Extent and distribution of white matter hyperintensities in normal aging, MCI, and AD.

OBJECTIVE: To analyze the extent and spatial distribution of white matter hyperintensities (WMH) in brain regions from cognitively normal older individuals (CN) and patients with mild cognitive impairment (MCI) and Alzheimer disease (AD). METHODS: We studied 26 mild AD, 28 MCI, and 33 CN. MRI analysis included quantification of WMH volume, nonlinear mapping onto a common anatomic image, and spatial localization of each WMH voxel to create an anatomically precise frequency distribution map. Areas of greatest frequency of WMH from the WMH composite map were used to identify 10 anatomic regions involving periventricular areas and the corpus callosum (CC) for group comparisons. RESULTS: Total WMH volumes were associated with age, extent of concurrent vascular risk factors, and diagnosis. After correcting for age, total WMH volumes remained significantly associated with diagnosis and extent of vascular risk. Regional WMH analyses revealed significant differences in WMH across regions that also differed significantly according to diagnosis. In post-hoc analyses, significant differences were seen between CN and AD in posterior periventricular regions and the splenium of the CC. MCI subjects had intermediate values at all regions. Repeated measures analysis including vascular risk factors in the model found a significant relationship between periventricular WMH and vascular risk that differed by region, but regional differences according to diagnosis remained significant and there was no interaction between diagnosis and vascular risk. CONCLUSIONS: Differences in white matter hyperintensities (WMH) associated with increasing cognitive impairment appear related to both extent and spatial location. Multiple regression analysis of regional WMH, vascular risk factors, and diagnosis suggest that these spatial differences may result from the additive effects of vascular and degenerative injury. Posterior periventricular and corpus callosum extension of WMH associated with mild cognitive impairment and Alzheimer disease indicate involvement of strategic white matter bundles that may contribute to the cognitive deficits seen with these syndromes.

Longitudinal volumetric MRI change and rate of cognitive decline.

OBJECTIVE: To examine how baseline and change of volumetric MRI relate to cognitive decline in older individuals. BACKGROUND: Memory is associated with hippocampal integrity, whereas executive function has been linked to impaired frontal lobe function. Previous studies have shown that hippocampal and cortical atrophy are more strongly related to cognition than are measures of subcortical cerebrovascular disease (CVD). The authors hypothesized that memory (MEM) decline would be related to change in hippocampal volume (HC), whereas decline in executive function (EXEC) would be related to change of cortical gray matter volume (CGM) and measures of subcortical CVD. METHODS: Subjects from a multicenter study (n = 103) included cognitively normal, mildly impaired, and demented cases with and without subcortical lacunes. All had longitudinal cognitive evaluation (mean = 4.8 years) and two or more MRI scans at least one year apart (mean = 3.4 years). MRI measures included HC, CGM, total lacune volume (LAC), and white matter hyperintensity volume (WMH). Random effects modeling of longitudinal data assessed effects of MRI baseline and MRI change on baseline and change of psychometrically matched measures of MEM and EXEC. RESULTS: Change in MEM was related to HC baseline and HC change. Change in EXEC was related to baseline CGM and to change in CGM, HC, and LAC. Results were unchanged when demented cases were excluded. WMH was not associated with change in MEM or EXEC independent of HC, CGM, and LAC. CONCLUSION: Hippocampal volume was the primary determinant of memory decline, whereas executive function (EXEC) decline was related to multiple brain components. Results support a hypothesis that MEM decline is strongly influenced by Alzheimer disease (AD), whereas EXEC decline may be complexly determined by cerebrovascular disease and AD.

White matter lesions impair frontal lobe function regardless of their location.

