Patterns of cerebral atrophy in dementia with Lewy bodies using voxel-based morphometry

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.

Structural and Functional Magnetic Resonance Imaging: Mild Cognitive Impairment and Alzheimer Disease

Magnetic resonance (MR) imaging is playing an increasingly pivotal role in the clinical management of dementia, including Alzheimer disease (AD). In addition to established MR imaging procedures, the introduction of advanced instrumentation such as 7-T MR imaging, as well as novel MR imaging sequences such as arterial spin labeling, MR spectroscopy, diffusion tensor imaging, and resting-state functional MR imaging, may open new pathways toward improved diagnosis of AD even in early stages of disease such as mild cognitive impairment (MCI). This article describes the typical findings of established and new MR imaging procedures in healthy aging, MCI, and AD.

Subcortical connectivity in dementia with Lewy bodies and Alzheimer's disease

BACKGROUND

Resting-state functional magnetic resonance imaging (fMRI) can be used to measure correlations in spontaneous low-frequency fluctuations in the blood oxygen level-dependent (BOLD) signal which represent functional connectivity between key brain areas.

AIMS

To investigate functional connectivity with regions hypothesised to be differentially affected in dementia with Lewy bodies (DLB) compared with Alzheimer's disease and controls.

METHOD

Fifteen participants with probable DLB, 16 with probable Alzheimer's disease and 16 controls were scanned in the resting-state using a 3T scanner. The BOLD signal time-series of fluctuations in seed regions were correlated with all other voxels to measure functional connectivity.

RESULTS

Participants with DLB and Alzheimer's disease showed greater caudate and thalamic connectivity compared with controls. Those with DLB showed greater putamen connectivity compared with those with Alzheimer's disease and the controls. No regions showed less connectivity in DLB or Alzheimer's disease v. controls, or in DLB v. Alzheimer's disease.

CONCLUSIONS

Altered connectivity in DLB and Alzheimer's disease provides new insights into the neurobiology of these disorders and may aid in earlier diagnosis.

The thalamus in cirrhotic patients with and without hepatic encephalopathy: a volumetric MRI study

BACKGROUND & AIMS

The thalamus is a major relay and filter station in the central neural system. Some previous studies have suggested that the thalamus maybe implicated in the pathogenesis of hepatic encephalopathy. The aim of our study was to investigate changing thalamic volumes in cirrhotic patients with and without hepatic encephalopathy.

METHODS

Neuropsychological tests and structural MR scanning were performed on 24 cirrhotic patients, 23 cirrhotic patients with minimal hepatic encephalopathy, 24 cirrhotic patients during their first episode of overt hepatic encephalopathy, and 33 healthy controls. Voxel-based morphometry analysis was performed to detect gray matter morphological changes. The thalamus and whole brain volume were extrapolated. A receiver operating characteristic curve analysis of thalamic volumes was used to discriminate patients with minimal hepatic encephalopathy from those with hepatic cirrhosis.

RESULTS

Thalamic volume increased in a stepwise manner in patients with progressively worse stages of hepatic encephalopathy compared to healthy subjects. Additionally, a comparison of gray matter morphometry between patients with Child-Pugh grades A, B, or C and controls revealed a progression in thalamic volumes in parallel with the degree of liver failure. Moreover, thalamic volume was significantly correlated with the number connection test A time and digit-symbol test score in cirrhotic patients with minimal hepatic encephalopathy (r=0.659, P=0.001; r=-0.577, P=0.004; respectively). The area under the receiver operating characteristic curve was 0.827 (P=0.001).

CONCLUSIONS

A significantly increased thalamic volume may be provide an objective imaging measure for predicting seizures due to minimal hepatic encephalopathy in cirrhotic patients.

In vivo evaluation of gray and white matter volume loss in the parkinsonian variant of multiple system atrophy using SPM8 plus DARTEL for VBM

In multiple system atrophy with predominant parkinsonism (MSA-P), several voxel-based morphometry (VBM) studies have revealed gray matter loss; however, the white matter volume changes have been rarely reported. We investigated the volume changes of white matter as well as gray matter by VBM. A retrospective MRI study was performed in 20 patients with MSA-P and 30 age-matched healthy controls. We applied VBM with statistical parametric mapping (SPM8) plus diffeomorphic anatomical registration through exponentiated Lie algebra (DARTEL) to explore the regional atrophy of gray and white matter in all of the MSA-P patients, 14 patients with left-side dominant and 6 patients with right-side dominant onset as compared to controls. In all of the MSA-P patients, VBM revealed a significant volume reduction of gray matter in the bilateral putamina, cerebellums and dorsal midbrain. White matter loss was located in bilateral globus pallidi, external capsules extending to the midbrain, right subcortical to precentral area through internal capsule, the pons, bilateral middle cerebellar peduncles and left cerebellum. In left-side dominant MSA-P patients, the gray and white matter volume loss was detected predominantly on the right side and vice versa in right-side dominant MSA-P patients. A correlation with disease duration and severity was not detected. VBM using SPM8 plus DARTEL detected significant volume loss not only in the gray but also in the white matter of the area affected by MSA-P.

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Volume changes of gray and white matter were investigated by VBM in MSA-P.

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Volume loss of globus pallidus with each structure was detected.

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Gray and white matter volume loss agreed well with clinical findings in laterality.

