, and cholinergic functions. Between-group analyses (DLB vs. controls) confirmed significant FW changes over 24 months in most of these regions. FW changes were associated with longitudinal worsening of MDS-UPDRS and MoCA scores.

CONCLUSIONS

FW increased in gray and white matter regions in DLB, likely due to neurodegenerative pathology associated with disease progression. FW change was associated with clinical decline. The findings support dMRI as a promising tool to track disease progression in DLB. © 2024 International Parkinson and Movement Disorder Society.

The central role of the Thalamus in psychosis, lessons from neurodegenerative diseases and psychedelics

The PD-DLB psychosis complex found in Parkinson's disease (PD) and Dementia with Lewy Bodies (DLB) includes hallucinations, Somatic Symptom/Functional Disorders, and delusions. These disorders exhibit similar presentation patterns and progression. Mechanisms at the root of these symptoms also share similarities with processes promoting altered states of consciousness found in Rapid Eye Movement sleep, psychiatric disorders, or the intake of psychedelic compounds. We propose that these mechanisms find a crucial driver and trigger in the dysregulated activity of high-order thalamic nuclei set in motion by ThalamoCortical Dysrhythmia (TCD). TCD generates the loss of finely tuned cortico-cortical modulations promoted by the thalamus and unleashes the aberrant activity of the Default Mode Network (DMN). TCD moves in parallel with altered thalamic filtering of external and internal information. The process produces an input overload to the cortex, thereby exacerbating DMN decoupling from task-positive networks. These phenomena alter the brain metastability, creating dreamlike, dissociative, or altered states of consciousness. In support of this hypothesis, mind-altering psychedelic drugs also modulate thalamic-cortical pathways. Understanding the pathophysiological background of these conditions provides a conceptual bridge between neurology and psychiatry, thereby helping to generate a promising and converging area of investigation and therapeutic efforts.

(Dis-)Connected Dots in Dementia with Lewy Bodies-A Systematic Review of Connectivity Studies

Studies on dementia with Lewy bodies (DLB) have mainly focused on the degeneration of distinct cortical and subcortical regions related to the deposition of Lewy bodies. In view of the proposed trans-synaptic spread of the α-synuclein pathology, investigating the disease only in this segregated fashion would be detrimental to our understanding of its progression. In this systematic review, we summarize findings on structural and functional brain connectivity in DLB, as connectivity measures may offer better insights on how the brain is affected by the spread of the pathology. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched Web of Science, PubMed, and SCOPUS for relevant articles published up to November 1, 2021. Of 1215 identified records, we selected and systematically reviewed 53 articles that compared connectivity features between patients with DLB and healthy controls. Structural and functional magnetic resonance imaging, positron emission tomography, single-positron emission computer tomography, and electroencephalography assessments of patients revealed widespread abnormalities within and across brain networks in DLB. Frontoparietal, default mode, and visual networks and their connections to other brain regions featured the most consistent disruptions, which were also associated with core clinical features and cognitive impairments. Furthermore, graph theoretical measures revealed disease-related decreases in local and global network efficiency. This systematic review shows that structural and functional connectivity characteristics in DLB may be particularly valuable at early stages, before overt brain atrophy can be observed. This knowledge may help improve the diagnosis and prognosis in DLB as well as pinpoint targets for future disease-modifying treatments. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Microstructural changes in prodromal dementia with Lewy bodies compared to normal aging: multiparametric quantitative MRI evidences

Dementia with Lewy bodies (DLB) patients show few significant macroscopic structural changes, especially at the early stages of the disease, making quantitative MRI especially interesting to explore more subtle changes that are not detectable by conventional volumetric techniques. Microstructural alterations have been reported in DLB at the dementia stage, but no study to date was conducted in prodromal patients. Here, quantitative MRI data were collected from 46 DLB prodromal patients and 20 healthy elderly subjects, who also underwent a detailed clinical examination including the Mayo Clinic Fluctuation Scale. We conducted voxel-wise between-group comparisons in diffusion tensor imaging (DTI) metrics and in R2* mapping, along with a multivariate analysis combining the two modalities. We highlighted multiple grey matter and white matter microstructural changes in DLB patients at the prodromal stage, compared to control subjects. Our multivariate analysis identified three distinct regional patterns of DTI and R2* changes (anterior, anteromedial, posterior) in DLB patients, that could reflect different neuropathological processes across brain regions. We also observed an association between R2* alterations in the thalamus, and the severity of fluctuations, in the DLB group. These preliminary findings are promising and require future investigations to better understand the biological underpinnings of microstructural alterations.