OBJECTIVE: To analyze the effect of white matter lesions in different brain regions on regional cortical glucose metabolism, regional cortical atrophy, and cognitive function in a sample with a broad range of cerebrovascular disease and cognitive function. METHODS: Subjects (n = 78) were recruited for a study of subcortical ischemic vascular disease (SIVD) and Alzheimer disease (AD) contributions to dementia. A new method was developed to define volumes of interest from high-resolution three-dimensional T1-weighted MR images. Volumetric measures of MRI segmented white matter signal hyperintensities (WMH) in five different brain regions were related to regional PET glucose metabolism (rCMRglc) in cerebral cortex, MRI measures of regional cortical atrophy, and neuropsychological assessment of executive and memory function. RESULTS: WMH was significantly higher in the prefrontal region compared to the other brain regions. In all subjects, higher frontal and parietal WMH were associated with reduced frontal rCMRglc, whereas occipitotemporal WMH was only marginally associated with frontal rCMRglc. These associations were stronger and more widely distributed in nondemented subjects where reduced frontal rCMRglc was correlated with WMH for all regions measured. In contrast, there was no relationship between WMH in any brain region and rCMRglc in either parietal or occipitotemporal regions. WMHs in all brain regions were associated with low executive scores in nondemented subjects. CONCLUSIONS: The frontal lobes are most severely affected by SIVD. WMHs are more abundant in the frontal region. Regardless of where in the brain these WMHs are located, they are associated with frontal hypometabolism and executive dysfunction.

Higher atrophy rate of entorhinal cortex than hippocampus in AD.

OBJECTIVES: To determine if atrophy rates were higher for entorhinal cortex (ERC) than for hippocampus in Alzheimer disease (AD), to determine the relationship between hippocampal atrophy rate and memory impairment, and to compare atrophy rates of ERC and hippocampus in differentiating between patients with AD and cognitively normal (CN) controls. METHODS: Twenty patients with AD and 25 CN subjects had MRI scans and clinical evaluations twice approximately 1.9 years apart. ERC volumes were measured manually and hippocampal volumes were measured semiautomatically on volumetric T1-weighted MR images. RESULTS: In AD, the atrophy rate of ERC (7.1 +/- 3.2%/year) was higher (p < 0.02) than that of hippocampus (5.9 +/- 2.4%/year). Furthermore, memory deficit in mild AD, measured with the Delayed List Verbal Recall test, correlated significantly with atrophy rates of both ERC (r = -0.61) and hippocampus (r = -0.59). Atrophy rates of ERC and hippocampus were comparable in differentiating between AD and CN. Using atrophy rates of ERC or hippocampus to detect a 20% treatment effect with 90% power (p < 0.05) would require about 100 completed patients per arm in a 2-year study. CONCLUSION: The finding in AD that the atrophy rate in the entorhinal cortex is higher than in the hippocampus is consistent with the view that AD pathology begins in the entorhinal cortex.

Different patterns of N-acetylaspartate loss in subcortical ischemic vascular dementia and AD.

OBJECTIVES: 1) To determine the regional pattern of reduced N-acetylaspartate (NAA) in subcortical ischemic vascular dementia (SIVD); 2) to explore the relationship between NAA reduction and subcortical vascular disease; and 3) to test if MR spectroscopic imaging (MRSI) in combination with structural MRI improves differentiation between SIVD and Alzheimer disease (AD). METHODS: Thirteen patients with SIVD (71 +/- 8 years old) and 43 patients with AD of comparable age and dementia severity were studied using MRSI and MRI. Patients were compared to 52 cognitively normal subjects with and without lacunes. RESULTS: Compared to controls, patients with SIVD had lower NAA by 18% (p < 0.001) in frontal cortex and by 27% (p < 0.003) in parietal cortex, but no significant NAA reduction in white matter and medial temporal lobe. Compared to patients with AD, patients with SIVD had lower NAA by 13% (p < 0.02) in frontal cortex and by 20% (p < 0.002) in left parietal cortex. Cortical NAA decreased in SIVD with increasing white matter lesions (r = 0.54, p < 0.02) and number of lacunes (r = 0.59, p < 0.02). Thalamic lacunes were associated with greater NAA reduction in frontal cortex than were lacunes outside the thalamus (p < 0.02) across groups, after adjusting for cognitive impairments. Adding parietal NAA to MRI-derived hippocampal atrophy improved separation between SIVD and AD (p = 0.02) from 79 to 89%. CONCLUSIONS: These results emphasize the importance of cortical dysfunction as a factor in SIVD and indicate a characteristic pattern of metabolite change that might serve as a basis for improved diagnosis.

