Serial MRI and CSF biomarkers in normal aging, MCI, and AD

OBJECTIVE

To compare the annual change in MRI and CSF biomarkers in cognitively normal (CN), amnestic mild cognitive impairment (aMCI), and Alzheimer disease (AD). Comparisons were based on intergroup discrimination, correlation with concurrent cognitive/functional changes, relationships to APOE genotype, and sample sizes for clinical trials.

METHODS

We used data from the Alzheimer's Disease Neuroimaging Initiative study consisting of CN, aMCI, and AD cohorts with both baseline and 12-month follow-up CSF and MRI. The annual change in CSF (total-tau [t-tau], Abeta(1-42)) and MRI (change in ventricular volume) was obtained in 312 subjects (92 CN, 149 aMCI, 71 AD).

RESULTS

There was no significant average annual change in either CSF biomarker in any clinical group except t-tau in CN; moreover, the annual change did not differ by clinical group in pairwise comparisons. In contrast, annual increase in ventricular volume increased in the following order, AD > aMCI > CN, and differences were significant between all clinical groups in pairwise comparisons. Ventricular volume increase correlated with concurrent worsening on cognitive/functional indices in aMCI and AD whereas evidence of a similar correlation with change in CSF measures was unclear. The annual changes in MRI differed by APOE epsilon4 status overall and among aMCI while annual changes in CSF biomarkers did not. Estimated sample sizes for clinical trials are notably less for MRI than the CSF or clinical measures.

CONCLUSIONS

Unlike the CSF biomarkers evaluated, changes in serial structural MRI are correlated with concurrent change on general cognitive and functional indices in impaired subjects, track with clinical disease stage, and are influenced by APOE genotype.

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.

Gray and white matter water diffusion in the syndromic variants of frontotemporal dementia

OBJECTIVE

To use diffusion tensor imaging (DTI) to assess gray matter and white matter tract diffusion in behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SMD), and progressive nonfluent aphasia (PNFA).

METHODS

This was a case-control study where 16 subjects with bvFTD, 7 with PNFA, and 4 with SMD were identified and matched by age and gender to 19 controls. All subjects had 3-T head MRI with a DTI sequence with diffusion encoding in 21 directions. Gray matter mean diffusivity (MD) was assessed using a region-of-interest (ROI) and voxel-level approach, and voxel-based morphometry was used to assess patterns of gray matter loss. White matter tract diffusivity (fractional anisotropy and radial diffusivity) was assessed by placing ROIs on tracts of interest.

RESULTS

In bvFTD, increased gray matter MD and gray matter loss were identified bilaterally throughout frontal and temporal lobes, with abnormal diffusivity observed in white matter tracts that connect to these regions. In SMD, gray matter loss and increased MD were identified predominantly in the left temporal lobe, with tract abnormalities observed in the inferior longitudinal fasciculus and uncinate fasciculus. In PNFA, gray matter loss and increased MD were observed in left inferior frontal lobe, insula, and supplemental motor area, with tract abnormalities observed in the superior longitudinal fasciculus.

CONCLUSIONS

The diffusivity of gray matter is increased in regions that are atrophic in frontotemporal dementia, suggesting disruption of the cytoarchitecture of remaining tissue. Furthermore, damage was identified in white matter tracts that interconnect these regions, supporting the hypothesis that these diseases involve different and specific brain networks.

Effects of age on the glucose metabolic changes in mild cognitive impairment

BACKGROUND AND PURPOSE

Decreased glucose metabolism in the temporal and parietal lobes on FDG-PET is recognized as an early imaging marker for the AD pathology. Our objective was to investigate the effects of age on FDG-PET findings in aMCI.

MATERIALS AND METHODS

Twenty-five patients with aMCI at 55-86 years of age (median = 73 years) and 25 age- and sex-matched CN subjects underwent FDG-PET. SPM5 was used to compare the FDG uptake in patients in aMCI-old (>73 years) and aMCI-young (<or=73 years) groups with CN subjects. The findings in the aMCI-old patients were independently validated in a separate cohort of 10 aMCI and 13 CN subjects older than 73 years of age.

