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(Stroke. 2000;31:2182.)
© 2000 American Heart Association, Inc.
Original Contributions |
From the Divisions of Clinical Neurosciences (N.H., H. Kazui, M.H., E.M.) and Neuroimaging Research (H. Kitagaki), Hyogo Institute for Aging Brain and Cognitive Disorders, Himeji, Japan.
Correspondence to Dr Nobutsugu Hirono, Division of Clinical Neuroscience, Hyogo Institute for Aging Brain and Cognitive Disorders, 520 Saisho-ko, Himeji 670-0981, Japan. E-mail hirono{at}hiabcd.go.jp
| Abstract |
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MethodsThe subjects were 76 AD patients who had WMHs but no obvious cerebrovascular diseases. We quantified the volume of WMHs by using fast-fluidattenuated inversion recovery images and whole brain atrophy by using 3D spoiled gradient-echo images. Effects of WMHs and brain atrophy on dementia severity, cognitive function, neuropsychiatric disturbances, and neurological findings were examined.
ResultsWhole brain atrophy was significantly associated with dementia severity and cognitive disturbances, as well as with grasp reflex and some kinds of neuropsychiatric disturbances. After we controlled for the effects of brain atrophy, duration of symptoms, and demographic factors, we found that WMH volume was not associated with global cognitive disturbances or dementia severity but was significantly associated with urinary incontinence, grasp reflex, and aberrant motor behaviors. Brain atrophy and WMH volume were not significantly correlated either before or after controlling for age, sex, education, and duration of symptoms. WMH volume was associated with hypertension, but brain atrophy was not positively correlated with any vascular risk factors.
ConclusionsOur results support the hypothesis that WMHs in AD patients are superimposed phenomena of vascular origin. WMHs contribute to specific neurological and neuropsychiatric manifestations but not to global cognitive impairment, which is more closely associated with brain atrophy.
Key Words: Alzheimer disease atrophy neurological deficits risk factors white matter
| Introduction |
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Some studies have shown a significant relationship between WM changes and certain cognitive functions and/or dementia severity,11 12 13 14 15 16 17 whereas others4 10 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 have failed to find any such relationships in patients with AD. Different study populations and the heterogeneity of WM changes may explain the inconsistency among these studies. Selection of AD patients without vascular risk factors and/or neurological signs may result in excluding severe WM changes and ignoring the clinical significance of WM changes. Small subcortical infarcts frequently accompanied by WM changes,1 2 which do not necessarily exclude the diagnosis of AD by the clinical diagnostic criteria, obscure the independent effects of WM changes by affecting the strategic sites causing dementia.24 In some studies, periventricular changes in the form of caps or smooth halos were included, with irregular confluent changes in the deep and periventricular WM. The former changes are apparently of nonischemic origin, whereas the latter changes represent ischemic tissue damage.33 34
In addition, the neuroimaging technique used is an important factor. MRI is more sensitive to WM changes than is CT.35 36 37 38 Although WM changes have been semiquantified with a visual rating scale in most studies, none of these scales have been validated, and the concordance of different scales is insufficient.39 Although MRI quantification of WM changes is desirable, a manual outlining of WM changes12 25 is essentially dependent on visual inspection that may be affected by an arbitrary gray scale used for display and filming. Computer-based thresholding methods for voxel intensities40 41 are preferable. Finally, the effect of brain atrophy has rarely been considered,16 29 although some studies4 13 22 have analyzed the cerebrospinal fluid space. Because diffuse brain atrophy, which is a main gross pathological feature of AD, is an index of neuronal and synaptic loss, brain atrophy should also be taken into consideration in analyzing the impact of WM changes on cognitive function.
In the present study, we examined a purely selected cohort of patients with AD who had WM changes but no obvious cerebrovascular diseases so as to determine the effect of WM changes on cognitive, neurological, and neuropsychiatric symptoms. We quantified the volume of WM hyperintensities (WMHs) and brain atrophy on MRI by means of computer-based techniques. We also tested the hypothesis that WM changes are associated with vascular risk factors but not with brain atrophy.
| Subjects and Methods |
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Subjects
All procedures of the present study strictly followed the
1993 Clinical Study Guidelines of the Ethics Committee of HI-ABCD and
were approved by the Internal Review Board. After a complete
description of all procedures of the present study, written
informed consent was obtained from patients or their
relatives.