Sample entropy and regularity dimension in complexity analysis of cortical surface structure in early Alzheimer's disease and aging

We apply for the first time the sample entropy (SampEn) and regularity dimension model for measuring signal complexity to quantify the structural complexity of the brain on MRI. The concept of the regularity dimension is based on the theory of chaos for studying nonlinear dynamical systems, where power laws and entropy measure are adopted to develop the regularity dimension for modeling a mathematical relationship between the frequencies with which information about signal regularity changes in various scales. The sample entropy and regularity dimension of MRI-based brain structural complexity are computed for early Alzheimer's disease (AD) elder adults and age and gender-matched non-demented controls, as well as for a wide range of ages from young people to elder adults. A significantly higher global cortical structure complexity is detected in AD individuals (p<0.001). The increase of SampEn and the regularity dimension are also found to be accompanied with aging which might indicate an age-related exacerbation of cortical structural irregularity. The provided model can be potentially used as an imaging bio-marker for early prediction of AD and age-related cognitive decline.

Discrimination of dementia with Lewy bodies from Alzheimer's disease using voxel-based morphometry of white matter by statistical parametric mapping 8 plus diffeomorphic anatomic registration through exponentiated Lie algebra

Introduction

The purpose of this study was to identify brain atrophy specific for dementia with Lewy bodies (DLB) and to evaluate the discriminatory performance of this specific atrophy between DLB and Alzheimer’s disease (AD).

Methods

We retrospectively reviewed 60 DLB and 30 AD patients who had undergone 3D T1-weighted MRI. We randomly divided the DLB patients into two equal groups (A and B). First, we obtained a target volume of interest (VOI) for DLB-specific atrophy using correlation analysis of the percentage rate of significant whole white matter (WM) atrophy calculated using the Voxel-based Specific Regional Analysis System for Alzheimer’s Disease (VSRAD) based on statistical parametric mapping 8 (SPM8) plus diffeomorphic anatomic registration through exponentiated Lie algebra, with segmented WM images in group A. We then evaluated the usefulness of this target VOI for discriminating the remaining 30 DLB patients in group B from the 30 AD patients. Z score values in this target VOI obtained from VSRAD were used as the determinant in receiver operating characteristic (ROC) analysis.

Results

Specific target VOIs for DLB were determined in the right-side dominant dorsal midbrain, right-side dominant dorsal pons, and bilateral cerebellum. ROC analysis revealed that the target VOI limited to the midbrain exhibited the highest area under the ROC curves of 0.75.

Conclusions

DLB patients showed specific atrophy in the midbrain, pons, and cerebellum. Midbrain atrophy demonstrated the highest power for discriminating DLB and AD. This approach may be useful for determining the contributions of DLB and AD pathologies to the dementia syndrome.

Multivariate classification of patients with Alzheimer's and dementia with Lewy bodies using high-dimensional cortical thickness measurements: an MRI surface-based morphometric study

CONTEXT

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are the most common neurodegenerative dementia types. It is important to differentiate between them because of the differences in prognosis and treatment approaches.

OBJECTIVE

Investigate if sparse partial least squares (SPLS) classification of cortical thickness measurements could differentiate between AD and DLB.

METHODS

Two independent cohorts without MR-protocol alignment in Norway and Slovenia with 97 AD and DLB subjects were enrolled. Cortical thickness measurements acquired with Freesurfer were used in subsequent SPLS classification runs. The cohorts were analyzed separately and afterwards combined. The models were trained with leave-one-out cross validation and test datasets where used when available. To study the impact of MR-protocol alignment, the classifiers were additionally tested on sets drawn exclusively from the independent cohorts.

RESULTS

The obtained sensitivity/specificity/AUC values were 94.4/88.89/0.978 and 88.2/94.1/0.969 in the Norwegian and Slovenian cohorts, respectively. Both cohorts showed AD-associated pattern of thinning in mid-anterior temporal, occipital and subgenual cingulate cortex, whereas the pattern supportive for DLB included thinning in dorsal cingulate, posterior temporal and lateral orbitofrontal regions. When combining the cohorts, sensitivity/specificity/AUC were 82.1/85.7/0.948 for the training and 77.8/75/0.731 for the testing datasets with the same pattern-of-difference. The models tested on datasets drawn exclusively from the independent cohorts did not produce adequate accuracy.

CONCLUSION

SPLS classification of cortical thickness is a good method for differentiating between AD and DLB, relatively stable even for mixed data, but not when tested on completely independent data drawn from different cohorts (without MR-protocol alignment).

Quantitative neurodegenerative pathology does not explain the degree of hippocampal atrophy on MRI in degenerative dementia

OBJECTIVE

The purpose of this study was to investigate the neuropathological substrates underlying in vivo hippocampal atrophy on magnetic resonance imaging (MRI) in autopsy confirmed neurodegenerative dementia cases.

METHODS

Thirty-one neuropathologically verified cases (23 with Lewy body dementia (LBD) and eight with Alzheimer's disease (AD)) were included who had undergone an MRI scan close to death (mean 1.5 years). Manual volumetric measurements were undertaken for the hippocampus, entorhinal cortex and amygdala on MRI, along with quantitative neuropathological analysis of plaque, tangle and Lewy body pathology in the same regions. The relationship between neuropathology and MRI volumes was assessed using correlations and linear regression.

RESULTS

Hippocampal and amygdala volumes were significantly smaller in cases with AD than with LBD, but there was no difference in entorhinal cortex volume. Analysing all cases together, a significant positive correlation was observed between normalised hippocampal volume and percent area of Lewy bodies in the hippocampus (r=0.449, p=0.017) but not with tangles (r=0.059, p=0.766) or plaques (r=-0.361, p=0.119). There were no other significant correlations between regional MRI volume and measures of neuropathology. Regression analysis showed that overall diagnosis of AD rather than burden of individual pathological changes was the most significant predictor of hippocampal volume loss in autopsy confirmed cases.

CONCLUSION

Our results suggest that (i) hippocampal and amygdala but not entorhinal cortex, volumes differ between AD and LBD and (ii) factors other than current markers of neurodegenerative pathological change are responsible for atrophy of medial temporal lobe structures in AD and LBD.