Atrophy rates of entorhinal cortex in AD and normal aging.

OBJECTIVES: To explore the atrophy rate of entorhinal cortex (ERC) in AD and normal aging and assess the value of rate measurement of ERC atrophy for classifying subjects with AD from cognitively normal (CN) control subjects. METHODS: Twenty-one AD patients and 23 CN subjects had MRI scans and clinical evaluations twice within 1.8 +/- 0.6 years. ERC volumes were manually measured on volumetric T1-weighted MR images. RESULTS: Patients with AD had a greater annual percentage volume change of ERC than CN subjects on both sides (left: 6.8 +/- 4.3%/year for AD vs 1.4 +/- 2.5%/year for CN [F(1,42) = 25.6, p < 0.001]; right: 6.3 +/- 3.3%/year for AD vs 1.4 +/- 2.3%/year for CN [F(1,42) = 25.6, p < 0.001]). Furthermore, increased ERC atrophy rate was correlated (r = -0.56, p = 0.01) with decreased memory performance in AD. CN subjects had on average annual ERC atrophy rates greater than zero (p < 0.01). Baseline volume of ERC predicted atrophy rate of ERC (left: r = -0.53, p < 0.01; right: r = -0.42, p < 0.05) in CN subjects but not in AD subjects. Using ERC baseline volumes alone resulted in 77% overall correct classification (p < 0.01) between AD and CN subjects, with 76% sensitivity and 78% specificity and an area under receiver operator characteristic (ROC) curve of 0.83. Adding annual atrophy rate of ERC to the model accounted for most of the variance (p < 0.01), diminishing contributions from baseline volume and yielding 82% overall classification, with 76% sensitivity and 86% specificity and an area under the ROC curve of 0.93. CONCLUSION: ERC volume loss over time may be a better indicator for AD than cross-sectional measurements.

Volumetric MRI predicts rate of cognitive decline related to AD and cerebrovascular disease.

OBJECTIVE: To examine volumetric MRI correlates of longitudinal cognitive decline in normal aging, AD, and subcortical cerebrovascular brain injury (SCVBI). BACKGROUND: Previous cross-sectional studies examining the relationship between cognitive impairment and dementia have shown that hippocampal and cortical gray matter atrophy are the most important predictors of cognitive impairment, even in cases with SCVBI. The authors hypothesized that hippocampal and cortical gray matter volume also would best predict rate of cognitive decline in cases with and without SCVBI. METHODS: Subjects were recruited for a multicenter study of contributions to dementia of AD and SCVBI. The sample (n = 120) included cognitively normal, cognitively impaired, and demented cases with and without lacunes identified by MRI. Cases with cortical strokes were excluded. Average length of follow-up was 3.0 years. Measures of hippocampal volume, volume of cortical gray matter, presence of subcortical lacunes, and volume of white matter hyperintensity were derived from MRI. Random effects modeling of longitudinal data was used to assess effects of baseline MRI variables on longitudinal change in a measure of global cognitive ability. RESULTS: Cortical gray matter atrophy predicted cognitive decline regardless of whether lacunes were present. Hippocampal atrophy predicted decline only in those without lacunes. Neither lacunes nor white matter hyperintensity independently predicted decline. CONCLUSIONS: Results suggest that cortical atrophy is an index of disease severity in both AD and subcortical cerebrovascular brain injury and consequently predicts faster progression. Hippocampal volume may index disease severity and predict progression in AD. The absence of this effect in cases with lacunes suggests that this group is etiologically heterogeneous and is not composed simply of cases of AD with incidental stroke.

Utility of clinical criteria in differentiating frontotemporal lobar degeneration (FTLD) from AD.