On the basis of the following inclusion/exclusion criteria, 76 AD patients were selected from a consecutive series of 391 patients with dementia who were given a short-term admission for examination to the HI-ABCD infirmary between April 1997 and March 1999. All patients were examined by both neurologists and psychiatrists with standardized medical history inquiries, neurological examinations, routine laboratory tests, electroencephalography, magnetic resonance (MR) images of the brain, and MR angiography of the head and neck. The inclusion criteria were those identified by (1) the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, revised for dementia42 ; (2) the presence of WM changes, which were defined as irregular periventricular, early confluent deep, or confluent deep WMHs on T2-weighted MRI according to Fazekas and colleagues34 43 and our previous report44 ; and (3) the National Institute of Neurological and Communicative Disorders and Stroke, Alzheimers Disease and Related Disorders Association, for AD45 when disregarding WM changes.
Although 234 patients fulfilled the inclusion criteria, 158 patients were excluded from the present study in accordance with the exclusion criteria. Excluded were patients (1) with medical illnesses possibly causing cognitive impairment or WM lesions, including demyelinating diseases, thyroid diseases, vitamin deficiencies, and malignant diseases with or without antineoplastic agents (n=23); (2) with focal brain lesions, including lacunar infarcts and hematoma (n=84); (3) with complication of developmental abnormalities, mental diseases, substance abuse, or significant neurological antecedents, such as brain trauma, brain tumor, epilepsy, and inflammatory disease (n=21); (4) with evidence of severe intracranial or cervical arterial occlusive lesions on MR angiography (n=1); and (5) whose informed consent was not obtained (n=29).
The subjects consisted of 64 women and 12 men; the mean±SD age at examination was 75.6±7.1 years, and the mean educational attainment was 8.8±2.0 years. The mean duration of symptoms, determined through an interview with the primary caregiver and defined as the time between the first appearance of symptoms of sufficient severity to interfere with social or occupational functioning and the admission,46 was 30.8±19.4 months. The functional severity was very mild in 7 patients, mild in 41 patients, moderate in 22 patients, and severe in 6 patients, as determined by the Clinical Dementia Rating Scale (CDR).47 No patient had a history of stroke.
Assessment of Vascular Risk Factors and Neurological
Disturbances
Hypertension, diabetes mellitus, lipid disorder, smoking habit,
drinking habit, and cardiac diseases were evaluated as vascular risk
factors. Hypertension was judged as present when either a
systolic pressure of >160 mm Hg or a
diastolic pressure of >95 mm Hg was demonstrated on
repeated examinations or when a history of treatment for hypertension
was present. Diagnosis of diabetes mellitus was made when the
fasting blood glucose level was >7.770 mmol/L (140 mg/dL) or when
a history of treatment for diabetes mellitus was present. Lipid
disorder was judged as present when laboratory examination of the
serum at presentation showed a total
cholesterol level of >5.698 mmol/L (220 mg/dL), a
triglyceride level of >1.695 mmol/L (150 mg/dL), or
an HDL cholesterol level of <1.036 mmol/L (40 mg/dL)
or when a history of treatment was present. Smoking habit was
defined as
1 cigarette/d for
1 year, and drinking habit was defined
as
30 mL ethanol equivalent per day for
1 year sometime in life.
Cardiac diseases were assumed to be present whenever there was a
known history or clinical demonstration of any kind of heart disease,
including myocardial infarction, angina pectoris, and
arrhythmia.
A careful neurological examination was given to document the presence or absence of hemiparesis, sensory loss, visual field defects, postural instability (gait disturbance and/or pulsion), pyramidal signs (hyperreflexia, spasticity, and/or extensor plantar responses), extrapyramidal signs (resting tremor, bradykinesia, and/or rigidity), pseudobulbar palsy, ataxia, grasp reflexes, and urinary incontinence. No attempt was made to grade the severity of these risk factors or neurological abnormalities.