A multiparametric MRI study of structural brain damage in dementia with lewy bodies: A comparison with Alzheimer's disease

INTRODUCTION

Differential diagnosis between dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) is crucial for an adequate patients' management but might be challenging. We investigated with advanced MRI techniques gray (GM) and white matter (WM) damage in DLB patients compared to those with AD.

METHODS

24 DLB patients, 26 age- and disease severity-matched AD patients, and 20 age and sex-matched controls performed clinical and neuropsychological assessment, and brain structural and diffusion-tensor MRI. We measured GM atrophy using voxel-based morphometry, WM hyperintensities (WMH) using a local thresholding segmentation technique, and normal-appearing WM (NAWM) damage using tract-based spatial statistic.

RESULTS

DLB and AD patients exhibited mild-to-moderate-stage dementia. Compared to controls, GM damage was diffuse in AD, while limited to bilateral thalamus and temporal regions in DLB. Compared to DLB, AD patients exhibited GM atrophy in bilateral fronto-temporal and occipital regions. DLB and AD patients showed higher WMH load than controls, with no differences among each other. WMH in DLB were diffuse with relative prevalence in posterior parietal-occipital regions. Compared to controls, both DLB and AD patients showed reduced microstructural integrity of the main supratentorial and infratentorial NAWM tracts. AD patients exhibited greater posterior NAWM damage than DLB.

CONCLUSIONS

DLB showed prominent WM degeneration compared to the limited GM atrophy, while in AD both tissue compartments were severely involved. In DLB, NAWM microstructural degeneration was independent of WMH, thus revealing two possible underlying processes. Different pathophysiological mechanisms are likely to drive GM and WM damage distribution in DLB and AD.

Structural and Functional Magnetic Resonance Imaging of Dementia With Lewy Bodies

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer's disease (AD). Although diagnosis may be challenging, there is increasing evidence that the use of biomarkers according to 2017 revised criteria for diagnosis and management of dementia with Lewy bodies can increase diagnostic accuracy. Apart from nuclear medicine techniques, various magnetic resonance imaging (MRI) techniques have been utilized in attempt to enhance diagnostic accuracy. This chapter reviews structural, functional and diffusion MRI studies in DLB cohorts being compared to healthy controls, AD or dementia in Parkinson's disease (PDD). We also included relatively new MRI methods that may have potential to identify early DLB subjects and aim at examining brain iron and neuromelanin.

MR approaches in neurodegenerative disorders

Neurodegenerative disease is the umbrella term which refers to a range of clinical conditions causing degeneration of neurons within the central nervous system leading to loss of brain function and eventual death. The most prevalent of these is Alzheimer's disease (AD), which affects approximately 50 million people worldwide and is predicted to reach 75 million by 2030. Neurodegenerative diseases can only be fully diagnosed at post mortem by neuropathological assessment of the type and distribution of protein deposits which characterise each different condition, but there is a clear role for imaging technologies in aiding patient diagnoses in life. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques have been applied to study these conditions for many years. In this review, we consider the range of MR-based measurements and describe the findings in AD, but also contrast these with the second most common dementia, dementia with Lewy bodies (DLB). The most definitive observation is the major structural brain changes seen in AD using conventional T1-weighted (T1w) MRI, where medial temporal lobe structures are notably atrophied in most symptomatic patients with AD, but often preserved in DLB. Indeed these findings are sufficiently robust to have been incorporated into clinical diagnostic criteria. Diffusion tensor imaging (DTI) reveals widespread changes in tissue microstructure, with increased mean diffusivity and decreased fractional anisotropy reflecting the degeneration of the white matter structures. There are suggestions that there are subtle differences between AD and DLB populations. At the metabolic level, atrophy-corrected MRS demonstrates reduced density of healthy neurons in brain areas with altered perfusion and in regions known to show higher deposits of pathogenic proteins. As studies have moved from patients with advanced disease and clear dysfunction to patients with earlier presentation such as with mild cognitive impairment (MCI), which in some represents the first signs of their ensuing dementia, the ability of MRI to detect differences has been weaker and further work is still required, ideally in much larger cohorts than previously studied. The vast majority of imaging research in dementia populations has been univariate with respect to the MR-derived parameters considered. To date, none of these measurements has uniquely replicated the patterns of tissue involvement seen by neuropathology, and the ability of MR techniques to deliver a non-invasive diagnosis eludes us. Future opportunities may lie in combining MR and nuclear medicine approaches (position emission tomography, PET) to provide a more complete view of structural and metabolic changes. Such developments will require multi-variate analyses, possibly combined with artificial intelligence or deep learning algorithms, to enhance our ability to combine the array of image-derived information, genetic, gender and lifestyle factors.

