Sequential relationships between grey matter and white matter atrophy and brain metabolic abnormalities in early Alzheimer's disease

Linking white matter integrity loss to associated cortical regions using structural connectivity information in Alzheimer's disease and fronto-temporal dementia: the Loss in Connectivity (LoCo) score

It is well known that gray matter changes occur in neurodegenerative diseases like Alzheimer's (AD) and fronto-temporal dementia (FTD), and several studies have investigated their respective patterns of atrophy progression. Recent work, however, has revealed that diffusion MRI that is able to detect white matter integrity changes may be an earlier or more sensitive biomarker in both diseases. However, studies that examine white matter changes only are limited in that they do not provide the functional specificity of GM region-based analysis. In this study, we develop a new metric called the Loss in Connectivity (LoCo) score that gives the amount of structural network disruption incurred by a gray matter region for a particular pattern of white matter integrity loss. Leveraging the relative strengths of WM and GM markers, this metric links areas of WM integrity loss to their connected GM regions as a first step in understanding their functional implications. The LoCo score is calculated for three groups: 18AD, 18 FTD, and 19 age-matched normal controls. We show significant correlations of the LoCo with the respective atrophy patterns in AD (R=0.51, p=2.2 × 10(-9)) and FTD (R=0.49, p=2.5 × 10(-8)) for a standard 116 region gray matter atlas. In addition, we demonstrate that the LoCo outperforms a measure of gray matter atrophy when classifying individuals into AD, FTD, and normal groups.

White matter integrity and reaction time intraindividual variability in healthy aging and early-stage Alzheimer disease

Aging and early-stage Alzheimer disease (AD) have been shown to be associated with increased RT intraindividual variability (IIV, as reflected by the coefficient of variation) and an exaggeration of the slow tail of the reaction time (RT) distribution in attentional control tasks, based on ex-Gaussian analyses. The current study examined associations between white matter volume, IIV, and ex-Gaussian RT distribution parameters in cognitively normal aging and early-stage AD. Three RT attention tasks (Stroop, Simon, and a consonant-vowel odd-even switching task) in conjunction with MRI-based measures of cerebral and regional white matter volume were obtained in 133 cognitively normal and 33 early-stage AD individuals. Larger volumes were associated with less IIV and less slowing in the tail of the RT distribution, and larger cerebral and inferior parietal white matter volumes were associated with faster modal reaction time. Collectively, these results support a role of white matter integrity in IIV and distributional skewing, and are consistent with the hypothesis that IIV and RT distributional skewing are sensitive to breakdowns in executive control processes in normal and pathological aging.

Visuospatial processing in early Alzheimer's disease: a multimodal neuroimaging study

INTRODUCTION

Dorsal pathway dysfunctions are thought to underlie visuospatial processing problems in Alzheimer disease (AD). Prior studies reported compensatory mechanisms in the dorsal or ventral pathway in response to these functional changes. Since functional and structural connectivity are interrelated, these functional changes could be interpreted as a disconnection between both pathways. To better understand functional alterations in the dorsal pathway, we combined functional imaging with diffusion tensor imaging (DTI) in patients with mild cognitive impairment (MCI), a likely prodromal stage of AD.

METHODS

Eighteen older male individuals with amnestic MCI (aMCI) and 18 male cognitively healthy individuals, matched for age (range 59-75 years) and education, performed an object recognition task in the Magnetic Resonance Imaging (MRI) scanner. Neural activation was measured during recognition of non-canonically versus canonically oriented objects. Regions showing activation differences between groups were also investigated by DTI.

RESULTS

Recognition of non-canonical objects elicited increased frontal, temporal and parietal activation. Combining the functional MRI (fMRI) with the DTI results showed less deactivation in areas with decreased diffusion (mediolateral parietal and orbitofrontal) and increased activation in areas with increased diffusion (parietal and temporal) in aMCI patients. Finally, in aMCI patients decreased diffusion was found in the hippocampal cingulum, connecting both pathways.