Assessment of Cognitive Function and Neuropsychiatric
Status
We assessed the cognitive function of the patients with the
Mini-Mental State Examination,48 Wechsler Adult
Intelligence ScaleRevised,49 and Alzheimers
Disease Assessment ScaleCognitive Part.50 The 10-word
list recall subtest of the Alzheimers Disease Assessment
Scale was also analyzed separately. The patients behavioral
changes were assessed semiquantitatively during an interview with the
caregiver by using the Neuropsychiatric Inventory (NPI).51
In the NPI, the following 10 behavioral changes in dementia were rated
on the basis of the condition of the patients in the previous month
before the interview: delusions, hallucinations, depression
(dysphoria), anxiety, agitation and aggression, disinhibition,
euphoria, irritability and lability, apathy, and aberrant motor
activity. According to the criterion-based rating scheme, the severity
of each manifestation was classified into 4 grades (from 0 to 3), and
the frequency of each manifestation was classified into 5 grades (from
0 to 4). The NPI score (severityxfrequency) was calculated for each
manifestation (range of possible scores 0 to 12). All clinical measures
were taken with the investigators blinded to the inclusion of subjects
in the present study.
MR Acquisition
MR was performed on a 1.5-T superconducting magnet (Signa
Advantage, General Electric Medical Systems). Axial double-echo
fast-spin echo T2-weighted images (3000/105/2 [repetition
time/effective echo time/excitations]), spin-echo T1-weighted images
(550/15/2), and fast-fluidattenuated inversion recovery (FLAIR)
images (9002/147/2200/1 [repetition time/effective echo time/inversion
time/excitations]) were obtained for 14 locations parallel to the
anteroposterior commissure plane with a section thickness of 5 mm
and intersection gap of 2.5 mm covering the area from the base of
the cerebellum to the vertex. In all acquisitions, the field of view
was 200x200 mm, and the matrix size was 256x256. All scans were
reviewed by one neuroradiologist without knowledge of the patients
clinical data. Lacunar infarcts were specified as lesions with
diameters of
15 mm with (1) hyperintensity on T2-weighted
images, (2) distinct hypointensity on T1-weighted images, and (3)
hyperintensity with central hypointensity on FLAIR images. By use of
these criteria, lacunar infarcts can be distinguished from the
état cribré or punctuate hyperintensity form of
WMHs.52 For measurements of whole brain volume (WBV) and
total intracranial volume (TIV), we also obtained coronal, 3D, spoiled
gradient-echo images (11.1/2/2 [repetition time/effective echo
time/excitations]). The field of view was 220x220 mm, the matrix
size was 256x256, contiguous sections were 124x1.5 mm, and the
flip angle was 20°. The images were generated perpendicular to the
anteroposterior commissural plane, which covers the whole
calvarium.
Measurement of Volume of WMHs
We used FLAIR images for quantification of WMH volume. FLAIR is
a heavily T2-weighted inversion-recovery technique that nulls fluid,
such as cerebroventricular fluid. By use of this technique,
subtle periventricular WM lesions can be easily recognized,
and their extents can be assessed on a background of cerebrospinal
fluid and normal WM. This technique has been reported to be useful for
examining WM diseases, such as multiple sclerosis, cerebral infarction,
and leukoaraiosis.53 54 The MR data sets of all images
were directly transmitted to a personal computer (Power Macintosh
8100/80, Apple) from the MR unit and analyzed by means of the
public-domain National Institutes of Health Image version 1.61 program
(written by Wayne Rasband and available from the Internet by anonymous
ftp from zippy.nimh.nih.gov or on floppy disk from NTIS, 5285 Port
Royal Rd, Springfield, VA 22161, part No. PB93-504868) with residential
macro programs developed in our institution. To fit a limitation of the
software (8-bit voxel value), 12 bits of MR voxel data were converted
to 8 bits at a scale factor of 0.5 by the minimum (voxel value 0) and
maximum (voxel value 510) levels. Basically, we used a semiautomatic
segmentation technique through intensity thresholding, thereby avoiding
the observers bias. The segmentation thresholding for WMHs was a
priori determined to be 3.5 SDs in voxel intensity levels of the normal
WM. The outline of WMHs with the surrounding normal WM, gray matter,
and cerebroventricular fluid was first traced with a
manually driven mouse cursor (Figure
).