Structural Connectivity is Differently Altered in Dementia with Lewy Body and Alzheimer's Disease

The structural connectivity within cortical areas and between cortical and subcortical structures was investigated in dementia with Lewy bodies (DLB) and Alzheimer’s disease (AD). We hypothesized that white matter (WM) tracts, which are linked to visual, attentional, and mnemonic functions, would be differentially and selectively affected in DLB as compared to AD and age-matched control subjects. Structural tensor imaging and diffusion tensor imaging (DTI) were performed on 14 DLB patients, 14 AD patients, and 15 controls. DTI metrics related to WM damage were assessed within tracts reconstructed by FreeSurfer’s TRActs Constrained by UnderLying Anatomy pipeline. Correlation analysis between WM and gray matter (GM) metrics was performed to assess whether the structural connectivity alteration in AD and DLB could be secondary to GM neuronal loss or a consequence of direct WM injury. Anterior thalamic radiation (ATR) and cingulum-cingulate gyrus were altered in DLB, whereas cingulum-angular bundle (CAB) was disrupted in AD. In DLB patients, secondary axonal degeneration within ATR was found in relation to microstructural damage within medio-dorsal thalamus, whereas axonal degeneration within CAB was related to precuneus thinning. WM alteration within the uncinate fasciculus was present in both groups of patients and was related to frontal and to temporal thinning in DLB and AD, respectively. We found structural connectivity alterations within fronto-thalamic and fronto-parietal (precuneus) network in DLB whereas, in contrast, disruption of structural connectivity of mnemonic pathways was present in AD. Furthermore, the high correlation between GM and WM metrics suggests that the structural connectivity alteration in DLB could be linked to GM neuronal loss rather than by direct WM injury. Thus, this finding supports the key role of cortical and subcortical atrophy in DLB.

Using structural and diffusion magnetic resonance imaging to differentiate the dementias

Dementia is one of the major causes of personal, societal and financial dependence in older people and in today's ageing society there is a pressing need for early and accurate markers of cognitive decline. There are several subtypes of dementia but the four most common are Alzheimer's disease, Lewy body dementia, vascular dementia and frontotemporal dementia. These disorders can only be diagnosed at autopsy, and ante-mortem assessments of "probable dementia (e.g. of Alzheimer type)" are traditionally driven by clinical symptoms of cognitive or behavioural deficits. However, owing to the overlapping nature of symptoms and age of onset, a significant proportion of dementia cases remain incorrectly diagnosed. Misdiagnosis can have an extensive impact, both at the level of the individual, who may not be offered the appropriate treatment, and on a wider scale, by influencing the entry of patients into relevant clinical trials. Magnetic resonance imaging (MRI) may help to improve diagnosis by providing non-invasive and detailed disease-specific markers of cognitive decline. MRI-derived measurements of grey and white matter structural integrity are potential surrogate markers of disease progression, and may also provide valuable diagnostic information. This review summarises the latest evidence on the use of structural and diffusion MRI in differentiating between the four major dementia subtypes.

Computational model of visual hallucination in dementia with Lewy bodies

Patients with dementia with Lewy bodies (DLB) frequently experience visual hallucination (VH), which has been aptly described as people seeing things that are not there. The distinctive character of VH in DLB necessitates a new theory of visual cognition. We have conducted a series of studies with the aim to understand the mechanism of this dysfunction of the cognitive system. We have proposed that if we view the disease from the internal mechanism of neurocognitive processes, and if also take into consideration recent experimental data on conduction abnormality, at least some of the symptoms can be understood within the framework of network (or disconnection) syndromes. This paper describes the problem from a computational aspect and tries to determine whether conduction disturbances in a computational model can in fact produce a "computational" hallucination under appropriate assumptions.