OBJECTIVE: To assess the ability of the current diagnostic criteria for frontotemporal lobar degeneration (FTLD) to differentiate FTLD from AD. METHODS: Thirty cases with autopsy-proven FTLD and 30 cases of AD, matched for Mini-Mental State Examination score, were identified from the clinical databases of three dementia subspecialty centers, and their charts were reviewed for the presence of clinical features described in the current criteria for FTLD. The proportion of patients with each clinical feature at the first clinical presentation was compared across groups. RESULTS: A significantly larger proportion of patients with FTLD showed behavioral abnormalities, particularly social and personal conduct disorders and emotional blunting, than patients with AD. Few differences in language features were seen between the groups, and many of the language features detailed in the criteria were found in only a small proportion of patients. In both groups, many patients showed neuropsychological abnormalities, except for perceptual difficulties, which were present in many patients with AD but only in a few patients with FTLD. Extrapyramidal motor symptoms were more likely to be present in FTLD. Logistic regression revealed that five features-social conduct disorders, hyperorality, akinesia, absence of amnesia, and the absence of a perceptual disorder-correctly classified 93% of patients with FTLD and 97% of patients with AD. CONCLUSION: A combination of behavioral, neuropsychological, and physical findings is most useful in distinguishing FTLD from AD. Future studies should be directed at establishing more objective methods of identifying these clinical features.

Effects of subcortical ischemic vascular dementia and AD on entorhinal cortex and hippocampus.

OBJECTIVE: To determine the effects of subcortical ischemic vascular dementia (SIVD) and AD on entorhinal cortex (ERC) and hippocampus. METHODS: Thirty-eight cognitively normal subjects, 18 patients with SIVD, and 22 patients with AD were included. Volumes of ERC and hippocampus were manually measured based on MRI. Global cerebral changes of cortical gray matter, subcortical gray matter, white matter, sulcal CSF, ventricular CSF (vCSF), and white matter signal hyperintensities (WMSH) were assessed. RESULTS: Patients with SIVD had 21.7% (p < 0.01) smaller ERC and 18.2% (p < 0.01) smaller hippocampi than cognitively normal subjects and 24.4% (p < 0.01) larger ERC and 11.1% (p < 0.05) larger hippocampi than patients with AD. In addition, patients with SIVD had less cortical gray matter and white matter and more vCSF and WMSH (all p < 0.01) than cognitively normal subjects and more vCSF and WMSH (p < 0.01) than patients with AD. The volumes of ERC and hippocampus were positively correlated to similar extents (p < 0.01) in SIVD and AD. Cortical gray matter loss was positively correlated (p < 0.01) with hippocampal atrophy, but not with ERC atrophy, in SIVD and AD. Hippocampal volume alone could classify 82% of patients with SIVD from cognitively normal subjects and 63% of patients with SIVD from subjects with AD. Adding global cerebral changes to hippocampus substantially improved the classification to 96% between patients with SIVD and cognitively normal subjects and 83% between subjects with SIVD and those with AD, whereas adding ERC change to hippocampus did not significantly improve the discrimination. CONCLUSIONS: The entorhinal cortex and hippocampus are less affected by subcortical ischemic vascular dementia than by AD.

Homocysteine, vitamin B6, and vascular disease in AD patients.

BACKGROUND: Cerebrovascular disease is a cause of dementia and is associated with elevated plasma levels of homocysteine. Patients with AD tend to have unexplained elevations of homocysteine concentrations vs healthy control subjects. Vitamin B(6) status, a potential determinant of plasma homocysteine, has not been characterized in patients with AD. OBJECTIVE: To investigate plasma homocysteine, vitamin B(6) status, and the occurrence of vascular disease in patients with AD. METHODS: Forty-three patients with AD and 37 control subjects without AD were studied for homocysteine, B vitamin status (folate, vitamin B(12), pyridoxal-5'-phosphate [PLP]), kidney function (creatinine), and thyroid function (thyroid-stimulating hormone, thyroxin). In addition, the presence of vascular disease was assessed by reviewing both medical histories and brain imaging data provided by CT and MRI. RESULTS: The OR for elevated plasma homocysteine (>12 micromol/L) was only 2.2 (not significant) for subjects with AD. In contrast, the OR was 10.0 (p = 0.03) for subjects with vascular disease (n = 26). The OR for low plasma PLP (<25 nmol/L) was 12.3 (p = 0.01) for patients with AD. No significant relationship was observed between vascular disease and PLP level or between plasma homocysteine and PLP concentrations. CONCLUSIONS: Elevated plasma homocysteine in patients with AD appears related to vascular disease and not AD pathology. In addition, low vitamin B(6) status is prevalent in patients with AD. It remains to be determined if elevated plasma homocysteine or low vitamin B(6) status directly influences AD pathogenesis or progression.