The volume of WMHs was obtained by automatically counting the number of
voxels that showed signal intensities higher than the threshold within
this outline and then by multiplying the number by the voxel size
[(200/256)2x7.5= 4.58
mm3]. Because some normal gray matter
demonstrated signal intensities higher than the threshold, we carefully
excluded these highsignal-intensity gray matter structures as far as
possible. Measurements were performed by another investigator blinded
to the clinical information. The test-retest reliability for this
method was examined with 20 patients, and a high intraclass correlation
coefficient was obtained (r=0.969).
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Measurement of WBV and TIV
The detailed MRI procedure for obtaining WBV and TIV is
described elsewhere.55 In brief, the data sets of all
spoiled gradient-echo images were directly transmitted to a graphic
workstation (INDIGO II HighImpact, Silicon Graphics) from the MRI unit
and were analyzed with 3D MRI-analyzing software developed by
Yamato et al.56 The software makes use of a combination of
a gray-scale algorithm (a 3D expansion of the region-growing method),
an edge-detection algorithm (a 3D expansion of Sobel filtering),
and some a priori knowledge. With this software, the whole brain
was segmented by detecting the boundary between the cerebrospinal fluid
and gray matter, and the calvarium was extracted by detecting the outer
surface of the dura mater. WBV and TIV were calculated by multiplying
the number of voxels in the extracted regions by the voxel size. The
caudal end of the whole brain and calvarium was manually set at the
plane intersecting the occipitoatloid junction, which is the only
supervised operation required. The appropriateness of the extraction of
the whole brain and calvarium was assessed by 2 reviewers who were
blinded to the clinical data and who examined on-site 3D reconstruction
displays of elective view points and 2D slice images of selected
sections. The reliability and validity of this method have been
established and are described elsewhere.55 57 The
measurements were performed by the same neuroradiologist who reviewed
the MR images. To adjust for premorbid brain volume variability, WBV
was normalized by dividing it by TIV. A smaller normalized WBV (nWBV)
indicates a greater brain atrophy.
Statistical Analysis
We used nonparametric statistics because many
variables were not normally distributed. Computation was performed
with the SAS program package, release 6.12 (Statistical
Analysis Systems). The relationship between vascular risk
factors and WMH volume was examined by using partial Spearman rank
correlation coefficients, where the effects of age, sex, education,
duration of symptoms, and brain atrophy (nWBV) were controlled.
Similarly, the relationship between vascular risk factors and brain
atrophy (nWBV) were examined while controlling the effects of the
confounding variables and WMH volume. The effects of WMH volume and
nWBV on neurological signs, cognitive functions, CDR, and the NPI
scores were also tested by using partial Spearman rank correlation
coefficients; age, sex, duration of symptoms, and education level were
entered into the models. The effect of nWBV or WMH volume was also
controlled in each analysis. For all analyses, the
statistical
level was set at 0.05.
| Results |
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There was a highly significant negative correlation between age
and nWBV even after controlling for the effects of the confounding
variables and volume of WMHs (Table 2
). Although the relationship between
volume of WMHs and age was significant in a univariate
analysis, it did not remain significant after controlling for
the effect of the confounding variables and nWBV. Similarly, the
relationship between nWBV and the duration of symptoms was significant
only before controlling for the effects of the confounding
variables and volume of WMHs. Table 3
describes partial Spearman rank correlation coefficients between the
volume of WMHs and the risk factors and between nWBV and the risk
factors. WMH volume was positively correlated with hypertension. nWBV
was positively correlated with smoking (nWBV was larger in smokers).