Neuroimaging characteristics of dementia with Lewy bodies

This review summarises the findings and applications from neuroimaging studies in dementia with Lewy bodies (DLB), highlighting key differences between DLB and other subtypes of dementia. We also discuss the increasingly important role of imaging biomarkers in differential diagnosis and outline promising areas for future research in DLB. DLB shares common clinical, neuropsychological and pathological features with Parkinson’s disease dementia and other dementia subtypes, such as Alzheimer’s disease. Despite the development of consensus diagnostic criteria, the sensitivity for differential diagnosis of DLB in clinical practice remains low and many DLB patients will be misdiagnosed. The importance of developing accurate imaging markers in dementia is highlighted by the potential for treatments targeting specific molecular abnormalities as well as the responsiveness to cholinesterase inhibitors and marked neuroleptic sensitivity of DLB. We review various brain imaging techniques that have been applied to investigate DLB, including the characteristic nigrostriatal degeneration in DLB using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) tracers. Dopamine transporter loss has proven to reliably differentiate DLB from other dementias and has been incorporated into the revised clinical diagnostic criteria for DLB. To date, this remains the 'gold standard' for diagnostic imaging of DLB. Regional cerebral blood flow, 18 F-fluorodeoxygluclose-PET and SPECT have also identified marked deficits in the occipital regions with relative sparing of the medial temporal lobe when compared to Alzheimer’s disease. In addition, structural, diffusion, and functional magnetic resonance imaging techniques have shown alterations in structure, white matter integrity, and functional activity in DLB. We argue that the multimodal identification of DLB-specific biomarkers has the potential to improve ante-mortem diagnosis and contribute to our understanding of the pathological background of DLB and its progression.

Assessment of regional MR diffusion changes in dementia with Lewy bodies and Alzheimer's disease

BACKGROUND

Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) are common forms of dementia, yet diagnosis is often difficult. Diffusion tensor imaging (DTI) is an MR technique used to assess neuronal microstructural integrity that may help develop a better understanding of the differences between the conditions.

METHODS

We recruited subjects with DLB (n = 35), AD (n = 36), and similar aged healthy controls (n = 35). T1 weighted anatomical and diffusion MR images were acquired at 3 Tesla. Region of interest (ROI) analysis was used to measure fractional anisotropy (FA) and mean diffusivity (MD) in five structures: precuneus, thalamus, pons, midbrain, and amygdala. Where appropriate diffusivity measures (FA, MD) were correlated with selected clinical measures.

RESULTS

Compared to controls, DLB subjects were characterized by reduced FA (p = 0.016) and increased MD (p = 0.007) in the precuneus. Amygdala diffusivity was positively correlated with UPDRS-III score in DLB (p = 0.003). In AD, reduced FA in the precuneus was also observed compared to controls (p = 0.026), and was associated with impaired global cognition (MMSE score) (p = 0.03).

CONCLUSIONS

Our findings highlight the potential importance of the precuneus in the pathogenesis of DLB as well as AD. Diffusion tensor MRI may shed new light on the different neurobiological changes underpinning the key clinical features of DLB and AD.

Diffusion tensor imaging in parkinsonian syndromes: a systematic review and meta-analysis

OBJECTIVES

We performed a systematic review to assess alterations in measures of diffusion tensor imaging (DTI) in parkinsonian syndromes, exploring the potential role of DTI in diagnosis and as a candidate biomarker.

METHODS

We searched EMBASE and Medline databases for DTI studies comparing parkinsonian syndromes or related dementias with controls or another defined parkinsonian syndrome. Key details for each study regarding participants, imaging methods, and results were extracted. Estimates were pooled, where appropriate, by random-effects meta-analysis.

RESULTS

Of 333 results, we identified 43 studies suitable for inclusion (958 patients, 764 controls). DTI measures detected alterations in all parkinsonian syndromes, with distribution varying differentially with disease type. Nine studies were included in a meta-analysis of the substantia nigra in Parkinson disease. A notable effect size was found for lowered fractional anisotropy in the substantia nigra for patients with Parkinson disease vs controls (-0.639, 95% confidence interval -0.860 to -0.417, p < 0.0001).

CONCLUSION

DTI may be a promising biomarker in parkinsonian syndromes and have a future role in differential diagnosis. Larger cohort studies are required to investigate some encouraging preliminary findings. Given the complexity of the parkinsonian syndromes, it is likely that any potential DTI biomarker would be used in combination with other relevant biomarkers.

Clinical applications of diffusion tensor imaging

The potential utility of diffusion tensor (DT) imaging in clinical practice is broad, and new applications continue to evolve as technology advances. Clinical applications of DT imaging and tractography include tissue characterization, lesion localization, and mapping of white matter tracts. DT imaging metrics are sensitive to microstructural changes associated with central nervous system disease; however, further research is needed to enhance specificity so as to facilitate more widespread clinical application. Preoperative tract mapping, with either directionally encoded color maps or tractography, provides useful information to the neurosurgeon and has been shown to improve clinical outcomes.