CONCLUSIONS

Our results showed increased activation in early AD patients in ventral and dorsal pathways. A decrease in deactivation and diffusion suggests functional reorganization, while increased activation and diffusion suggests compensatory processes. This is the first study showing structural evidence for functional reorganization, which may be related to connectivity loss in the cingulum.

Estrogen regulation of mitochondrial bioenergetics: implications for prevention of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. Increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. Compromised aerobic glycolysis pathway coupled with oxidative stress is first accompanied by a shift toward a ketogenic pathway that eventually progresses into fatty acid oxidation (FAO) pathways and leads to white matter degeneration and overproduction and mitochondrial accumulation of β-amyloid. Estrogen-induced signaling pathways converge upon the mitochondria to enhance mitochondrial function and to sustain aerobic glycolysis coupled with citric acid cycle-driven oxidative phosphorylation to potentiate ATP (Adenosine triphosphate) generation. In addition to potentiated mitochondrial bioenergetics, estrogen also enhances neural survival and health through maintenance of calcium homeostasis, promotion of antioxidant defense against free radicals, efficient cholesterol trafficking, and beta amyloid clearance. Significantly, the convergence of E2 mechanisms of action onto mitochondria is also a potential point of vulnerability when activated in diseased neurons that exacerbates degeneration through increased load on dysregulated calcium homeostasis. The "healthy cell bias of estrogen action" hypothesis examines the role that regulating mitochondrial function and bioenergetics play in promoting neural health and the mechanistic crossroads that lead to divergent outcomes following estrogen exposure. As the continuum of neurological health progresses from healthy to unhealthy, so too do the benefits of estrogen or hormone therapy.

Role of hippocampal CA1 atrophy in memory encoding deficits in amnestic Mild Cognitive Impairment

Identifying the specific substrates of memory deficits in early Alzheimer's disease would help to develop clinically-relevant therapies. The present study assesses the relationships between encoding versus retrieval deficits in patients with amnestic Mild Cognitive Impairment (aMCI) and atrophy specifically within the hippocampus and throughout the white matter. Twenty-two aMCI patients underwent T1-weighted MRI scans and neuropsychological testing. Grey matter and white matter segments obtained from the MRI images were each entered in correlation analyses, assessed only in the hippocampus for grey matter segments, with encoding and retrieval memory performances. For the grey matter segments, the resulting spmT correlation maps were then superimposed onto a 3D surface view of the hippocampus to identify the relative involvement of the different subfields, a method already used and validated elsewhere. Memory encoding deficits specifically correlated with CA1 subfield atrophy, while no relationship was found with white matter atrophy. In contrast, retrieval deficits were weakly related to hippocampal atrophy and did not involve a particular subfield, while they strongly correlated with loss of white matter, specifically in medial parietal and frontal areas. In aMCI patients, encoding impairment appears specifically related to atrophy of the CA1 hippocampal subfield, consistent with the predominance of encoding deficits and CA1 atrophy in aMCI. In contrast, episodic retrieval deficits seem to be underlain by more distributed tissue losses, consistent with a disruption of a hippocampo-parieto-frontal network.

Shift in brain metabolism in late onset Alzheimer's disease: implications for biomarkers and therapeutic interventions

Alzheimer's is a neurodegenerative disease with a complex and progressive pathological phenotype characterized first by hypometabolism and impaired mitochondrial bioenergetics followed by pathological burden. Increasing evidence indicates an antecedent and potentially causal role of mitochondrial bioenergetic deficits and brain hypometabolism coupled with increased mitochondrial oxidative stress in AD pathogenesis. Compromised mitochondrial bioenergetics lead to over-production of and mitochondrial accumulation of β-amyloid, which is coupled with oxidative stress. Collectively, this results in a shift in brain metabolic profile from glucose-driven bioenergetics towards a compensatory, but less efficient, ketogenic pathway. We propose that the compensatory shift from a primarily aerobic glycolysis pathway to a ketogenic/fatty acid β-oxidation pathway eventually leads to white matter degeneration. The essential role of mitochondrial bioenergetics and the unique trajectory of compensatory metabolic adaptations in brain enable a bioenergetic-centric strategy for development of biomarkers. From a therapeutic perspective, this trajectory of alterations in brain metabolic capacity enables disease-stage specific strategies to target brain metabolism for disease prevention and treatment. A combination of nutraceutical and pharmaceutical interventions that enhance glucose-driven metabolic activity and potentiate mitochondrial bioenergetic function could prevent the antecedent decline in brain glucose metabolism, promote healthy aging and prevent AD. Alternatively, during the prodromal incipient phase of AD, sustained activation of ketogenic metabolic pathways coupled with supplementation of the alternative fuel source, ketone bodies, could sustain mitochondrial bioenergetic function to prevent or delay further progression of the disease.