A three dimensional anatomical view of oscillatory resting-state activity and functional connectivity in Parkinson's disease related dementia: An MEG study using atlas-based beamforming

Parkinson's disease (PD) related dementia (PDD) develops in up to 80% of PD patients. The present study was performed to further unravel the underlying pathophysiological mechanisms by applying a new analysis approach that uses an atlas-based MEG beamformer to provide a detailed anatomical mapping of cortical rhythms and functional interactions. Importantly, we used the phase lag index (PLI) as a measure of functional connectivity to avoid any biases due to effects of volume conduction. MEG recordings were obtained in 13 PDD and 13 non-demented PD patients. Beamforming was used to estimate spectral power and PLI in delta, theta, alpha, beta and gamma frequency bands. Compared to PD patients, PDD patients had more delta and theta power in parieto-occipital and fronto-parietal areas, respectively. The PDD patients had less alpha and beta power in parieto-temporo-occipital and frontal areas, respectively. Compared to PD patients, PDD patients had lower mean PLI values in the delta and alpha bands in fronto-temporal and parieto-temporo-occipital areas, respectively. In addition, in PDD patients connectivity between pairs of regions of interest (Brodmann areas) was stronger in the theta band and weaker in the delta, alpha and beta bands. The added value of the present results over previous studies analysing frequency-specific changes in neuronal activity in PD patients, is the anatomical framework in which we demonstrated a slowing in neuronal activity and a reduction in functional connectivity in PD related dementia. Moreover, this study shows a widespread reduction in functional connectivity between different regions in PDD.

Neuroimaging of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is a relative newcomer to the field of late-life dementia. Although a diversity of imaging methodologies is now available for the study of dementia, these have been applied most often to Alzheimer's disease (AD). Studies on DLB, although fewer, have yielded fascinating and important insights into the underlying pathophysiology of this condition and allowed clinical differentiation of DLB from other dementias. Imaging research on DLB has had significant ramifications in terms of raising the profile of DLB and helping define it as a distinctive and separate disease entity from AD.

Biomarkers in dementia with Lewy bodies: a review

BACKGROUND

Dementia with Lewy bodies (DLB) shares common clinical, neuropsychological and pathological features with other dementia subtypes, such as Alzheimer's disease (AD), making it difficult to differentiate in clinical practice. Despite the development of consensus diagnostic criteria, many cases are missed, and biomarkers to assist with diagnosis would represent important advances. Our aim was to review the literature to identify potential biomarkers that may distinguish DLB from other dementia subtypes, especially AD.

METHOD

The literature search was performed using Medline up to October 2010 for imaging studies [single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI) and amyloid imaging] and cerebrospinal fluid (CSF) markers in DLB. Individual articles were examined for additional references. The abstracts of the identified articles were read to determine the most relevant papers, which became the basis for this review.

RESULTS

The most robust evidence available was for striatal dopamine transporter activity visualised by (123) I-labelled N-(3-fluoropropyl)-2β-carbomethoxy-3β-(4-iodophenyl)nortropane ((123) I-FP-CIT) SPECT. Several other imaging techniques have also reported promising results, such as [(18) F]fluorodopa PET, which assesses nigrostriatal integrity; [(18) F]fluorodeoxyglucose PET, which assesses metabolic deficits; and meta-iodobenzylguanidine imaging, which assesses sympathetic cardiac denervation. Data from studies using CSF measures of amyloid and tau, occipital hypoperfusion on SPECT and preservation of medial temporal lobe structures on MRI suggest that they may offer less diagnostic discrimination.

CONCLUSION

Several potential biomarkers have shown good diagnostic accuracy for DLB, but apart from FP-CIT SPECT, there is now a need for larger clinical multi-site studies, as well as for studies with pathological verification of diagnosis, before their use could be recommended for routine clinical practice.

Patterns of gray matter atrophy in dementia with Lewy bodies: a voxel-based morphometry study

BACKGROUND

Dementia with Lewy bodies (DLB) is a common form of dementia characterized by visual hallucinations, cognitive fluctuation and parkinsonism. We aimed to compare the patterns of gray matter atrophy in DLB with those in Alzheimer's disease (AD) and normal aging, and to investigate the relationship between atrophy and cognitive measures.

METHODS

We used voxel-based morphometry (VBM) to investigate gray matter (GM) loss in DLB (n = 35; mean age = 78.4; MMSE = 20.3), AD (n = 36; mean age = 78.3; MMSE = 19.5) and similar aged controls (n = 35; mean age = 76.7; MMSE = 29.1). T1 weighted MRI scans were acquired at 3 Tesla from all subjects and analyzed using VBM-DARTEL in SPM8. Cognitive function was assessed using the Cambridge Cognitive Examination (CAMCOG).

RESULTS

We found reduced gray matter in temporal, parietal, occipital, and subcortical structures in DLB when compared to normal controls. The degree of atrophy was less than that observed in AD. There was significantly more medial temporal lobe atrophy in the AD group when compared with DLB. We did not find a correlation between total CAMCOG score and atrophy, but the CAMCOG memory subscale score correlated with temporal lobe atrophy in both the DLB and combined DLB/AD group.

CONCLUSIONS

DLB is associated with less gray matter atrophy and relative preservation of the medial temporal lobe when compared to AD. Degree of medial temporal atrophy may be a useful imaging biomarker and our results provide support for its inclusion in the revised consensus criteria for DLB.

Temporal lobe epilepsy with amygdala enlargement: a morphologic and functional study

BACKGROUND AND PURPOSE

Temporal lobe epilepsy (TLE) with nontumoral amygdala enlargement (AE) has been reported to be a possible subtype of TLE without hippocampal sclerosis (HS). The purpose of this study was to clarify morphologic and functional characteristics of TLE with AE (TLE + AE).

