Cognition and white matter changes on magnetic resonance imaging in dementia

Diagnosis of vascular dementia: Consortium of Canadian Centres for Clinical Cognitive Research concensus statement

Interest in vascular causes for cognitive impairment is increasing, in recognition that such causes are common, and possibly preventable. This has led to attempts to better define vascular dementia and its natural history. Several sets of criteria for the diagnosis of vascular dementia have been proposed. We provide a brief overview of the background to the initiation of a Canadian consensus conference, established by the Consortium of Canadian Centres for Clinical Cognitive Research (C5R) and report the conclusions reached at that conference. To date, no one set of criteria is demonstrably superior to another; we have therefore not endorsed any of the competing sets, nor have we recommended our own. Instead we suggest that empiric studies are required to establish valid criteria. A diagnostic checklist, which combines existing criteria and additional data, is attached for clinicians wishing to participate in such studies.

Improvements to the quality of MRI cluster analysis

Cluster analysis techniques are gaining widespread use for segmentation of MRI data, especially for volume measurement and 3-D display purposes. This paper describes four improvements to such techniques: (1) The use of intensity simulations to model cluster plots; (2) Correction of image nonuniformity; (3) Anisotropic smoothing of data; and (4) Automatic isolation of tissues of interest. Simulation of cluster plots allows an informed choice of pulse sequence(s) and acquisition parameters to be made. Correction of image nonuniformity and anisotropic smoothing reduce the spread of signal intensity from a single tissue thus producing significantly more compact clusters, whilst the isolation of tissues of interest prevents overlap of clusters from the tissues of interest with those not under consideration. These techniques may be used to improve the results of cluster analysis or traded off, for example to allow lower signal-to-noise images, shorter repetition time images, or fewer images to be used for segmentation.

Relation between MRI features and dementia in cerebrovascular disease patients with leukoaraiosis: a longitudinal study

We examined selective MRI features (localization and degree of white matter abnormalities, cortical and subcortical atrophy) in relation to cognitive decline in patients with cerebrovascular disease (CVD) and leukoaraiosis (LA). We enrolled 6 female and 18 male CVD patients (mean age 66.2 +/- 6.6 years) whose Magnetic Resonance Images (MRI) revealed LA and who displayed a history of stroke or TIA; none showed signs of cortical infarcts or normal pressure hydrocephalus. Two blind raters independently scored MRI scans with a high level of agreement. All patients underwent extensive clinico-neuropsychological assessment upon admission to the study and 19 were followed for an average of 48 +/- 7.6 months. Twelve patients were initially classified as non-demented and 12 as demented. Three years later, one in the former group had become demented and mental impairment had worsened for 6 patients in the latter group; these 7 subjects were labeled as "decliners". Ventricular indexes were significantly higher in the demented group and correlated with severity of mental impairment, while the degree of LA was similar in demented and non-demented subjects. Neither white matter lesions nor sulcal and ventricular enlargement differed statistically between decliners and non-decliners.

Patterns of neuropsychological performance in Alzheimer's disease and vascular dementia

The hypothesis that Alzheimer's disease (AD) and vascular dementia (VD) may be associated with specific patterns of neuropsychological dysfunction was tested by assessing sensory-motor performance, attention, memory, visuospatial functions, verbal ability, and intelligence in AD (N = 83) and VD (N = 42) patients stratified into four levels of severity based on the Mini-Mental State Examination. Results showed a progressive deterioration due to severity of dementia in both AD and VD patients in all cognitive tasks, but not in the sensory-motor tasks, and no significant interaction between type and severity of dementia in any measure, indicating a similar pattern and course of neuropsychological deterioration in AD and VD. Yet it was possible to differentiate the two groups with moderate success using tests drawing predominantly on motor speed and, to a lesser extent, on cognitive speed. In all these speeded tests, the AD patients outperformed the VD patients.