Executive dysfunction in subcortical ischaemic vascular disease.

BACKGROUND: Executive dysfunction has been reported in patients with subcortical-frontal pathology, even in the absence of dementia. OBJECTIVE: This study was undertaken to determine if impairments in executive functioning could be found in non-demented patients with subcortical lacunes. METHODS: Cross sectional comparison between older control subjects (n=27) and non-demented patients with one or more subcortical lacunes (n=12). All participants were administered a neuropsychological test battery incorporating three measures of executive functioning, the Stroop interference test, California card sorting test, and the initiation-perseveration subtest of the Mattis dementia rating scale. RESULTS: No group differences were found on measures of recent verbal memory, language, or spatial ability. Normal controls performed better than patients with lacunes in visual memory. On the Stroop interference test, patients with lacunes performed as well as controls on the colour naming condition but slower on the interference condition. Patients with lacunes also generated fewer correct sorts on the California card sort test and achieved lower scores on the initiation-perseveration subtest. Executive measures were correlated with extent of white matter signal hyperintensity but not number of lacunes. CONCLUSION: Subcortical ischaemic vascular disease is associated with subtle declines in executive functioning and visual memory, even in non-demented patients. The pattern of cognitive impairment after subcortical lacunes is consistent with models of subcortical-frontal circuits.

The effects of age on rate of progression of Alzheimer disease and dementia with associated cerebrovascular disease.

BACKGROUND: Relatively little is known about how cerebrovascular disease affects progression of dementia. Previous studies have found no differences in progression of Alzheimer disease and vascular dementia, but these studies have not specifically examined age effects. OBJECTIVE: To test whether the rate of cognitive decline is different in Alzheimer disease compared with dementia with associated cerebrovascular disease in clinical and autopsy patient series. PATIENTS AND METHODS: We studied the longitudinal course of cognitive function as measured by the Mini-Mental State Examination (MMSE) in patients with clinically and neuropathologically diagnosed conditions evaluated through a university Alzheimer disease center. Clinical patients were grouped according to possible Alzheimer disease without stroke (n = 37), probable Alzheimer disease without stroke (n = 181), and dementia with stroke (n = 50). Autopsy cases were categorized into Alzheimer disease (n = 78) and dementia with vascular disease (n = 13). Data were analyzed using random-effects modeling of longitudinal change. RESULTS: There was a significant interaction between age and diagnosis in determining rate of change on the MMSE scores for both the clinical and autopsy samples. Rate of change decreased slightly with advancing age for Alzheimer disease groups, but increased with age for dementia with cerebrovascular disease groups. CONCLUSIONS: Dementia with cerebrovascular disease declined faster in patients 80 years and older compared with Alzheimer disease without associated cerebrovascular pathological conditions, but showed slower decline in patients younger than 80 years. This effect most likely reflects combined Alzheimer and vascular pathological conditions in older patients with cerebrovascular disease.

A new verbal learning and memory test for English- and Spanish-speaking older people.