Characterizing dementia with Lewy bodies by means of diffusion tensor imaging

OBJECTIVE

To investigate patterns of in vivo white matter tract change using diffusion tensor imaging (DTI), we conducted a cross-sectional study of dementia with Lewy bodies (DLB) in comparison with Alzheimer disease (AD) and normal aging.

METHODS

The study included 106 subjects (35 with DLB, 36 with AD, and 35 elderly controls) who underwent clinical and neuropsychological assessment and diffusion tensor MRI. We used tract-based spatial statistics to investigate patterns of reduced fractional anisotropy (FA) and increased mean diffusivity (MD) across the entire white matter tract skeleton and also investigated correlations with clinical features.

RESULTS

Areas of reduced FA in subjects with DLB vs controls were found primarily in parieto-occipital white matter tracts; in AD, the changes were much more diffuse. DLB was also associated with reduced FA in the pons and left thalamus, in comparison with AD. The pattern of MD increase was diffuse in AD and DLB. We found an association between DTI parameters and impaired episodic memory, letter fluency, and severity of motor parkinsonism in DLB.

CONCLUSIONS

Despite a similar level of dementia severity, patterns of DTI changes in AD and DLB differed significantly. The selective involvement of the visual association areas and subcortical structures and the significant clinical correlations highlight the potential importance of white matter tract change in the pathogenesis of DLB. DTI may be a useful technique to investigate early and possible preclinical changes in DLB and warrants further investigation.

Differentiating dementia with Lewy bodies and Alzheimer’s disease using MRI

SUMMARY Despite the characteristic clinical differences between dementia with Lewy bodies (DLB) and Alzheimer’s disease (AD), a large degree of overlap exists. In particular, the clinical diagnostic criteria for DLB lack sensitivity so that many cases of DLB will be missed during life. MRI techniques offer a noninvasive method to assess the brain structure and function in more detail. In particular, advanced MRI methods such as diffusion-tensor imaging, functional MRI, arterial spin labeling (perfusion) and magnetic resonance spectroscopy may offer more sensitive methods to detect early and, possibly, preclinical change in dementia and contribute to our understanding of the differences between AD and DLB. This paper provides an overview of MRI changes in DLB and AD, the relationship to other imaging modalities such as single-photon emission computed tomography and PET, highlighting the differences between the conditions currently applicable to the clinical setting, as well as recent developments in MRI methods yet to be translated into large-scale clinical studies.

Visual cortex in dementia with Lewy bodies: magnetic resonance imaging study

BACKGROUND

Visual hallucinations and visuoperceptual deficits are common in dementia with Lewy bodies, suggesting that cortical visual function may be abnormal.

AIMS

To investigate: (1) cortical visual function using functional magnetic resonance imaging (fMRI); and (2) the nature and severity of perfusion deficits in visual areas using arterial spin labelling (ASL)-MRI.

METHOD

In total, 17 participants with dementia with Lewy bodies (DLB group) and 19 similarly aged controls were presented with simple visual stimuli (checkerboard, moving dots, and objects) during fMRI and subsequently underwent ASL-MRI (DLB group n = 15, control group n = 19).

RESULTS

Functional activations were evident in visual areas in both the DLB and control groups in response to checkerboard and objects stimuli but reduced visual area V5/MT (middle temporal) activation occurred in the DLB group in response to motion stimuli. Posterior cortical perfusion deficits occurred in the DLB group, particularly in higher visual areas.

CONCLUSIONS

Higher visual areas, particularly occipito-parietal, appear abnormal in dementia with Lewy bodies, while there is a preservation of function in lower visual areas (V1 and V2/3).

DTI analyses and clinical applications in Alzheimer's disease

DTI is one of the most effective MR tools for the investigation of the brain anatomy. In addition to the gray matter, histopathological studies indicate that white matter is also a good target for both the early diagnosis of AD and for monitoring disease progression, which motivates us to use DTI to study AD patients in vivo. There are already a large amount of studies reporting significant differences between AD patients and controls, as well as to predict progression of disease in symptomatic non-demented individuals. Application of these findings in clinical practice remains to be demonstrated.

Visual hallucinations in dementia with Lewy bodies: transcranial magnetic stimulation study

BACKGROUND

The aetiology of visual hallucinations is poorly understood in dementia with Lewy bodies. Pathological alterations in visual cortical excitability may be one contributory mechanism.

AIMS

To determine visual cortical excitability in people with dementia with Lewy bodies compared with aged-matched controls and also the relationship between visual cortical excitability and visual hallucinations in dementia with Lewy bodies.