Correlations of leuko-araiosis with cerebral atrophy and perfusion in elderly normal subjects and demented patients

CT images of leuko-araiosis in brain slices were quantified according to volumes of reduced Hounsfield units in frontal periventricular white matter in groups of elderly patients with multi-infarct dementia (MID, n = 23) and dementia of the Alzheimer type (DAT, n = 16). Volumes of leuko-araiosis, estimates of atrophic cerebral tissue, and local cerebral perfusion utilising inhalation of xenon gas as the indicator were correlated on the same CT slices. Ratios of frontal leuko-araiosis to total brain tissue volume were similar for patients with MID and DAT (mean 5.7 (SD 2.1)% v 6.5 (3.2%)), and both were significantly greater than ratios in elderly normal volunteers (3.1(1.3)%, 0 < 0.001). Cerebral atrophy (measured as the ratio of volumes of cerebrospinal fluid to total brain area) for DAT patients was 17.0 (6.7)%, which was greater than for MID patients (12.5 (5.4)%; p < 0.05) and both types of patients showed more cerebral atrophy than did age matched, elderly normal subjects. Cerebral perfusion was decreased in all regions measured in patients with MID and DAT compared with elderly normal subjects. Multi variate regression analyses correlated frontal leuko-araiosis with reductions of local cerebral blood flow in subcortical grey matter (p < 0.025) in patients with vascular dementia but not in those with DAT. These quantitative measures implicate decreased perfusion due to atherosclerosis in territories supplied by the deep penetrating cerebral arteries in the pathogenesis of leuko-araiosis in patients with vascular dementia, but suggest a different pathogenesis for leuko-araiosis in Alzheimer's disease.

Proton magnetic resonance spectroscopy with dementia

To provide new insights into metabolic changes in the brain of patients with dementia, we performed in vivo localized proton magnetic resonance spectroscopy in nine patients with primary degenerative dementia and in three patients with normal-pressure hydrocephalus. We compared the results with those in 26 healthy volunteers. Measurements of regional cerebral blood flow were performed in seven patients by means of single photon emission computed tomography with amphetamine I 123 as a tracer. The magnetic resonance spectra constantly showed three major peaks corresponding to N-acetylaspartate (NAA), creatine and phosphocreatine (Cr), and choline-containing compounds. There were no age-related changes in the mean area ratio of NAA to Cr in neurologically normal volunteers. The NAA/Cr ratio was significantly reduced in patients with primary degenerative dementia. The reduction of the NAA/Cr ratio was observed even in dementia patients with no significant brain atrophy or reduction in regional cerebral blood flow. No significant reduction of the NAA/Cr ratio was seen in patients with normal-pressure hydrocephalus. The NAA/Cr ratio might reflect the number and/or activity of neuronal cells in the brain. Proton magnetic resonance spectroscopy may well provide a useful tool for early detection of, and further pathophysiological study of, primary degenerative dementia.

Periventricular white matter changes and oropharyngeal swallowing in normal individuals

Cranial magnetic resonance imaging (MRI) has revealed patchy periventricular white matter lesions or "unidentified bright objects" (UBOs) in otherwise neurologically intact individuals. Quantitative videofluoroscopic swallowing evaluations and cranial MRI examinations were studied in 49 neurologically normal volunteers (ages 43 to 79 years). Total swallowing duration (TSD) and its subcomponents of oral transit duration (OTD), stage transition duration (STD), and pharyngeal response duration were measured for liquid and semisolid swallows. MRIs were graded from 0, or no UBOs, to 3, or multiple and confluent lesions. The effect of the presence of UBOs on swallowing durational measures and risk factors was analyzed with age differences accounted for statistically (ANCOVA). TSD and OTD for semisolids were significantly differentiated by MRI score (P less than 0.009 and P less than 0.047, respectively). That is, a demonstrable effect was found for an increased number of UBOs on duration of oropharyngeal swallowing in normal individuals.