Nuclear medicine imaging in dementia: a practical overview for hospitalists

Dementia is a clinical syndrome with diverse presentation, a challenging differential diagnosis, and time-sensitive therapy. The most common cause of dementia in patients aged > 65 years is Alzheimer's disease, which now affects 4 million people in the United States, but is often underrecognized, especially in the inpatient population. The hospitalist may have the opportunity to evaluate a patient's initial presentation of dementia. Addressing the inpatient's dementia symptoms can improve overall care and outcomes, so it is imperative that the hospitalist is abreast of recent developments in the dementia workup. The focus of this article is to overview how nuclear medicine imaging of the brain can aid in this process, with perfusion single-photon emission computed tomography (SPECT) and fludeoxyglucose F 18 ((18)F-FDG) positron emission tomography (PET) as the 2 most common modalities. Our discussion focuses on Alzheimer's disease, as this the most common etiology of dementia in patients aged > 65 years; however, we also touch on the other common neurodegenerative dementias (eg, dementia with Lewy bodies, vascular dementia, and frontotemporal dementia) for completeness. We begin with a summary of the most recent published guidelines for each of these neurodegenerative diseases, and then expand on the role that nuclear imaging plays in each. We provide a basic overview of the principles of these nuclear medicine techniques, and then illustrate findings in perfusion SPECT and (18)F-FDG PET for typical patterns of dementia, with emphasis on evidence regarding diagnostic accuracy of each modality, in comparison with accepted gold standards. Finally, we outline some future research topics within the field of nuclear medicine in dementia, including amyloid plaque imaging and dopamine transporter imaging.

Perfusion SPECT and FDG-PET

Both perfusion SPECT and FDG-PET provide images that closely reflect neuronal activity. There is a characteristic regional impairment in Alzheimer’s disease (AD) that involves mainly the temporo-parietal association cortices, mesial temporal structures and to a more variable degree also the frontal association cortex. This pattern of functional impairment can provide a biomarker for diagnosis of AD and other neurodegenerative dementias at the clinical stage of mild cognitive impairment, and for monitoring of progression. FDG-PET is quantitatively more accurate and thus better suited to multicenter studies than perfusion SPECT. Regional metabolic and blood flow changes are closely related to clinical symptoms, and most areas involved in these changes will also develop significant cortical atrophy. FDG-PET is complementary to amyloid PET, which targets a molecular marker that does not have a close relation to current symptoms. Current restrictions in the availability and cost of FDG-PET are being reduced, as oncological FDG-PET is being adopted as a standard clinical service in most countries. Limitations in the availability of trained staff should be overcome by training programs set up by professional organizations. Against the background of the development of new criteria for diagnosing AD before the onset of dementia, FDG-PET is expected to play an increasing role in diagnosing patients at an early stage of AD and in clinical trials of drugs aimed at preventing or delaying the onset of dementia.

An international perspective on advanced neuroimaging: cometh the hour or ivory tower?

Over the past five to ten years, neuroimaging capability for neurodegenerative diseases has made remarkable progress. However, debate remains as to the true clinical utility of these advanced and costly investigations. Not only is the place of these tests in diagnostic algorithms unclear, but the access to them varies both within and between countries. We sought to gather informed opinion from recognized leaders in the field who can combine both an academic and a clinical perspective on the use of neuroimaging in their own countries. Opinion is presented from Scotland, Argentina, the Czech Republic, France, the USA and Australia. The emerging consensus was one of ongoing caution. While in most countries there was a sense that the use of more advanced imaging techniques was growing, their hour has not yet cometh. However, these techniques, rather than falling from the Ivory Tower, should descend slowly step by step onto fertile and receptive clinics from where better clinical guidelines will emerge.