METHOD

Visual cortical excitability was determined by using transcranial magnetic stimulation (TMS) applied to the occiput to elicit phosphenes (transient subjective visual responses) in 21 patients with dementia with Lewy bodies and 19 age-matched controls.

RESULTS

Phosphene parameters were similar between both groups. However, in the patients with dementia with Lewy bodies, TMS measures of visual cortical excitability correlated strongly with the severity of visual hallucinations (P = 0.005). Six patients with dementia with Lewy bodies experienced visual hallucination-like phosphenes (for example, seeing people or figures on stimulation) compared with none of the controls (P = 0.02).

CONCLUSIONS

Increased visual cortical excitability in dementia with Lewy bodies does not appear to explain visual hallucinations but it may be a marker for their severity.

Diffusion tensor imaging in Alzheimer's disease and dementia with Lewy bodies

White matter changes have been investigated in Alzheimer's disease (AD) in a number of studies using diffusion imaging. Fewer studies have investigated dementia with Lewy bodies (DLB). We used diffusion-weighted magnetic resonance imaging (MRI) and high-resolution (0.3 mm in-plane) coronal 3T MRI of the medial temporal lobe in 16 subjects with AD, 16 with DLB and 16 similarly aged healthy subjects. We found increased mean diffusivity in the temporal lobe of AD, and reduced fractional anisotropy (FA) in a small cluster in the right postcentral gyrus region in the DLB group. Mean FA in this cluster correlated with UPDRS (Unified Parkinson's Disease Rating Scale) motor score. We had previously reported reduced visibility in the AD group of a dark appearing layer of the hippocampus in the high-resolution images. In an SPM analysis on all subjects, there were significant clusters of reduced FA in the corpus callosum, fornix and stria terminalis that correlated with the visual rating of the hippocampus. These results suggest that changes to the hippocampus are associated with structural changes to the white matter fibres of the hippocampus output, and that changes in motor function are associated with changes in white matter underlying somatosensory cortex.

Other magnetic resonance imaging techniques

Relatively new developments in MRI, such as functional MRI (fMRI), magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) are rapidly developing into imaging modalities that will become clinically available in the near future. They have in common that their signal is somewhat easier to interpret than structural MRI: fMRI mirrors excess cerebral blood flow, in many cases representing brain activity, MRS gives the average volume concentrations of specific chemical compounds, and DTI reflects "directedness" of micro-anatomical structures, of particular use in white matter where fiber bundle disruption can be detected with great sensitivity. While structural changes in MRI have been disappointing in giving a diagnosis of sufficient sensitivity and specificity, these newer methods hold out hope for elucidating pathological changes and differentiating patient groups more rigorously. This paper summarizes promising research results that will yet have to be translated into real life clinical studies in larger groups of patients (e.g. memory clinic patients). Where available, we have tried to summarize results comparing different types of dementia.

Functional network disruption in the degenerative dementias

Despite advances towards understanding the molecular pathophysiology of the neurodegenerative dementias, the mechanisms linking molecular changes to neuropathology and neuropathological changes to clinical symptoms remain largely obscure. Connectivity is a distinctive feature of the brain and the integrity of functional network dynamics is crucial for normal functioning. A better understanding of network disruption in the neurodegenerative dementias might help bridge the gap between molecular changes, pathological changes, and symptoms. Recent findings on functional network disruption as assessed with resting-state or intrinsic connectivity functional MRI and electroencephalography and magnetoencephalography have shown distinct patterns of network disruption across the major neurodegenerative diseases. These network abnormalities are somewhat specific to the clinical syndromes and, in Alzheimer's disease and frontotemporal dementia, network disruption tracks the pattern of pathological changes. These findings might have practical implications for diagnostic accuracy, allowing earlier detection of neurodegenerative diseases even at the presymptomatic stage, and tracking of disease progression.