METHODS

We evaluated gray matter volume and cerebral glucose hypometabolism using magnetic resonance imaging (MRI) voxel-based morphometry (VBM) and voxel-based statistical analysis of [(18) F]-fluorodeoxyglucose positron emission tomography (FDG-PET) images in 9 patients with TLE + AE as compared with controls. For VBM analysis, we recruited 30 age- and sex-matched healthy volunteers as controls. For the comparison of FDG-PET analysis, 9 patients with definite mesial TLE with HS (MTLE + HS), and 16 age- and sex-matched healthy controls were recruited.

RESULTS

In patients with TLE + AE, a significant increase in gray matter volume was found only in the affected amygdala, and no significant decrease in gray matter volume was detected. In addition, significant glucose hypometabolism was observed in the affected amygdala, whereas significant glucose hypometabolism in the hippocampus, a prominent feature of definite MTLE+HS, was not observed.

CONCLUSIONS

TLE + AE is different from MTLE + HS from morphologic and functional points of view, and the enlarged amygdala per se is potentially an epileptic focus in patients with partial epilepsy.

Multimodality imaging characteristics of dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common cause of neurodegenerative dementia after Alzheimer's disease (AD). Our objective was to determine whether the (11)C-Pittsburgh Compound-B (PiB) retention and regional hypometabolism on positron emission tomography (PET) and regional cortical atrophy on magnetic resonance imaging (MRI) are complementary in characterizing patients with DLB and differentiating them from AD. We studied age-, gender-, and education-matched patients with a clinical diagnosis of DLB (n = 21), AD (n = 21), and cognitively normal subjects (n = 42). Hippocampal atrophy, global cortical PiB retention and occipital lobe metabolism in combination distinguished DLB from AD better than any of the measurements alone (area under the receiver operating characteristic = 0.98). Five of the DLB and AD patients who underwent autopsy were distinguished through multimodality imaging. These data demonstrate that magnetic resonance imaging and PiB positron emission tomography contribute to characterizing the distinct pathological mechanisms in patients with AD compared with DLB. Occipital and posterior parietotemporal lobe hypometabolism is a distinguishing feature of DLB and this regional hypometabolic pattern is independent of the amyloid pathology.

Brain perfusion and markers of neurodegeneration in rapid eye movement sleep behavior disorder

Potential early markers of neurodegeneration such as subtle motor signs, reduced color discrimination, olfactory impairment, and brain perfusion abnormalities have been reported in idiopathic rapid eye movement sleep behavior disorder, a risk factor for Parkinson's disease and Lewy body dementia. The aim of this study was to reproduce observations of regional cerebral blood flow abnormalities in a larger independent sample of patients and to explore correlations between regional cerebral blood flow and markers of neurodegeneration. Twenty patients with idiopathic rapid eye movement sleep behavior disorder and 20 healthy controls were studied by single-photon emission computerized tomography. Motor examination, color discrimination, and olfactory identification were examined. Patients with rapid eye movement sleep behavior disorder showed decreased regional cerebral blood flow in the frontal cortex and in medial parietal areas and increased regional cerebral blood flow in subcortical regions including the bilateral pons, putamen, and hippocampus. In rapid eye movement sleep behavior disorder, brain perfusion in the frontal cortex and occipital areas was associated with poorer performance in the color discrimination test. Moreover, a relationship between loss of olfactory discrimination and regional cerebral blood flow reduction in the bilateral anterior parahippocampal gyrus, a region known to be involved in olfactory functions, was found. This study provides further evidence of regional cerebral blood flow abnormalities in rapid eye movement sleep behavior disorder that are similar to those seen in Parkinson's disease and Lewy body dementia. Moreover, regional cerebral blood flow anomalies were associated with markers of neurodegeneration.

Neuropathological correlates of volumetric MRI in autopsy-confirmed Lewy body dementia

The objective of this study was to determine the neuropathological correlates of regional medial temporal lobe volume measures on magnetic resonance imaging (MRI) in subjects with Lewy body dementia (LBD). Twenty-three autopsy-confirmed LBD cases with an MRI scan close to death (mean 1.5 years) were studied. MRI-based volumetric measures were calculated for total intracranial volume, hippocampus, entorhinal cortex, and amygdala. Quantitative neuropathological analysis of plaques, tangles, and Lewy bodies were carried out in the same regions. Spearman's rho was used to examine correlations between MRI volumes and neuropathology measures and linear regression to assess the relationship between neuropathology and MRI volumes. A significant inverse correlation was observed between normalized amygdala volume and percent area of Lewy bodies in the amygdala (r = -0.461, p = 0.035). There were no other significant correlations between regional MRI volume and measures of neuropathology. Lewy body, but not Alzheimer's disease (AD) pathology was associated with reduced amygdala volume in pathologically-verified LBD cases but neither Lewy body nor Alzheimer's disease pathology was associated with volume loss in the hippocampus or entorhinal cortex, suggesting other neuropathological factors account for atrophy in these structures in LBD.

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.

Neuroimaging for Lewy body disease: is the in vivo molecular imaging of α-synuclein neuropathology required and feasible?