The default mode network in healthy aging and Alzheimer's disease

In the past decade, a “default mode network” (DMN) has been highlighted in neuroimaging studies as a set of brain regions showing increased activity in task-free state compared to cognitively demanding task, and synchronized activity at rest. Changes within this network have been described in healthy aging as well as in Alzheimer's disease (AD) and populations at risk for AD, that is, amnestic Mild Cognitive Impairment (aMCI) patients and APOE-ε4 carriers. This is of particular interest in the context of early diagnosis and more generally for our understanding of the physiopathological mechanisms of AD. This paper gives an overview of the anatomical and physiological characteristics of this network as well as its relationships with cognition, before focusing on changes in the DMN over normal aging and Alzheimer's disease. While perturbations of the DMN have been consistently reported, especially within the posterior cingulate, further studies are needed to understand their clinical implication.

Disruption of limbic white matter pathways in mild cognitive impairment and Alzheimer's disease: a DTI/FDG-PET study

BACKGROUND

Alzheimer's disease (AD) and mild cognitive impairment (MCI) affect the limbic system, causing medial temporal lobe (MTL) atrophy and posterior cingulate cortex (PCC) hypometabolism. Additionally, diffusion tensor imaging (DTI) studies have demonstrated that MCI and AD involve alterations in cerebral white matter (WM) integrity.

OBJECTIVES

To test if (1) patients with MCI and AD exhibit decreases in the integrity of limbic WM pathways; (2) disconnection between PCC and MTL, manifested as disruption of the cingulum bundle, contributes to PCC hypometabolism during incipient AD.

METHODS

We measured fractional anisotropy (FA) and volume of the fornix and cingulum using DTI in 23 individuals with MCI, 21 with mild-to-moderate AD, and 16 normal control (NC) subjects. We also measured PCC metabolism using (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in AD and MCI patients.

RESULTS

Fornix FA and volume were reduced in MCI and AD to a similar extent. Descending cingulum FA was reduced in AD while volume was reduced in MCI and even more so in AD. Both FA and volume of the fornix and descending cingulum reliably discriminated between NC and AD. Fornix FA and descending cingulum volume also reliably discriminated between NC and MCI. Only descending cingulum volume reliably discriminated between MCI and AD. In the combined MCI-AD cohort, PCC metabolism directly correlated with both FA and volume of the descending cingulum.

CONCLUSIONS

Disruption of limbic WM pathways is evident during both MCI and AD. Disconnection of the PCC from MTL at the cingulum bundle contributes to PCC hypometabolism during incipient AD.

DTI and MR Volumetry of Hippocampus-PC/PCC Circuit: In Search of Early Micro- and Macrostructural Signs of Alzheimers's Disease

Hippocampal damage, by DTI or MR volumetry, and PET hypoperfusion of precuneus/posterior cingulate cortex (PC/PCC) were proposed as biomarkers of conversion from preclinical (MCI) to clinical stage of Alzheimer's disease (AD). This study evaluated structural damage, by DTI and MR volumetry, of hippocampi and tracts connecting hippocampus to PC/PCC (hipp-PC/PCC) in 10 AD, 10 MCI, and 18 healthy controls (CTRL). Normalized volumes, mean diffusivity (MD), and fractional anisotropy (FA) were obtained for grey matter (GM), white matter (WM), hippocampi, PC/PCC, and hipp-PC/PCC tracts. In hippocampi and hipp-PC/PCC tracts, decreased volumes and increased MD were found in AD versus CTRL (P < .001). The same results with lower significance (P < .05) were found in MCI versus CTRL. Verbal memory correlated (P < .05) in AD with left hippocampal and hipp-PC/PCC tract MD, and in MCI with FA of total WM. Both DTI and MR volumetry of hippocampi and hipp-PC/PCC tracts detect early signs of AD in MCI patients.