White matter changes in dementia with Lewy bodies and Alzheimer's disease: a tractography-based study

Dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) are different types of dementia. However, their clinical symptoms partially overlap and differential diagnosis is occasionally difficult. There is need for additional diagnostic criteria to reliably differentiate between these two conditions. Meanwhile, several imaging studies have showed inconsistent results between DLB and AD. The aim of this study was to use a tractography-based analysis to elucidate white matter alterations in subjects with DLB compared to those with AD and to controls. An understanding of the white matter connectivity differences between AD, DLB and controls will be helpful for differential diagnosis and an understanding of the pathophysiology. Twenty-six subjects with DLB, 26 with AD and 26 controls underwent magnetic resonance diffusion tensor imaging and neuropsychological assessment. Diffusion tensors were computed and fiber-tract maps were created using "dTV II" software. We measured mean fractional anisotropy (FA) values along the uncinate fasciculus (UNC), the inferior occipitofrontal fasciculus (IOFF) and the inferior longitudinal fasciculus (ILF). Both subjects with DLB and AD had lower FA values for the bilateral UNC than controls. Subjects with DLB exhibited significantly lower FA values on both sides of the IOFF and the left side of the ILF than those of controls. Although there were no significant differences between subjects with DLB and AD for any measurements, those with DLB exhibited lower FA values especially in visual-related white matter. These different changes in white matter tracts among groups could be helpful for differential diagnosis and an understanding of the pathophysiology.

Cognitive status correlates with white matter alteration in Parkinson's disease

Patients with Parkinson's disease (PD) can develop mild cognitive impairment (PD-MCI), frequently progressing to dementia (PDD). Here, we aimed to elucidate the relationship between white matter alteration and cognitive status in PD and dementia with Lewy bodies (DLB) by using diffusion tensor imaging. We also compared the progression patterns of white and gray matter and the cerebral perfusion. We enrolled patients with PD cognitively normal (PD-CogNL, n = 32), PD-MCI (n = 28), PDD (n = 25), DLB (n = 29), and age- and sex-matched healthy control subjects (n = 40). Fractional anisotropy (FA) map of a patient group was compared with that of control subjects by using tract-based spatial statistics. For the patient cohort, intersubject voxel-wise correlation was performed between FA values and Mini-Mental Status Examination (MMSE) scores. We also evaluated the gray matter and the cerebral perfusion by conducting a voxel-based analysis. There were significantly decreased FA values in many major tracts in patients with PD-MCI, PDD, and DLB, but not in PD-CogNL, compared with control subjects. FA values in the certain white matter areas, particularly the bilateral parietal white matter, were significantly correlated with MMSE scores in patients with PD. Patients with PDD and DLB had diffuse gray matter atrophy. All patient groups had occipital and posterior parietal hypoperfusion when compared with control subjects. Our results suggest that white matter damage underlies cognitive impairment in PD, and cognitive impairment in PD progresses with functional alteration (hypoperfusion) followed by structural alterations in which white matter alteration precedes gray matter atrophy.

Antemortem differential diagnosis of dementia pathology using structural MRI: Differential-STAND

The common neurodegenerative pathologies underlying dementia are Alzheimer's disease (AD), Lewy body disease (LBD) and frontotemporal lobar degeneration (FTLD). Our aim was to identify patterns of atrophy unique to each of these diseases using antemortem structural MRI scans of pathologically confirmed dementia cases and build an MRI-based differential diagnosis system. Our approach of creating atrophy maps using structural MRI and applying them for classification of new incoming patients is labeled Differential-STAND (Differential Diagnosis Based on Structural Abnormality in Neurodegeneration). Pathologically confirmed subjects with a single dementing pathologic diagnosis who had an MRI at the time of clinical diagnosis of dementia were identified: 48 AD, 20 LBD, 47 FTLD-TDP (pathology-confirmed FTLD with TDP-43). Gray matter density in 91 regions-of-interest was measured in each subject and adjusted for head size and age using a database of 120 cognitively normal elderly. The atrophy patterns in each dementia type when compared to pathologically confirmed controls mirrored known disease-specific anatomic patterns: AD-temporoparietal association cortices and medial temporal lobe; FTLD-TDP-frontal and temporal lobes and LBD-bilateral amygdalae, dorsal midbrain and inferior temporal lobes. Differential-STAND based classification of each case was done based on a mixture model generated using bisecting k-means clustering of the information from the MRI scans. Leave-one-out classification showed reasonable performance compared to the autopsy gold standard and clinical diagnosis: AD (sensitivity: 90.7%; specificity: 84%), LBD (sensitivity: 78.6%; specificity: 98.8%) and FTLD-TDP (sensitivity: 84.4%; specificity: 93.8%). The proposed approach establishes a direct a priori relationship between specific topographic patterns on MRI and "gold standard" of pathology which can then be used to predict underlying dementia pathology in new incoming patients.