Word-list verbal learning and memory tests with appropriate normative data can be highly sensitive to cognitive decline, but there are significant limitations of such tests available for use with older Hispanic and non-Hispanic people living in the US. The purpose of this study was to (1) create a new word-list learning and memory test in both English and Spanish and, (2) validate it with respect to sensitivity to cognitive impairment, and (3) develop statistical corrections for the effects of significant demographic variables, including ethnicity, language of administration, age, education, and gender. A community dwelling sample of 801 English- and Spanish-speaking older people was employed. Recall on learning trials and the delayed recall trial of the word-list learning test were strongly related to the Mini-Mental State Examination (MMSE). moderately related to age, and weakly related to gender and education. The relationship of word-list variables and the MMSE did not significantly differ across ethnicity/language groups. Regression coefficients for demographic variables were used in a statistical correction formula to adjust raw word-list scores, and then to develop specific percentile cut-off values.

Frontal lobe hypometabolism predicts cognitive decline in patients with lacunar infarcts.

BACKGROUND: A proportion of patients with subcortical lacunes will suffer progressive cognitive dysfunction, but the basis for this decline is controversial and little is known about predicting cognitive decline in these patients. Studies of Alzheimer disease have shown that imaging measures of temporal and parietal metabolism and blood flow predict disease course. OBJECTIVE: To determine whether regional cerebral glucose metabolism predicts cognitive decline by testing 2 opposing hypotheses: (1) temporoparietal activity predicts decline (based on the idea that concomitant Alzheimer disease causes decline) vs (2) frontal hypometabolism predicts decline (based on evidence that subcortical frontal circuits are especially vulnerable to small vessel ischemia). DESIGN: Prospective cohort study. SETTING: University outpatient dementia center. PATIENTS: A convenience sample of 26 patients with radiologically defined lacunes and baseline cognitive function ranging from normal to moderately demented. MAIN OUTCOME MEASURES: Regional cerebral metabolism was quantitated in the form of atrophy-corrected positron emission tomographic activity ratios in cortical regions that were defined a priori. Patients were followed up at a mean of 1.8 years, and the dependent variable was rate of change in the Mini-Mental State Examination score. RESULTS: Bilateral and right hemisphere dorsolateral frontal metabolism significantly predicted cognitive decline, with right dorsolateral frontal metabolism explaining 19% of the variance. No other positron emission tomographic region was a significant predictor, nor were demographic variables or baseline Mini-Mental State Examination scores significant predictors. CONCLUSION: Cognitive decline in patients with lacunes may result in part from progressive vascular compromise in subcortical frontal circuits.

Context processing in older adults: evidence for a theory relating cognitive control to neurobiology in healthy aging.

A theory of cognitive aging is presented in which healthy older adults are hypothesized to suffer from disturbances in the processing of context that impair cognitive control function across multiple domains, including attention, inhibition, and working memory. These cognitive disturbances are postulated to be directly related to age-related decline in the function of the dopamine (DA) system in the prefrontal cortex (PFC). A connectionist computational model is described that implements specific mechanisms for the role of DA and PFC in context processing. The behavioral predictions of the model were tested in a large sample of older (N = 81) and young (N = 175) adults performing variants of a simple cognitive control task that placed differential demands on context processing. Older adults exhibited both performance decrements and, counterintuitively, performance improvements that are in close agreement with model predictions.

MRI predictors of cognition in subcortical ischemic vascular disease and Alzheimer's disease.

BACKGROUND: Causes of cognitive impairment in subcortical ischemic vascular disease (SIVD) are less well understood than in AD, but have been thought to result from direct effects of subcortical lacunes and white matter lesions, perhaps related to disruption of important cortical-subcortical pathways. OBJECTIVE: To examine the relation between cognitive abilities and quantitative MRI measures of subcortical cerebrovascular disease and cortical and hippocampal atrophy. METHODS: Subjects were 157 participants in a multicenter study of SIVD and AD who included cognitively normal, cognitively impaired, and demented individuals with and without subcortical lacunar infarcts. Dependent variables were neuropsychological tests of global cognitive function, memory, language, and executive function. Independent variables were quantitative MRI measures of volume of lacunar infarcts in specific subcortical structures, volume of white matter lesion (WML), volume of cortical gray matter (cGM), and total hippocampal volume (HV). Multiple regression analyses were used to identify MRI predictors of cognition. RESULTS: Subcortical lacunes were not related to cognitive measures independent of effects of other MRI variables. WML was independently related to selected, timed measures. HV and cGM were strong and independent predictors of cognitive variables, with effects that did not differ in subjects with and without subcortical lacunes. CONCLUSIONS: Results suggest that cognitive impairment associated with subcortical ischemic vascular disease is primarily a result of associated hippocampal and cortical changes.