Visual personal familiarity in amnestic mild cognitive impairment

BACKGROUND

Patients with amnestic mild cognitive impairment are at high risk for developing Alzheimer's disease. Besides episodic memory dysfunction they show deficits in accessing contextual knowledge that further specifies a general concept or helps to identify an object or a person.

METHODOLOGY/PRINCIPAL FINDINGS

Using functional magnetic resonance imaging, we investigated the neural networks associated with the perception of personal familiar faces and places in patients with amnestic mild cognitive impairment and healthy control subjects. Irrespective of stimulus type, patients compared to control subjects showed lower activity in right prefrontal brain regions when perceiving personally familiar versus unfamiliar faces and places. Both groups did not show different neural activity when perceiving faces or places irrespective of familiarity.

CONCLUSIONS/SIGNIFICANCE

Our data highlight changes in a frontal cortical network associated with knowledge-based personal familiarity among patients with amnestic mild cognitive impairment. These changes could contribute to deficits in social cognition and may reduce the patients' ability to transition from basic to complex situations and tasks.

Damage to the cingulum contributes to Alzheimer's disease pathophysiology by deafferentation mechanism

This study investigates the differential contribution of gray matter (GM) atrophy and deafferentation through white matter (WM) damage in the clinical progression of Alzheimer's disease (AD). Thirty-one patients with probable AD, 23 with amnestic mild cognitive impairment (a-MCI), and 14 healthy subjects underwent MRI scanning at 3T. Voxel-based morphometry was used to assess regional GM atrophy in AD and a-MCI patients. Diffusion tensor-MRI tractography was used to reconstruct the cingulum bilaterally, and to quantify, voxel-by-voxel, its fractional anisotropy (FA) and mean diffusivity (MD) (measures of microscopic WM integrity). Atrophy of the cinguli was also assessed by means of jacobian determinants (JD) of local transformations. In AD patients, four clusters of reduced GM were found nearby the cinguli, in the posterior (PCC) and anterior cingulate cortex, and in the hippocampal/parahippocampal areas. Widespread areas of reduced FA and increased MD were found in the cinguli of both, AD and a-MCI patients. A region of macroscopic atrophy was detectable in AD patients only. Strong associations were found between local GM densities in the four identified clusters, and measures of micro- and (to a lesser extent) macroscopic damage of patients' cinguli. Linear regression analyses revealed that MD in the cinguli predicts patients' measures of episodic memory in combination with GM density of hippocampal/parahippocampal areas, and measures of global cognition in combination with GM density of the PCC. This study indicates that brain deafferentation though the cingulum is likely to play a remarkable role in progressive development of cognitive impairment in AD.

Mild cognitive impairment: baseline and longitudinal structural MR imaging measures improve predictive prognosis

PURPOSE

To assess whether single-time-point and longitudinal volumetric magnetic resonance (MR) imaging measures provide predictive prognostic information in patients with amnestic mild cognitive impairment (MCI).

MATERIALS AND METHODS

This study was conducted with institutional review board approval and in compliance with HIPAA regulations. Written informed consent was obtained from all participants or the participants' legal guardians. Cross-validated discriminant analyses of MR imaging measures were performed to differentiate 164 Alzheimer disease (AD) cases from 203 healthy control cases. Separate analyses were performed by using data from MR images obtained at one time point or by combining single-time-point measures with 1-year change measures. Resulting discriminant functions were applied to 317 MCI cases to derive individual patient risk scores. Risk of conversion to AD was estimated as a continuous function of risk score percentile. Kaplan-Meier survival curves were computed for risk score quartiles. Odds ratios (ORs) for the conversion to AD were computed between the highest and lowest quartile scores.

RESULTS

Individualized risk estimates from baseline MR examinations indicated that the 1-year risk of conversion to AD ranged from 3% to 40% (average group risk, 17%; OR, 7.2 for highest vs lowest score quartiles). Including measures of 1-year change in global and regional volumes significantly improved risk estimates (P = 001), with the risk of conversion to AD in the subsequent year ranging from 3% to 69% (average group risk, 27%; OR, 12.0 for highest vs lowest score quartiles).