Alpha-synuclein aggregation is a neuropathological hallmark of many neurodegenerative diseases including Parkinson's disease (PD), Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB), collectively termed the α-synucleinopathies. Substantial advances in clinical criteria and neuroimaging technology over the last 20 years have allowed great strides in the detection and differential diagnosis of these disorders. Nevertheless, it is clear that whilst the array of different imaging modalities in clinical use allow for a robust diagnosis of α-synucleinopathy in comparison to healthy subjects, there is no clear diagnostic imaging marker that affords a reliable differential diagnosis between the different forms of Lewy body disease (LBD) or that could facilitate tracking of disease progression. This has led to a call for a biomarker based on the pathological hallmarks of these diseases, namely α-synuclein-positive Lewy bodies (LBs). This potentially may be advantageous in terms of early disease detection, but may also be leveraged into a potential marker of disease progression. We here aim to firstly review the current status of neuroimaging biomarkers in PD and related synucleinopathies. Secondly, we outline the rationale behind α-synuclein imaging as a potential novel biomarker as well as the potential benefits and limitations of this approach. Thirdly, we attempt to illustrate the likely technical hurdles to be overcome to permit successful in vivo imaging of α-synuclein pathology in the diseased brain. Our overriding aim is to provide a framework for discussion of how to address this major unmet clinical need.

Ways toward an early diagnosis in Alzheimer's disease: the Alzheimer's Disease Neuroimaging Initiative (ADNI)

With the increasing life expectancy in developed countries, the incidence of Alzheimer's disease (AD) and thus its socioeconomic impact are growing. Increasing knowledge over the last years about the pathomechanisms involved in AD allow for the development of specific treatment strategies aimed at slowing down or even preventing neuronal death in AD. However, this requires also that (1) AD can be diagnosed with high accuracy, because non-AD dementias would not benefit from an AD-specific treatment; (2) AD can be diagnosed in very early stages when any intervention would be most effective; and (3) treatment efficacy can be reliably and meaningfully monitored. Although there currently is no ideal biomarker that would fulfill all these requirements, there is increasing evidence that a combination of currently existing neuroimaging and cerebrospinal fluid (CSF) and blood biomarkers can provide important complementary information and thus contribute to a more accurate and earlier diagnosis of AD. The Alzheimer's Disease Neuroimaging Initiative (ADNI) is exploring which combinations of these biomarkers are the most powerful for diagnosis of AD and monitoring of treatment effects.

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.

Detection of changes in cerebrospinal fluid space in idiopathic normal pressure hydrocephalus using voxel-based morphometry

INTRODUCTION

We attempted to detect alterations in the cerebrospinal fluid (CSF) space in patients with idiopathic normal pressure hydrocephalus (iNPH) using voxel-based morphometry (VBM).

METHODS

We obtained sagittal volume images of the entire head by three-dimensional T1-weighted magnetic resonance imaging and compared the regional distribution of CSF in 12 patients with iNPH, 14 patients with Alzheimer's disease (AD), and 17 healthy individuals using VBM with automatically extracted CSF objects.

RESULTS

VBM demonstrated significant widening at the lateral ventricles and Sylvian fissures and narrowing of the CSF space at the high convexity/midline areas in iNPH patients, compared to the AD patients and healthy controls (p < 0.05, after correction with a false-discovery rate). In addition, the ratio of the CSF volume in the lateral ventricle/Sylvian fissure area to that in the high convexity/midline area in iNPH patients (3.9 +/- 1.2) was remarkably greater than that in AD patients (1.2 +/- 0.3) and controls (0.9 +/- 0.3; one-way ANOVA, p < 0.001; post hoc Tukey's test, p < 0.001); we could discriminate iNPH patients from those in the other two groups without any overlap, when using a cutoff level of 1.9.

CONCLUSION

VBM using CSF objects can be used to delineate the characteristic alteration of the CSF space in iNPH patients, which has been evaluated by visual interpretation.

Forebrain overexpression of alpha-synuclein leads to early postnatal hippocampal neuron loss and synaptic disruption

Transgenic (Tg) mouse models of Parkinson's disease (PD) generated to date have primarily been designed to overexpress human alpha-synuclein (alpha-syn) to recapitulate PD-like motor impairments as well as PD-like nigrostriatal degeneration and alpha-syn pathology. However, cognitive impairments and cortical alpha-syn pathology are also common in PD patients. To model these features of PD, we created forebrain-specific conditional Tg mice that overexpress human wild type (WT) or A53T mutant alpha-syn. Here we show that both WT and A53T mutant alpha-syn lead to massive degeneration of postmitotic neurons in the hippocampal dentate gyrus (DG) during postnatal development, with hippocampal synapse loss as evidenced by reduced levels of pre- and postsynaptic markers. However, when mutant and WT alpha-syn expression was repressed until the Tg mice were mature postnatally and then induced for several months, no hippocampal neuron loss was observed. These data imply that developing neurons are more vulnerable to degenerate than mature neurons as a consequence of forebrain WT and mutant alpha-syn overexpression.

Degeneration of dementia with Lewy bodies measured by diffusion tensor imaging

Dementia with Lewy bodies (DLB) is the second most common form of dementia. It is thought to involve impairment of the visual association area. In this study, we applied diffusion tensor imaging (DTI) to examine the microstructural interruption of visual association areas in patients with DLB. The DTI metrics of three visual association fibres - the inferior longitudinal fasciculus (ILF), visual pathway, and splenial fibres - were compared between 14 patients with DLB and 13 healthy subjects. The fractional anisotropy value of the ILF was significantly lower in patients with DLB than in healthy subjects. The difference in the mean diffusivity value of ILF was at trend level. The lambda(2),(3) of ILF were significantly lower in patients with DLB; however, there was no difference in lambda(1). DTI metrics of the visual pathway and splenial fibres showed no differences between the groups. Our results showed degeneration of the ILF, which is responsible for visuospatial cognition. ILF dysfunction may influence the clinical features in DLB.

Voxel-based morphometry and Voxel-based relaxometry in parkinsonian variant of multiple system atrophy

BACKGROUND AND PURPOSE

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder divided into a parkinsonian (MSA-P) and a cerebellar variant. The purpose of this study was to assess regional brain atrophy and iron content using Voxel-based morphometry (VBM) and Voxel-based relaxometry (VBR) respectively, in MSA-P.