Measurement of gray and white matter atrophy in dementia with Lewy bodies using diffeomorphic anatomic registration through exponentiated lie algebra: A comparison with conventional voxel-based morphometry

BACKGROUND AND PURPOSE

DLB is recognized as the second major form of dementia in the elderly. The regional pattern of GM atrophy in DLB highly overlaps that in AD. The aim of this study was to identify the critical pattern of atrophy in DLB by using DARTEL, which provides improved registration accuracy compared with that of conventional VBM.

MATERIALS AND METHODS

We evaluated 51 patients with probable AD, 43 patients with probable DLB, and 40 age-matched healthy controls. The pattern of GM atrophy in each group was compared by using conventional VBM and VBM-DARTEL.

RESULTS

Regional patterns of atrophy identified by using conventional VBM differed significantly from those identified by using VBM-DARTEL. A decrease in GM volume in the MTLs in both AD and DLB was identified with VBM-DARTEL; the decrease was greater in patients with AD than in those with DLB. Comparisons with healthy controls revealed that the WM volume of the whole brain was preserved in patients with DLB. In contrast, a severe bilateral decrease in WM in the MTLs was detected in patients with AD.

CONCLUSIONS

VBM-DARTEL provided more accurate results, and it enabled the identification of more localized morphologic alterations than did conventional VBM. Analysis of WM preservation in DLB could help to differentiate this condition from AD.

Dementia with Lewy bodies and Alzheimer disease: neurodegenerative patterns characterized by DTI

OBJECTIVE

To identify the patterns of diffusivity changes in patients with dementia with Lewy bodies (DLB) and Alzheimer disease (AD) and to determine whether diffusion tensor MRI (DTI) is complementary to structural MRI in depicting the tissue abnormalities characteristic of DLB and AD.

METHODS

We studied clinically diagnosed age-, gender-, and education-matched subjects with DLB (n = 30), subjects with AD (n = 30), and cognitively normal (CN) subjects (n = 60) in a case-control study. DTI was performed at 3T with a fluid-attenuated inversion recovery-based DTI sequence that enabled cortical diffusion measurements. Mean diffusivity (MD) and gray matter (GM) density were measured from segmented cortical regions. Tract-based diffusivity was measured using color-coded fractional anisotropy (FA) maps.

RESULTS

Patients with DLB were characterized by elevated MD in the amygdala and decreased FA in the inferior longitudinal fasciculus (ILF). ILF diffusivity was associated with the presence of visual hallucinations (p = 0.007), and amygdala diffusivity was associated with Unified Parkinson's Disease Rating Scale (r = 0.50; p = 0.005) in DLB. In contrast, patients with AD were characterized by elevated MD in the medial temporal, temporal, and parietal lobe association cortices and decreased FA in the fornix, cingulum, and ILF. Amygdala diffusivity was complementary to GM density in discriminating DLB from CN; hippocampal and parahippocampal diffusivity was complementary to GM density in discriminating AD from CN.

CONCLUSION

Increased amygdalar diffusivity in the absence of tissue loss in dementia with Lewy bodies (DLB) may be related to microvacuolation, a common pathology associated with Lewy body disease in the amygdala. Diffusivity measurements were complementary to structural MRI, demonstrating that measures of diffusivity on diffusion tensor MRI are valuable tools for characterizing the tissue abnormalities characteristic of Alzheimer disease and DLB.

Imaging improves diagnosis of dementia with lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of degenerative dementia after Alzheimer's disease (AD), and is clinically characterized by the progressive cognitive decline with fluctuations in cognition and alertness, recurrent visual hallucinations and Parkinsonism. Once these characteristic symptoms of DLB emerge, discriminating it from AD is relatively easy. However, in the early disease stages, the clinical symptoms of various types of dementias largely overlap and it is difficult to distinguish DLB from other neurodegenerative dementias based on clinical manifestations alone. To increase the accuracy of antemortem diagnosis of DLB, the latest diagnostic criteria incorporate findings from 123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy, or from neuroimaging such as computed tomography (CT), magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). In the present guidelines, decreased dopamine transporter uptake revealed by SPECT or PET receives the greatest importance among various neuroimaging findings and is listed as one of the suggestive features. Supportive features that commonly present but are not proven to have diagnostic specificity include relatively-preserved medial-temporal-lobe structures, occipital hypoperfusion, and abnormal MIBG myocardial scintigraphy. In this paper, we review the major findings on various neuroimaging modalities and discuss the clinical usefulness of them for the diagnosis of DLB. Although there is not enough evidence to reach the conclusion, considering the accessibility in clinical practice, in our personal views, we recommend the use of brain-perfusion SPECT and MIBG myocardial scintigraphy to improve the diagnosis of DLB.