Medial temporal atrophy as a magnetic resonance imaging marker for Alzheimer's disease

Medial temporal lobe atrophy (MTLA) on brain magnetic resonance imaging (MRI) may help differentiate Alzheimer's disease (AD) from multiinfarct dementia (MID) and other dementias. MTLA was seen in 6 of 11 patients with clinically diagnosed AD, 16 of 20 with mixed dementia (with both AD and MID), 1 of 5 with psychiatric disease, and in none of 32 with MID or 8 with other dementias (p less than 0.0001). Increased patchy periventricular signal, or "unidentified bright objects" were seen in 2 of 11 patients with AD, 10 of 20 patients with AD and MID, and 26 of 32 patients with MID. A larger series with autopsy correlation may verify that MTLA is a reasonably specific marker for AD, and unidentified bright objects are a sensitive, but not specific, marker for vascular dementias.

Patterns of cerebral hypoperfusion compared among demented and nondemented patients with stroke

BACKGROUND AND PURPOSES

No reports are available that compare local cerebral perfusion among groups of patients suffering from multiple cerebral infarctions with and without cognitive impairments. The present study was designed to correlate changes in regional cerebral perfusion that may lead to dementia among patients with multiple cerebral infarctions by comparing measurements of local cerebral blood flow.

METHODS

Local perfusion was measured using xenon-contrasted computed tomographic scanning among two groups of patients who had suffered from multiple cerebral infarctions: Group D (n = 12) were demented and had severe cognitive impairments, and group I (n = 11) were cognitively intact. Results were compared with similar measurements among neurologically and cognitively normal, age-matched volunteers (group N, n = 16).

RESULTS

Mean local perfusion values were reduced among both groups with cerebral infarctions but to a more marked degree in group D (p less than 0.05). Perfusion of cerebral white matter was diffusely and severely reduced in group D (p less than 0.05) but was mildly reduced only in frontal and capsular white matter in group I (p less than 0.05). Perfusion of cerebral cortex was reduced in frontal (p less than 0.01) and temporal (p less than 0.01) regions among both groups but to a significantly greater degree in group D subjects (frontal, p less than 0.05; temporal, p less than 0.01), who also showed hypoperfusion of the occipital cortex (p less than 0.05), apparently because of underlying leukoaraiosis and cortical disconnections. Perfusion of the basal ganglia was reduced to the same degree among both groups of stroke patients (p less than 0.01).

CONCLUSIONS

Leukoaraiosis with white matter hypoperfusion appears to be an important determinant for cognitive impairments among patients with multiple cerebral infarctions.

Primary or depressive dementia: mental status screening

In the course of interviewing a patient, several aspects of everyday functioning must be covered to provide a range of observations necessary to suggest a provisional diagnosis. First organized by Adolf Meyer, the mental status examination consists of several techniques which, in recent times, have been shortened, structured and standardized to cover maximal ground in minimal time. In this article, the most popular scales are reviewed psychometrically for their capacity to detect, as first-stage instruments, cognitive impairment suggestive of primary dementia in the context of varying prevalence rates and confounding factors like sensory impairments, sociodemographics and depressive states. Several of the measures are found adequate in some respects though not in others, but all of the better ones, when used as front line implements during clinical intake, regularly improve detection over base rates. An analytical method modelled on ROC procedures is then described contrasting two of them before newer instruments are considered which aim to improve sensitivity at relatively little cost to specificity.

Leuko-araiosis and cerebral hypoperfusion compared in elderly normals and Alzheimer's dementia

OBJECTIVE

To elucidate the pathogenesis of leuko-araiosis in patients with Alzheimer's disease by utilizing CT densitometry of the brain and measurements of local perfusion in order to quantify the extent of leuko-araiosis and local hypoperfusion compared with similar measurements made among age-matched normal volunteers.

DESIGN

Cross-sectional case-control study.

SETTING

Out-patient visits to a specialized laboratory located in a large hospital facility.