Hippocampal and cortical atrophy predict dementia in subcortical ischemic vascular disease.

BACKGROUND: The cause of dementia in subcortical ischemic vascular disease (SIVD) is controversial. OBJECTIVES: To determine whether cognitive impairment in SIVD 1) correlates with measures of ischemic brain injury or brain atrophy, and/or 2) is due to concomitant AD. METHODS: Volumetric MRI of the brain was performed in 1) elderly subjects with lacunes (L) and a spectrum of cognitive impairment-normal cognition (NC+L, n = 32), mild cognitive impairment (CI+L, n = 26), and dementia (D+L, n = 29); 2) a comparison group with probable AD (n = 28); and 3) a control group with normal cognition and no lacunes (NC). The authors examined the relationship between the severity of cognitive impairment and 1) volume, number, and location of lacunes; 2) volume of white matter signal hyperintensities (WMSH); and 3) measures of brain atrophy (i. e., hippocampal, cortical gray matter, and CSF volumes). RESULTS: Among the three lacune groups, severity of cognitive impairment correlated with atrophy of the hippocampus and cortical gray matter, but not with any lacune measure. Although hippocampal atrophy was the best predictor of severity of cognitive impairment, there was evidence for a second, partially independent, atrophic process associated with ventricular dilation, cortical gray matter atrophy, and increase in WMSH. Eight autopsied SIVD cases showed variable severity of ischemic and neurofibrillary degeneration in the hippocampus, but no significant AD pathology in neocortex. The probable AD group gave evidence of only one atrophic process, reflected in the severity of hippocampal atrophy. Comparison of regional neocortical gray matter volumes showed sparing of the primary motor and visual cortices in the probable AD group, but relatively uniform atrophy in the D+L group. CONCLUSIONS: Dementia in SIVD, as in AD, correlates best with hippocampal and cortical atrophy, rather than any measure of lacunes. In SIVD, unlike AD, there is evidence for partial independence between these two atrophic processes. Hippocampal atrophy may result from a mixture of ischemic and degenerative pathologies. The cause of diffuse cortical atrophy is not known, but may be partially indexed by the severity of WMSH.

Effect of estrogen on cerebral glucose metabolism in postmenopausal women.

PET was used to evaluate the effect of estrogen use on regional cerebral glucose metabolism in postmenopausal women. Women receiving estrogen replacement therapy (ERT+), women not receiving estrogen (ERT-), and women with AD were studied. The ERT- group showed metabolic ratios that were intermediate to the ERT+ and AD groups, although they did not show any signs of cognitive impairment. These findings show an effect of estrogen depletion on brain metabolic activity.

Memory failure has different mechanisms in subcortical stroke and Alzheimer's disease.

Patients with extensive subcortical cerebrovascular disease may have impaired memory, often despite the absence of medial temporal or diencephalic strokes. In this group, episodic memory failure may arise from frontal lobe dysfunction based on disruption of frontosubcortical loops caused by lacunae. We tested this idea by studying cognitively impaired subcortical stroke (CIS) patients and Alzheimer's disease (AD) patients with [18F]-fluorodeoxyglucose positron emission tomography using a continuous verbal memory task during the period of tracer uptake. Patients were matched on severity of cognitive impairment and overall memory task performance. As hypothesized, we found a double dissociation in the relations between metabolism and memory in these groups, such that memory in CIS (but not in AD) correlates with prefrontal lobe metabolism, whereas in AD (but not in CIS), memory correlates with left hippocampal and temporal lobe metabolism. Analysis of memory subscores showed that CIS patients made more errors on short-delay trials, which is consistent with working memory failure. It seems that different pathogenic mechanisms underlie episodic memory failure in subcortical cerebrovascular disease and AD.