METHODS

Using biological parametric mapping the effect of brain atrophy was evaluated in T2 relaxation time (T2) measurements by applying analysis of covariance (ANCOVA) and correlation analysis to the VBM and VBR data. Eleven patients with MSA-P (aged 61.9 +/- 11.7 years, disease duration 5.42 +/- 2.5 years) and 11 controls were studied.

RESULTS

In comparison to the controls the patients showed decreased gray matter in the putamen, the caudate nuclei, the thalami, the anterior cerebellar lobes, and the cerebral cortex, and white matter atrophy in the pons, midbrain, and peduncles. VBR analysis showed prolonged T2 in various cortical regions. On ANCOVA, when controlling for gray and white matter volume, these regions of prolonged T2 were shrunk. Negative correlation was demonstrated between T2 and gray and white matter volume.

CONCLUSIONS

Diffuse brain atrophy, mainly in the motor circuitry is observed in MSA-P. Normalization for atrophy should always be performed in T2 measurements.

Validation of a fully automated hippocampal segmentation method on patients with dementia

We describe a fully automated method for hippocampal segmentation. The method uses SPM5 (http://www.fil.ion.ucl.ac.uk/spm/) software to segment the brain into grey/white matter, and spatially normalize the images to standard space. Grey matter pixels within a predefined hippocampal region in standard space are identified to segment the hippocampi. The method was validated on 36 subjects (9 each of Alzheimer's disease, dementia with Lewy bodies, vascular dementia, and healthy controls). The mean absolute difference in volume compared with manual segmentation was 11% (SD 9%). Linear regression between manual and automated volume gave V(auto) = V(manual) x 0.83 + 401 ml. The method provides an acceptable automated alternative to manual segmentation which may be of value in large studies.

Support vector machine-based classification of Alzheimer's disease from whole-brain anatomical MRI

PURPOSE

We present and evaluate a new automated method based on support vector machine (SVM) classification of whole-brain anatomical magnetic resonance imaging to discriminate between patients with Alzheimer's disease (AD) and elderly control subjects.

MATERIALS AND METHODS

We studied 16 patients with AD [mean age +/- standard deviation (SD) = 74.1 +/- 5.2 years, mini-mental score examination (MMSE) = 23.1 +/- 2.9] and 22 elderly controls (72.3 +/- 5.0 years, MMSE = 28.5 +/- 1.3). Three-dimensional T1-weighted MR images of each subject were automatically parcellated into regions of interest (ROIs). Based upon the characteristics of gray matter extracted from each ROI, we used an SVM algorithm to classify the subjects and statistical procedures based on bootstrap resampling to ensure the robustness of the results.

RESULTS

We obtained 94.5% mean correct classification for AD and control subjects (mean specificity, 96.6%; mean sensitivity, 91.5%).

CONCLUSIONS

Our method has the potential in distinguishing patients with AD from elderly controls and therefore may help in the early diagnosis of AD.

Role of imaging techniques in the diagnosis of dementia

Dementia is a common and growing problem, affecting 5% of the over 65 s and 20% of the over 80s. The recent availability of new treatments for dementia, as well as the importance of subtype-specific management, has renewed interest in the use of brain imaging techniques that can assist in the accurate recognition of Alzheimer's disease (AD), dementia with Lewy bodies (DLB), vascular dementia (VaD) and frontotemporal dementia (FTD). Structural imaging, historically used to exclude an intracerebral lesion as a cause for dementia, is increasingly playing a role in "ruling in" diagnoses, with atrophy of the hippocampus and entorhinal cortex an early and sensitive marker for AD, and cortical and subcortical infarcts and white matter lesions characteristic of VaD. Regionally distinct patterns of hypoperfusion on single-photon emission computed tomography (SPECT) or hypometabolism on positron emission tomography (PET) can help differentiate FTD, AD and VaD, and dopaminergic loss in the basal ganglia can differentiate DLB from AD. Newer techniques show great promise to detect specific neuroreceptor changes as well as pathological underpinnings of dementia, such as amyloid and tau pathology.

Brain volumetrics to investigate aging and the principal forms of degenerative cognitive decline: a brief review

The volume of the brain and of some of its structures can provide insight into the pathological process of several diseases. For this reason, in the recent years we saw a tremendous progress in the development of automated techniques for gaining information about global and regional atrophy. This paper reviews the main methods of analysis to quantify brain volume, and their application to the study of normal aging and the principal forms of degenerative dementias.

Diffusion tensor MRI to investigate dementias: a brief review

Diffusion tensor magnetic resonance imaging (DT-MRI) is a powerful quantitative technique with the ability to detect in vivo microscopic characteristics and abnormalities of brain tissue. It has been successfully applied to a number of neurological conditions, such as stroke, multiple sclerosis and brain tumors, providing information otherwise inaccessible on the pathological substrates. DT-MRI has also been used to study patients with cognitive decline, mainly those with Alzheimer's disease. Several image-analysis approaches have been employed, including region of interest, histogram, voxel-based analyses and DT-MRI-based tractography. Specific patterns of spatial distribution of tissue damage and correlations with neuropsychological measures have been reported. This review focuses on the use of DT-MRI to investigate dementias. The main clinical results and the different methods of image analysis will be overviewed and discussed.

MRI confirms mild cognitive impairments prodromal for Alzheimer's, vascular and Parkinson-Lewy body dementias

OBJECTIVES

MRI assessments were correlated with serial Combined Mini-Mental Cognitive Capacity Screening Examinations (CMC). Vascular-MCI (VMCI), Neurodegenerative MCI (NMCI) and Parkinson-Lewy body MCI (PLB-MCI) were compared during conversions to dementia. Mild cognitive impairments (MCI) are identifiable prodromes for all dementia subtypes. MRI abnormalities are characterized among MCI subjects prodromal for dementia of Alzheimer's disease (DAT), vascular dementia (VaD) and Parkinson-Lewy body dementia (PLBD).