PATIENTS

Eighteen elderly patients with probable dementia of Alzheimer type (DAT, aged 71.8 +/- 5.1 years) and 17 neurologically and cognitively normal, age-matched volunteers (aged 68.2 +/- 9.6 years) were admitted to the study according to established criteria.

INTERVENTION

None

MAIN OUTCOME MEASURES

Cerebral blood flow (mL/100 g brain/min) estimated by the xenon inhalation CT-CBF method correlated with volume percentage ratio (%) measured by CT densitometry for leuko-araiosis, compared to normal white and gray matter.

RESULTS

Perfusion values for frontal and occipital white matter as well as frontal, parietal, temporal, and occipital cortex were all decreased in DAT patients. Ratios for leuko-araiosis to total brain tissue volumes were greater among patients with DAT compared with age-matched normal volunteers. White matter perfusion in zones of leuko-araiosis was decreased to a similar degree in both DAT and elderly normal volunteers.

CONCLUSIONS

Perfusion is reduced to the same degree in regions of leuko-araiosis in elderly normals as in DAT patients, but the extent of leuko-araiosis is greater among DAT patients and presumably contributes to cognitive impairments.

Quantitative estimation of brain white matter abnormalities in elderly subjects using magnetic resonance imaging

Twenty-five elderly subjects were examined with brain magnetic resonance imaging (MRI). The subjects were divided into two groups: those with Mini-Mental State Examination (MMSE) scores above 25, and those subjects with MMSE scores between 18 and 24. The degree of white matter abnormalities (WMA) (expressed as relative volumes) as well as the presence of cerebrovascular risk factors were evaluated in the two groups. We found that a) subjects with low MMSE scores had significantly larger relative volumes of WMA than the subjects with higher scores, b) a significant correlation (rs = 0.53, p < 0.009) between MMSE scores and the relative volume of WMA was also established, and c) a weak significant correlation (rs = -0.51, p < 0.05) between arterial blood pressure and WMA was found in the subjects with high MMSE scores. Besides these findings no other correlations between the presence of cerebrovascular risk factors and WMA were found in any of the groups.

Leukoaraiosis correlates with cerebral hypoperfusion in vascular dementia

Leukoaraiosis quantified by computerized densitometric measurements of reduced Hounsfield numbers was correlated with local cerebral blood flow on the same computed tomographic images of 35 patients with multi-infarct dementia and 16 age-matched elderly normal volunteers. The ratio for area of frontal leukoaraiosis to total area of parenchyma among the patients was significantly greater than that among the normal volunteers (5.8 +/- 2.3% compared with 3.1 +/- 1.3%, p less than 0.001). Severity of leukoaraiosis around the frontal horns of the lateral ventricles correlated significantly with severity of leukoaraiosis of the centrum semiovale adjacent to the bodies of the lateral ventricles. Cerebral blood flow values for all representative cerebral regions except the parietal white matter were reduced among the patients compared with the normal volunteers. Multivariate regression analysis revealed that reduced cerebral perfusion in the putamen and thalamus correlated significantly with the severity of leukoaraiosis. Cerebral hypoperfusion in territories supplied by deep penetrating arteries may contribute to the pathogenesis of leukoaraiosis.

Magnetic resonance imaging in biological psychiatry

1. Although clinicians have been quick to adopt magnetic resonance imaging (MRI) in the search for brain pathology in psychiatric disorders, the clinical utility of MRI is only now being well defined. 2. Numerous past computerized tomography or post-mortem tissue reports in patients with schizophrenia, affective disorders, dementia, autism, and many other psychiatric illnesses have suggested neuroanatomical substrates for these disorders. However, these techniques have several limitations. 3. The advent of MRI has allowed a high resolution method for examining the brain in vivo. It is important for psychiatrists to know the clinical utility, and the advantages/disadvantages of MR compared with CT. 4. In this article, the authors review the relevant MR literature with some illustrative cases where MRI provided clinically useful information. Recent advances in MRI technology that will have future applications in psychiatry are also discussed.