RESULTS

The pattern of decreased glucose metabolism and gray matter atrophy in the medial temporal, posterior cingulate, precuneus, lateral parietal, and temporal lobes in aMCI-young subjects was consistent with the typical pattern observed in AD. The pattern of glucose metabolic changes in aMCI-old subjects was different, predominantly involving the frontal lobes and the left parietal lobe. Gray matter atrophy in aMCI-old subjects was less pronounced than that in the aMCI-young subjects, involving the hippocampus and the basal forebrain in both hemispheres

CONCLUSIONS

Pathologic heterogeneity may be underlying the absence of AD-like glucose metabolic changes in older compared with younger patients with aMCI. This may be an important consideration for the clinical use of temporoparietal hypometabolism on FDG-PET as a marker for early diagnosis of AD in aMCI.

Two distinct subtypes of right temporal variant frontotemporal dementia

BACKGROUND

Right temporal frontotemporal dementia (FTD) is an anatomic variant of FTD associated with relatively distinct behavioral and cognitive symptoms. We aimed to determine whether right temporal FTD is a homogeneous clinical, imaging, and pathologic/genetic entity.

METHODS

In this case-control study, 101 subjects with FTD were identified. Atlas-based parcellation generated temporal, frontal, and parietal grey matter volumes which were used to identify subjects with a right temporal dominant atrophy pattern. Clinical, neuropsychological, genetic, and neuropathologic features were reviewed. The subjects with right temporal FTD were grouped by initial clinical diagnosis and voxel-based morphometry was used to assess grey matter loss in the different groups, compared to controls, and each other.

RESULTS

We identified 20 subjects with right temporal FTD. Twelve had been initially diagnosed with behavioral variant FTD (bvFTD), and the other 8 with semantic dementia (SMD). Personality change and inappropriate behaviors were more frequent in the bvFTD group, while prosopagnosia, word-finding difficulties, comprehension problems, and topographagnosia were more frequent in the SMD group. The bvFTD group showed greater loss in frontal lobes than the SMD group. The SMD group showed greater fusiform loss than the bvFTD group. All 8 bvFTD subjects with pathologic/genetic diagnosis showed abnormalities in tau protein (7 with tau mutations), while all three SMD subjects with pathology showed abnormalities in TDP-43 (p = 0.006).

CONCLUSIONS

We have identified 2 subtypes of right temporal variant frontotemporal dementia (FTD) allowing further differentiation of FTD subjects with underlying tau pathology from those with TDP-43 pathology.

Atrophy patterns in IVS10+16, IVS10+3, N279K, S305N, P301L, and V337M MAPT mutations

OBJECTIVE

To use a case-control study to assess and compare patterns of gray matter loss across groups of subjects with different mutations in the microtubule-associated protein tau (MAPT) gene.

METHODS

We identified all subjects from Mayo Clinic, Rochester, Minnesota, that screened positive for mutations in MAPT and had a head MRI (n = 22). Voxel-based morphometry was used to assess patterns of gray matter atrophy in groups of subjects with the IVS10+16, IVS10+3, N279K, S305N, P301L, and V337M mutations compared with age- and sex-matched controls.

RESULTS

All MAPT groups showed gray matter loss in the anterior temporal lobes, with varying degrees of involvement of the frontal and parietal lobes. Within the temporal lobe, the subjects with IVS10+16, IVS10+3, N279K, and S305N mutations (mutations that influence the alternative splicing of tau pre-messenger RNA) all showed gray matter loss focused on the medial temporal lobes. In contrast to these groups, the subjects with P301L or V337M mutations (mutations that affect the structure of the tau protein) both showed gray matter loss focused on the lateral temporal lobes, with a relative sparing of the medial temporal lobe.

CONCLUSION

There seem to be differences in patterns of temporal lobe atrophy across the MAPT mutations, which may aid in the differentiation of the different mutation carriers. Furthermore, there seems to be a possible association between mutation function and pattern of temporal lobe atrophy.

MRI and CSF biomarkers in normal, MCI, and AD subjects: diagnostic discrimination and cognitive correlations

OBJECTIVE

To assess the correlations of both MRI and CSF biomarkers with clinical diagnosis and with cognitive performance in cognitively normal (CN) subjects and patients with amnestic mild cognitive impairment (aMCI) and Alzheimer disease (AD).