METHODS

Aging volunteers (n=166) were recruited from ongoing longitudinal studies of aging, stroke, cerebrovascular disease and dementia. Cognitively normal (CN, n=52), MCIs of neurodegenerative (N-MCI, n=30), vascular (V-MCI, n=35) and Parkinson-Lewy Body (PLB-MCI, n=8) subtypes, plus converted DAT (n=19), VaD (n=17) and PLBD (n=5) were all diagnosed according to established protocol recommendations. Cerebral MRI abnormalities were likewise intercorrelated utilizing quantitative volumetric measurements.

RESULTS

V-MCI and converted VaD showed extensive leukoaraiosis with more lacunar infarcts than subjects with N-MCI or PLB-MCI. N-MCI, prodromal for DAT, showed medial temporal atrophy, greater enlargement of temporal horns, and fewer vascular lesions. PLB-MCI, prodromal for PLBD, displayed third ventricular enlargement greater than N-MCI and V-MCI, with similar but less severe atrophy of medial temporal lobe than N-MCI and fewer vascular lesions than V-MCI. Cognitive Impairments due to PLB with vascular features (V-PLB-CI) showed more lacunar and microvascular lesions involving both white matter and basal ganglia with greater frontal horn enlargement.

CONCLUSIONS

This study confirms different MCI subtypes prior to conversion to different dementias listed, recognizable by specific MRI abnormalities.

Age and dementia-associated atrophy predominates in the hippocampal head and amygdala in Parkinson's disease

The hippocampus (HC) and amygdala (AG) decrease in volume with age and in Parkinson's disease (PD) with (PDD) and without dementia. We compared 44 PD to 44 age, sex and education-matched subjects without PD (non-PD) and 13 PDD subjects. T1-weighted MR images were used to manually segment the head, body and tail of the HC and the AG. HC volumes, corrected to intracranial volume, were smaller in PDD than non-PD (p=0.04), reflected predominantly by head atrophy. Right AG volumes were smaller in PD compared to non-PD (p=0.03). HC volumes in older (>70), but not younger, non-demented PD differed from non-PD (HC, p=0.02; head, p=0.03). Age correlated negatively with overall HC (r=-0.43, p=0.004) and head (r=-0.48, p=0.001) in PD, but not in non-PD. In PD, left HC head volumes correlated with recall, but not recognition scores on the CVLT-II (r=0.35, p=0.02) and BVMT-R (r=0.35, p=0.02); AG volumes correlated with CVLT-II recall (r=0.35, p=0.02). No correlations were found in non-PD (p>0.4). In conclusion, functionally meaningful age-associated hippocampal and amygdala atrophy occurs in PD.

Atrophy is associated with posterior cingulate white matter disruption in dementia with Lewy bodies and Alzheimer's disease

Hippocampal atrophy and posterior cingulate hypometabolism are common features of both Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). These regions show correlated activity at rest as part of the 'default network', and they are connected by the cingulum, a white matter (WM) tract. We hypothesised that hippocampal atrophy would be associated with disruption of the cingulum, as determined by diffusion tensor imaging. We recruited 15 people with AD, 16 with DLB, and 15 healthy control subjects of similar age. They were scanned on a 1.5 T MRI system with a T1 weighted 3D sequence and diffusion tensor FLAIR imaging. The T1 images were segmented into grey and white matter and spatially normalised using SPM. Hippocampal atrophy was estimated by calculating the mean grey matter (GM) volume from a region of interest in standard space and global atrophy from the total CSF segmentation. Fractional anisotropy (FA) maps were calculated and also spatially normalised. Using SPM, a multivariate correlation of FA against hippocampal GM, global atrophy and disease group was performed. We found a bilateral region adjacent to the posterior cingulate and encompassing a branch of the cingulum where global atrophy correlated with fractional anisotropy, after controlling for diagnosis and hippocampal GM. The results suggest that dementia disease progression as measured by global atrophy is associated with disruption of the white matter which connects posterior cingulate and lateral parietal regions. Hence, in addition to the hypometabolism in these regions in AD and DLB, there is also disruption to the white matter connecting them. Future studies are needed to determine whether the disruption precedes or is consequent on atrophy or hypometabolism.

The role of 123I-metaiodobenzylguanidine myocardial scintigraphy in the diagnosis of Lewy body disease in patients with dementia in a memory clinic

Reduction in cardiac (123)I-metaiodobenzylguanidine (MIBG) uptake is a characteristic feature of Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and is useful in distinguishing them from other neurodegenerative disorders. The aim of this study was to investigate the role of this method of scintigraphy in the differential diagnosis of dementia in our Memory Clinic. We performed MIBG scintigraphy in patients with dementia referred to the Memory Clinic and compared the heart-to-mediastinum (H/M) ratio of MIBG uptake. Thirty out of 32 patients with DLB and all 9 PD with dementia patients had reduced H/M ratios, whereas 37 out of 40 patients with Alzheimer's disease had normal H/M ratios. Most patients with vascular dementia, frontotemporal dementia, and other dementias had normal H/M ratios. The overall sensitivity to positively identify patients with Lewy body disease (including DLB and PD with dementia) was 95%, and the specificity to distinguish them from patients with other types of dementias was 87%. MIBG scintigraphy showed a high sensitivity for the detection of Lewy body disease, and also a high specificity for discrimination from other types of dementia. The scintigraphy may provide a valuable and adjunctive method in the diagnosis of Lewy body disease and a differential diagnostic tool for patients with dementias.