CONCLUSION

Relative to the risk of conversion to AD conferred by the clinical diagnosis of MCI alone, MR imaging measures yield substantially more informative patient-specific risk estimates. Such predictive prognostic information will be critical if disease-modifying therapies become available.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101975/-/DC1.

[Neuroimaging Alzheimer's disease: early diagnosis, monitoring, and mechanism understanding]

Neuroimaging offers a promising tool for the priority goals of current researches in Alzheimer's disease (AD) including early diagnosis, monitoring the progression of the disease and understanding the underlying mechanisms. The brain profiles of atrophy and hypometabolism associated with AD are well known and they can be used as support for early diagnosis, although the accuracy of each of these biomarkers on its own is not sufficient. An increasing number of studies highlights the relevance of disconnection processes in the development and progression of AD. The recent development of PET tracers such as the Pittsburg compound (PiB) allowing to visualize in vivo one of the neuropathological lesions characterizing AD (i.e. beta-amyloid depositions) offers a unique opportunity to better understand the mechanisms underlying this multifaceted disease.

Independent contribution of temporal beta-amyloid deposition to memory decline in the pre-dementia phase of Alzheimer's disease

The relationship between β-amyloid deposition and memory deficits in early Alzheimer's disease is unresolved, as past studies show conflicting findings. The present study aims to determine the relative contribution of regional β-amyloid deposition, hippocampal atrophy and white matter integrity to episodic memory deficits in non-demented older individuals harbouring one of the characteristic hallmarks of Alzheimer's disease, i.e. with β-amyloid pathology. Understanding these relationships is critical for effective therapeutic development. Brain magnetic resonance imaging and [(11)C]Pittsburgh Compound B-positron emission tomography scans were obtained in 136 non-demented individuals aged over 60 years, including 93 healthy elderly and 43 patients with mild cognitive impairment. Voxel-based correlations were computed between a memory composite score and grey matter volume, white matter volume and β-amyloid deposition imaging datasets. Hierarchical linear regression analyses were then performed using values extracted in regions of most significant correlations to determine the relative contribution of each modality to memory deficits. All analyses were conducted pooling all groups together as well as within separate subgroups of cognitively normal elderly, patients with mild cognitive impairment and individuals with high versus low neocortical β-amyloid. Brain areas of highest correlation with episodic memory deficits were the hippocampi for grey matter volume, the perforant path for white matter volume and the temporal neocortex for β-amyloid deposition. When considering these three variables together, only hippocampal volume and temporal β-amyloid deposition provided independent contributions to memory deficits. In contrast to global β-amyloid deposition, temporal β-amyloid deposition was still related to memory independently from hippocampal atrophy within subgroups of cognitively normal elderly, patients with mild cognitive impairment or cases with high neocortical β-amyloid. In the pre-dementia stage of Alzheimer's disease, subtle episodic memory impairment is related to β-amyloid deposition, especially in the temporal neocortex, and independently from hippocampal atrophy, suggesting that both factors should be independently targeted in therapeutic trials aimed at reducing cognitive decline.

Quantitative structural MRI for early detection of Alzheimer's disease

Alzheimer's disease (AD) is a common progressive neurodegenerative disorder that is not currently diagnosed until a patient reaches the stage of dementia. There is a pressing need to identify AD at an earlier stage, so that treatment, when available, can begin early. Quantitative structural MRI is sensitive to the neurodegeneration that occurs in mild and preclinical AD, and is predictive of decline to dementia in individuals with mild cognitive impairment. Objective evidence of ongoing brain atrophy will be critical for risk/benefit decisions once potentially aggressive, disease-modifying treatments become available. Recent advances have paved the way for the use of quantitative structural MRI in clinical practice, and initial clinical use has been promising. However, further experience with these measures in the relatively unselected patient populations seen in clinical practice is needed to complete translation of the recent enormous advances in scientific knowledge of AD into the clinical realm.