METHODS

This is a cross-sectional study with data from the Alzheimer's Disease Neuroimaging Initiative, which consists of CN subjects, subjects with aMCI, and subjects with AD with both CSF and MRI. Baseline CSF (t-tau, Abeta(1-42), and p-tau(181P)) and MRI scans were obtained in 399 subjects (109 CN, 192 aMCI, 98 AD). Structural Abnormality Index (STAND) scores, which reflect the degree of AD-like anatomic features on MRI, were computed for each subject.

RESULTS

We found no significant correlation between CSF biomarkers and cognitive scores in any of the 3 clinical groups individually. Conversely, STAND scores correlated with both Clinical Dementia Rating-sum of boxes and Mini-Mental State Examination in aMCI and AD (p < or = 0.01). While STAND and all CSF biomarkers were predictors of clinical group membership (CN, aMCI, or AD) univariately (p < 0.001), STAND was more predictive than CSF both univariately and in combined models.

CONCLUSIONS

CSF and MRI biomarkers independently contribute to intergroup diagnostic discrimination and the combination of CSF and MRI provides better prediction than either source of data alone. However, MRI provides greater power to effect cross-sectional groupwise discrimination and better correlation with general cognition and functional status cross-sectionally. We therefore conclude that although MRI and CSF provide complementary information, MRI reflects clinically defined disease stage better than the CSF biomarkers tested.

MRI and CSF biomarkers in normal, MCI, and AD subjects: predicting future clinical change

OBJECTIVE

To investigate the relationship between baseline MRI and CSF biomarkers and subsequent change in continuous measures of cognitive and functional abilities in cognitively normal (CN) subjects and patients with amnestic mild cognitive impairment (aMCI) and Alzheimer disease (AD) and to examine the ability of these biomarkers to predict time to conversion from aMCI to AD.

METHODS

Data from the Alzheimer's Disease Neuroimaging Initiative, which consists of CN, aMCI, and AD cohorts with both CSF and MRI, were used. Baseline CSF (t-tau, Abeta(1-42), and p-tau(181P)) and MRI scans were obtained in 399 subjects (109 CN, 192 aMCI, 98 AD). Structural Abnormality Index (STAND) scores, which reflect the degree of AD-like features in MRI, were computed for each subject.

RESULTS

Change on continuous measures of cognitive and functional performance was modeled as average Clinical Dementia Rating-sum of boxes and Mini-Mental State Examination scores over a 2-year period. STAND was a better predictor of subsequent cognitive/functional change than CSF biomarkers. Single-predictor Cox proportional hazard models for time to conversion from aMCI to AD showed that STAND and log (t-tau/Abeta(1-42)) were both predictive of future conversion. The age-adjusted hazard ratio for an interquartile change (95% confidence interval) of STAND was 2.6 (1.7, 4.2) and log (t-tau/Abeta(1-42)) was 2.0 (1.1, 3.4). Both MRI and CSF provided information about future cognitive change even after adjusting for baseline cognitive performance.

CONCLUSIONS

MRI and CSF provide complimentary predictive information about time to conversion from amnestic mild cognitive impairment to Alzheimer disease and combination of the 2 provides better prediction than either source alone. However, we found that MRI was a slightly better predictor of future clinical/functional decline than the CSF biomarkers tested.

Brain and ventricular volumetric changes in frontotemporal lobar degeneration over 1 year

BACKGROUND

Measurement of volumetric changes with MR might be a useful surrogate endpoint for clinical trials in frontotemporal lobar degeneration (FTLD). Because there is only limited longitudinal imaging data currently available, we measured the rate of change over 1 year of whole brain volume (WBV) and ventricular volume (VV) in patients with FTLD.

METHODS

Subjects with an FTLD cognitive syndrome were recruited from five centers using standard clinical diagnostic criteria for behavioral variant frontotemporal dementia (bvFTD), progressive nonfluent aphasia (PNFA), semantic dementia (SMD), and progressive logopenic aphasia. Structural brain imaging, using three-dimensional T1-weighted sequences at 1.5 teslas, and cognitive, behavioral, and functional assessments were performed at baseline and approximately 1 year later. The boundary shift integral algorithm was used to determine change in WBV and VV.