Quantitative MR imaging in Alzheimer disease

Alzheimer disease (AD) is the most common type of dementia. It currently affects approximately 4 million people in the United States. AD is a progressive neurodegenerative disorder characterized by the gradual deposition of neuritic plaques and neurofibrillary tangles in the brain, which is thought to occur decades before the onset of clinical symptoms. Identification of people at risk before the clinical appearance of dementia has become a priority due to the potential benefits of therapeutic intervention. Although atrophy of medial temporal lobe structures has been shown to correlate with progression of AD, a growing number of recent reports have indicated that such atrophy may not be specific to AD. To improve diagnostic specificity, new quantitative magnetic resonance (MR) imaging methods are being developed that exploit known pathogenic mechanisms exclusive to AD. This article reviews the MR techniques that are currently available for the diagnostic assessment of AD.

Cortical atrophy in the cerebellar variant of multiple system atrophy: a voxel-based morphometry study

This study aimed to determine in vivo the atrophy patterns in clinically established cerebellar variant of multiple-system atrophy (MSA-C) using voxel-based morphometry (VBM). Thirteen patients with MSA-C (12 probable, 1 possible) and 13 healthy controls matched for age and sex were included. High-resolution MR images were acquired with a 1.5 T scanner. Images were normalized onto a study-specific template, segmented into the tissue compartments, modulated with the Jacobian determinants, and finally smoothed with a Gaussian kernel filter of 10 mm. The general linear model was used to assess statistical differences in gray and white matter. Infratentorial atrophy was observed in the cerebellar hemispheres, vermis, mesencephalon, and pons of MSA-C patients. Supratentorial volume loss was found in orbitofrontal and mid-frontal regions as well as in temporomesial and insular areas of both hemispheres. A negative correlation was observed between a cerebellar ataxia score and the volume of cerebellar hemispheres, peduncles, and pons. To compare this atrophy pattern to that of spinocerebellar ataxia (SCA2), which was previously reported by our group, a conjunction analysis was assessed. We observed a volume loss shared by both disorders comprising the cerebellum, vermis, pons, mesencephalon, orbitofrontal, mid-frontal, and temporomesial cortex of both hemispheres as well as the left insular cortex.

In vivo SPECT imaging of muscarinic acetylcholine receptors using (R,R) 123I-QNB in dementia with Lewy bodies and Parkinson's disease dementia

INTRODUCTION

Alterations in cholinergic function have been reported to be associated with dementia. The aim of this study was to investigate differences in the distribution of muscarinic acetylcholine receptors (mAChRs) using (R,R) 123I-iodo-quinuclidinyl-benzilate (QNB) and single photon emission computed tomography (SPECT) in dementia with Lewy bodies (DLB), Parkinson's disease dementia (PDD) and age-matched controls. 123I-QNB binding was also compared to the corresponding cerebral perfusion changes in the same subjects.

METHODS

63 subjects (24 controls, 14 DLB, 25 PDD) underwent 123I-QNB and perfusion 99mTc-exametazine SPECT scanning. Image analysis, using statistical parametric mapping (SPM99), involved spatial normalisation of each image to a customised template, followed by smoothing and intensity normalisation of each image to its corresponding mean whole brain uptake. Group effects and correlations were assessed using two sample t tests and linear regression respectively.

RESULTS

Relative to controls, significant elevation of 123I-QNB binding was apparent in the right occipital lobe in DLB and right and left occipital lobes in PDD (height threshold p<or=0.001 uncorrected). PDD also showed significant loss in uptake in frontal regions and temporal lobes bilaterally that was not present in DLB. These patterns appeared to be independent of any corresponding rCBF changes.

CONCLUSION

Significant elevation of mAChRs in the occipital lobe was associated with DLB and PDD. This may relate to the visual disturbances that are prevalent in these disorders. Further studies are required in order to establish the role of mAChRs in visual function.

Magnetic resonance imaging of Alzheimer's disease

A modern challenge for neuroimaging techniques is to contribute to the early diagnosis of neurodegenerative diseases, such as Alzheimer's disease (AD). Early diagnosis includes recognition of pre-demented conditions, such as mild cognitive impairment (MCI) or having a high risk of developing AD. The role of neuroimaging therefore extends beyond its traditional role of excluding other conditions such as neurosurgical lesions. In addition, early diagnosis would allow early treatment using currently available therapies or new therapies in the future. Structural imaging can detect and follow the time course of subtle brain atrophy as a surrogate marker for pathological processes. New MR techniques and image analysis software can detect subtle brain microstructural, perfusion or metabolic changes that provide new tools to study the pathological processes and detect pre-demented conditions. This review focuses on markers of macro- and microstructural, perfusion, diffusion and metabolic MR imaging and spectroscopy in AD.

Imaging correlates of posterior cortical atrophy

The aim of this study was to compare patterns of cerebral atrophy on MRI, and neurochemistry on magnetic resonance spectroscopy (MRS), in patients with posterior cortical atrophy (PCA) and typical Alzheimer's disease (AD). Voxel-based morphometry was used to assess grey matter atrophy in 38 patients with PCA, 38 patients with typical AD, and 38 controls. Clinical data was assessed in all PCA patients. Single voxel (1)H MRS located in the posterior cingulate was analyzed in a subset of patients with PCA, typical AD, and control subjects. PCA showed a pattern of atrophy affecting occipital, parietal and posterior temporal lobes, compared to controls. The pattern was bilateral, but more severe on the right. Patients with PCA showed greater atrophy in the right visual association cortex than patients with typical AD, whereas those with AD showed greater atrophy in the left hippocampus than those with PCA. (1)H MRS suggested loss of neuronal integrity and glial activation in subjects with PCA and typical AD. The differing patterns of atrophy on MRI suggest that PCA should be considered a distinct entity from typical AD.