Early-onset dysfunction of retrosplenial cortex precedes overt amyloid plaque formation in Tg2576 mice

A mouse model of amyloid pathology was used to first examine using a cross sectional design changes in retrosplenial cortex activity in transgenic mice aged 5, 11, 17, and 23 months. Attention focused on: (1) overt amyloid labeled with β-amyloid((1-42)) and Congo Red staining, (2) metabolic function assessed by the enzyme, cytochrome oxidase, and (3) neuronal activity as assessed indirectly by the immediate-early gene (IEG), c-Fos. Changes in cytochrome oxidase and c-Fos activity were observed in the retrosplenial cortex in Tg2576 mice as early as 5 months of age, long before evidence of plaque formation. Subsequent analyses concentrating on this early dysfunction revealed at 5 months pervasive, amyloid precursor protein (APP)-derived peptide accumulation in the retrosplenial cortex and selective afferents (anterior thalamus, hippocampus), which was associated with the observed c-Fos hyporeactivity. These findings indicate that retrosplenial cortex dysfunction occurs during early stages of amyloid production in Tg2576 mice and may contribute to cognitive dysfunction.

Open-label study of the short-term effects of memantine on FDG-PET in frontotemporal dementia

BACKGROUND

Memantine has shown effects on cortical metabolism in Alzheimer's disease (AD), and the mechanism of action may not be specific to AD alone. We hypothesized that participants with frontotemporal dementia taking memantine would show an increased cortical metabolic activity in frontal regions, temporal regions, or in salience network hubs.

METHODS

Sixteen participants with behavioral or language variant frontotemporal dementia syndromes (FTD) were recruited from tertiary FTD clinics and treated with memantine hydrochloride 10 mg twice daily in this fixed-dose, open-label pilot study. The primary endpoint was enhancement of cortical metabolic activity after 7-8 weeks of treatment. Secondary endpoints were measures of mood and behavior disturbance, frontal executive function, and motor disturbance.

RESULTS

Voxel-wise parametric image analysis of positron emission tomography (PET) data from seven behavioral variant FTD patients, eight semantic dementia patients, and one progressive nonfluent aphasia patient, of mean age 64.3 years, mean duration of illness 4.25 years, and baseline mean sum of boxes Clinical Dementia Rating score 6.59, revealed an increase in [(18)F]-fluorodeoxyglucose (FDG) normalized metabolic activity in bilateral insulae and the left orbitofrontal cortex (P < 0.01). The increase on FDG-PET did not correlate with changes on behavioral inventories. Post hoc analysis indicated that semantic dementia participants drove this finding.

CONCLUSION

This open-label clinical PET study suggests that memantine induces an increase in metabolism in the salience network in FTD. A placebo-controlled follow-up study is warranted.

Gray matter atrophy rate as a marker of disease progression in AD

Global gray matter (GM) atrophy rates were quantified from magnetic resonance imaging (MRI) over 6- and 12-month intervals in 37 patients with Alzheimer's disease (AD) and 19 controls using: (1) nonlinear registration and integration of Jacobian values, and (2) segmentation and subtraction of serial GM volumes. Sample sizes required to power treatment trials using global GM atrophy rate as an outcome measure were estimated and compared between the 2 techniques, and to global brain atrophy measures quantified using the boundary shift integral (brain boundary shift integral; BBSI) and structural image evaluation, using normalization, of atrophy (SIENA). Increased GM atrophy rates (approximately 2% per year) were observed in patients compared with controls. Although mean atrophy rates provided by Jacobian integration were smaller than those from segmentation and subtraction of GM volumes, measurement variance was reduced. The number of patients required per treatment arm to detect a 20% reduction in GM atrophy rate over a 12-month follow-up (90% power) was 202 (95% confidence interval [CI], 118–423) using Jacobian integration and 2047 (95% CI 271 to > 10 000) using segmentation and subtraction. Comparable sample sizes for whole brain atrophy were 240 (95% CI, 142–469) using the BBSI and 196 (95% CI, 110–425) using SIENA. Jacobian integration could be useful for measuring GM atrophy rate in Alzheimer's disease as a marker of disease progression and treatment efficacy.