Table 4
summarizes the partial Spearman
rank correlation coefficients of volume of WMHs and nWBV with
neurological disturbances, CDR, cognitive test scores, and NPI
scores after controlling for the effects of the confounding
variables. The volume of WMHs was significantly correlated with
incontinence and grasp reflex and with the NPI aberrant motor behavior
scores but not with cognitive test scores or CDR. On the other hand,
nWBV was significantly correlated with all cognitive test scores and
CDR, with grasp reflex, and with NPI disinhibition and aberrant motor
behavior scores.
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| Discussion |
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In the present study, WMH volume was not correlated with the severity of dementia, global cognitive impairment, or memory impairment. This finding is compatible with the findings of our previous study,61 in which we demonstrated that WMHs were associated with decreased cerebral blood flow but not with decreased oxygen metabolism in patients with AD. Brain atrophy, but not reduced cerebral blood flow, was significantly associated with cognitive impairments. These findings suggest that the cognitive impairment in our patients is not attributable to WM changes but to brain atrophy, although WM changes are reported to impair some cognitive functions that were not evaluated in the present study.11 WMHs associated with more severe small-vessel diseases might affect cognitive functions in patients with AD. Snowdon et al62 reported that in subjects with pathological evidence of AD, those lacunar infarcts in the basal ganglia, thalamus, or deep white matter had poorer cognitive function and a higher prevalence of dementia than those without infarcts. However, even in patients who were diagnosed as having vascular dementia, the association between WM changes and global cognitive impairment is unconvincing.10 11 22 25 63 64 65 66 Although Binswangers disease reportedly causes dementia without a cortical degenerative process, the pathological features of this disorder include not only WM changes but also lacunar infarcts in the basal ganglia and thalamus.1 2 Coexistent lacunar infarcts may affect the strategic sites, causing dementia.67 Inzitari et al68 pointed out that a strong association between WM changes and dementia was an epiphenomenon that could be explained by a history of stroke. In a longitudinal study of patients with lacunar infarcts, Loeb et al69 found that the development of dementia was significantly associated with cerebral atrophy and new focal cerebrovascular episodes but not with WM changes. These findings, together with those in the present study, suggest that cognitive impairment, both in AD and vascular dementia, is not principally attributable to WM changes.
On the other hand, the present study clearly demonstrated that WM changes and brain atrophy were independently associated with certain neurological and neurobehavioral signs. Urinary incontinence, grasp reflexes, and aberrant motor behaviors were significantly correlated with WMH volume even after controlling for brain atrophy, although the latter 2 were also correlated with brain atrophy after controlling for WMH volume. Urinary incontinence is considered to be one of the central clinical features of Binswangers disease,1 2 and an involvement of WM changes in its development has been shown in previous studies.23 24 Primitive reflexes have also been reported to be associated with WM changes in elderly people70 71 and in patients with dementia.72 Positive associations between WM changes and psychiatric symptoms have been reported in subjects without dementia.73 74 Although previous studies have failed to find a relationship between WM changes and neurobehavioral signs in patients with dementia,14 21 28 30 the present study clearly demonstrated that WM changes were involved in the development of aberrant motor behaviors. Aberrant motor behaviors, including wandering, pacing, and rummaging, belong to repetitive and excessive behaviors, which are likely to be caused by frontal lobe dysfunction. Our findings indicate that WM changes would at least add frontal loberelated neurological and neurobehavioral features as manifestations of dementia.
In conclusion, WM changes in AD patients without any obvious cerebrovascular diseases are related to hypertensive microangiopathy and are independent of brain atrophy that would be attributable to a degenerative process. WM changes contribute to the development of some frontal loberelated neurological and neurobehavioral signs but not to the development of a global cognitive impairment, which is more closely associated with brain atrophy. Further studies are needed to generalize our findings to include AD patients with more severe vascular disease.
| Acknowledgments |
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Received May 5, 2000; revision received June 16, 2000; accepted June 16, 2000.
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