RESULTS

There were 76 patients (mean age 64 years; 41 men and 35 women) who had usable baseline and annual scans. The group-wise annualized change was -1.62% (SD 1.03, range +0.69 to -3.6) for WBV and 11.6% (SD 5.9, range -1.3 to 23.9) for VV. Rates of change were similar among bvFTD, PNFA, and SMD groups. Longitudinal changes in WBV and VV were correlated with decline on clinical global and cognitive measures.

CONCLUSIONS

Multicenter, serial measurements of whole brain volume (WBV) and ventricular volume (VV) from magnetic resonance scans were feasible in patients with frontotemporal lobar degeneration (FTLD). Using WBV or VV as outcome measures would require recruiting (at 80% power) 139 or 55 subjects per group to detect a small (25%) or medium-sized (40%) effect in a randomized, placebo-controlled trial of a putative agent for FTLD.

Risk of dementia in MCI: combined effect of cerebrovascular disease, volumetric MRI, and 1H MRS

OBJECTIVE

To investigate the combined ability of hippocampal volumes, 1H magnetic resonance spectroscopy (MRS) metabolites, and cerebrovascular disease to predict the risk of progression to dementia in mild cognitive impairment (MCI).

METHODS

We identified 151 consecutively recruited subjects with MCI from the Mayo Clinic Alzheimer's Disease Research Center and Patient Registry who underwent MRI and 1H MRS studies at baseline and were followed up with approximately annual clinical examinations. A multivariable proportional hazards model that considered all imaging predictors simultaneously was used to determine whether hippocampal volumes, posterior cingulate gyrus 1H MRS metabolites, white matter hyperintensity load, and presence of cortical and subcortical infarctions are complementary in predicting the risk of progression from MCI to dementia.

RESULTS

Seventy-five subjects with MCI progressed to dementia by last follow-up. The model that best predicted progression to dementia included age, sex, hippocampal volumes, N-acetylaspartate (NAA)/creatine (Cr) on 1H MRS, and cortical infarctions. Based on age- and sex-adjusted Kaplan-Meier plots, we estimated that by 3 years, 26% of the MCI patients with normal hippocampal volumes, NAA/Cr ratios >1 SD, and no cortical infarctions will progress to dementia, compared with 78% of the MCI patients with hippocampal atrophy, low NAA/Cr (< or =1 SD), and cortical infarction.

CONCLUSIONS

Multiple magnetic resonance (MR) markers of underlying dementia pathologies improve the ability to identify patients with prodromal dementia over a single MR marker, supporting the concept that individuals with multiple brain pathologies have increased odds of dementia compared with individuals with a single pathology.

Voxel-based morphometry patterns of atrophy in FTLD with mutations in MAPT or PGRN

OBJECTIVE

To compare patterns of gray matter loss in subjects with mutations in the progranulin (PGRN) gene to subjects with mutations in the microtubule-associated protein tau (MAPT) gene.

METHODS

We identified all subjects seen at the Mayo Clinic, Rochester, MN, who had screened positive for mutations in PGRN or MAPT and had a head MRI. Twelve cases with mutations in the PGRN gene were matched by time from disease onset to scan to 12 subjects with mutations in the MAPT gene. Voxel-based morphometry was used to assess patterns of gray matter loss in the PGRN and MAPT groups compared to a control cohort, and compared to each other. MAPT subjects were younger than the PGRN subjects; therefore, each group was also compared to a specific age-matched control group.

RESULTS

Both PGRN and MAPT groups showed gray matter loss in frontal, temporal, and parietal lobes compared to controls, although loss was predominantly identified in posterior temporal and parietal lobes in PGRN and anteromedial temporal lobes in MAPT. The MAPT group had greater loss compared to healthy subjects of the same age than the PGRN subjects when compared to healthy subjects of the same age. The MAPT subjects showed greater gray matter loss in the medial temporal lobes, insula, and putamen than the PGRN subjects.

CONCLUSION

These results increase understanding of the biology of these disorders and suggest that patterns of atrophy on MRI may be useful to aid in the differentiation of groups of PGRN and MAPT mutation carriers.

Surrogate consent for dementia research: a national survey of older Americans

BACKGROUND

Research in novel therapies for Alzheimer disease (AD) relies on persons with AD as research subjects. Because AD impairs decisional capacity, informed consent often must come from surrogates, usually close family members. But policies for surrogate consent for research remain unsettled after decades of debate.

METHODS

We designed a survey module for a random subsample (n = 1,515) of the 2006 wave of the Health and Retirement Study, a biennial survey of a nationally representative sample of Americans aged 51 and older. The participants answered questions regarding one of four randomly assigned surrogate-based research (SBR) scenarios: lumbar puncture study, drug randomized control study, vaccine study, and gene transfer study. Each participant answered three questions: whether our society should allow family surrogate consent, whether one would want to participate in the research, and whether one would allow one's surrogate some or complete leeway to override stated personal preferences.

RESULTS

Most respondents stated that our society should allow family surrogate consent for SBR (67.5% to 82.5%, depending on the scenario) and would themselves want to participate in SBR (57.4% to 79.7%). Most would also grant some or complete leeway to their surrogates (54.8% to 66.8%), but this was true mainly of those willing to participate. There was a trend toward lower willingness to participate in SBR among those from ethnic or racial minority groups.

CONCLUSIONS

Family surrogate consent-based dementia research is broadly supported by older Americans. Willingness to allow leeway to future surrogates needs to be studied further for its ethical significance for surrogate-based research policy.

The anatomic correlate of prosopagnosia in semantic dementia

OBJECTIVE

To determine the anatomic correlate of prosopagnosia in subjects with semantic dementia.

METHODS

We identified all subjects who had been evaluated by an experienced behavioral neurologist, met criteria for semantic dementia, and had completed a volumetric head MRI scan. In all subjects, historical records were reviewed and subjects in which the presence (n = 15) or absence (n = 12) of prosopagnosia was specifically ascertained by the neurologist were identified. Voxel-based morphometry was used to assess patterns of gray matter atrophy in subjects with and without prosopagnosia compared to a group of age and gender-matched normal controls, and compared to each other.

RESULTS

Compared to controls, both groups showed prominent temporal lobe volume loss. Those with prosopagnosia showed bilateral loss but with greater involvement of the right temporal lobe, while those without prosopagnosia showed predominantly left anterior temporal lobe loss. On direct comparison, subjects with prosopagnosia showed greater loss predominantly in the right amygdala, hippocampus, fusiform gyrus, and anterior temporal pole than those without prosopagnosia. No regions were involved to a greater degree in those without prosopagnosia, compared to those with prosopagnosia.

CONCLUSIONS

Prosopagnosia appears to be associated with volume loss of the right temporal lobe, particularly medial temporal lobe, fusiform gyrus, and anterior temporal pole, although in semantic dementia it is occurring in the context of bilateral temporal lobe volume loss.

MRI correlates of neurofibrillary tangle pathology at autopsy: a voxel-based morphometry study

BACKGROUND

Neurofibrillary tangles (NFTs), composed of hyperphosphorylated tau proteins, are one of the pathologic hallmarks of Alzheimer disease (AD). We aimed to determine whether patterns of gray matter atrophy from antemortem MRI correlate with Braak staging of NFT pathology.

METHODS

Eighty-three subjects with Braak stage III through VI, a pathologic diagnosis of low- to high-probability AD, and MRI within 4 years of death were identified. Voxel-based morphometry assessed gray matter atrophy in each Braak stage compared with 20 pathologic control subjects (Braak stages 0 through II).

RESULTS

In pairwise comparisons with Braak stages 0 through II, a graded response was observed across Braak stages V and VI, with more severe and widespread loss identified at Braak stage VI. No regions of loss were identified in Braak stage III or IV compared with Braak stages 0 through II. The lack of findings in Braak stages III and IV could be because Braak stage is based on the presence of any NFT pathology regardless of severity. Actual NFT burden may vary by Braak stage. Therefore, tau burden was assessed in subjects with Braak stages 0 through IV. Those with high tau burden showed greater gray matter loss in medial and lateral temporal lobes than those with low tau burden.

CONCLUSIONS

Patterns of gray matter loss are associated with neurofibrillary tangle (NFT) pathology, specifically with NFT burden at Braak stages III and IV and with Braak stage itself at higher stages. This validates three-dimensional patterns of atrophy on MRI as an approximate in vivo surrogate indicator of the full brain topographic representation of the neurodegenerative aspect of Alzheimer disease pathology.