22ournal ofNeurology, Neurosurgery, and Psychiatry 1994;57:202-207

Cognitive impairment after stroke: frequency,patterns, and relationship to functional abilities

T K Tatemichi, DW Desmond, Y Stem, M Paik, M Sano, E Bagiella

AbstractCognitive function was examined in 227patients three months after admission tohospital for ischaemic stroke, and in 240stroke-free controls, using 17 scoreditems that assessed memory, orientation,verbal skills, visuospatial ability, abstractreasoning, and attentional skills. Afteradjusting for demographic factors withstandardised residual scores in all sub-jects, the fifth percentile was used forcontrols as the criterion for failure oneach item. The mean (SD) number offailed items was 3-4 (3.6) for patientswith stroke and 0-8 (1.3) for controls(p < 0-001). Cognitive impairment,defined as failure on any four or moreitems, occurred in 35-2% of patients withstroke and 3-8% of controls (p < 0-001).Cognitive domains most likely to bedefective in stroke compared with con-trol subjects were memory, orientation,language, and attention. Among patientswith stroke, cognitive impairment wasmost frequently associated with majorcortical syndromes and with infarctionsin the left anterior and posterior cerebralartery territories. Functional impair-ment was greater with cognitive impair-ment, and dependent living afterdischarge either at home or nursinghome was more likely (55.0% with, v32-7% without cognitive impairment,p = 0-001). In a logistic model examiningthe risks related to dependent living afterstroke, cognitive impairment was a sig-nificant independent correlate (oddsratio, OR = 2-4), after adjusting for age(OR = 5'2, 80 + v 60-70 years) and phys-ical impairment (OR = 3.7, Barthelindex < 40 v > 40). It is concluded thatcognitive impairment occurs frequentlyafter stroke, commonly involving mem-ory, orientation, language, and attention.The presence of cognitive impairment inpatients with stroke has important func-tional consequences, independent of theeffects of physical impairment. Studiesof stroke outcome and interventionshould take into account both cognitiveand physical impairments.

(7 Neurol Neurosurg Psychiatry 1994;57:202-207)

Cerebrovascular disease is an important causeof morbidity in the elderly, resulting not onlyin physical disability, but also significant

cognitive impairment. Most studies of strokeoutcome have focused on physical conse-quences;' few have examined intellectualdeficits.2 In a previous study, we founddementia in 66 (26.3%) of 251 elderlypatients examined with neuropsychologicaltests three months after hospital admissionfor ischaemic stroke.3 Excluding subjects withfunctional impairment preceding stroke onsetwho may have had coexisting Alzheimer's dis-ease, the frequency of dementia in this sam-ple was 16-3% (37 of 227 patients withstroke). Our research criteria for dementiarequired the presence of memory impairmentcombined with deficits in two additional cog-nitive domains. Because the frequency ofdementia will depend in part on the diagnos-tic criteria used,4 the frequency of intellectualdecline may be over-represented or under-represented by focusing on dementia as adiagnosis.An alternative approach to characterising

the cognitive consequences of stroke wouldbe to examine a broad range of specific neu-ropsychological deficits, independent of thediagnosis of dementia. If those deficits areclinically meaningful, they should be relatedto functional abilities, whether or not demen-tia is diagnosed. In this report, our aim was todetermine the frequency and patterns of cog-nitive impairment in our cohort of patientswho had no history of functional declinebefore stroke, compared with control subjectswho lived in the community and who werefree of stroke and similar in age. In addition,we related those findings to functional abili-ties and independent living after discharge, todetermine whether our measure of cognitiveimpairment was relevant to adaptive func-tioning. Our overall goal was to providedescriptive information about general intel-lectual functions in a consecutive stroke sam-ple that should have implications for studiesof stroke outcome and intervention.

Subjects and methodsSUBJECT SELECTIONSubjects for this study were recruited amongpatients admitted consecutively to Columbia-Presbyterian Medical Center between 1September 1988 and 31 December 1990 withacute ischaemic stroke occurring within theprevious 30 days. Eligible patients were 60years of age or older, of either sex, with thediagnosis of ischaemic stroke of any type con-firmed by computed tomography of the brain(normal or focal, low density lesion) per-

Columbia University,College ofPhysiciansand Surgeons, NewYork, NY, USADepartnent ofNeurologyT K TatemichiD W DesmondY SternM SanoDepartment ofPsychiatryY StemDivision ofBiostatisticsM PaikE BagiellaGertrude H.Sergievsky CenterY StemCorrespondence to:Dr Tatemichi, Stroke andAging Research Project,Neurological Institute ofNew York, 710 West 168thStreet, New York,NY 10032, USA.Received 23 December 1992and in revised form13 April 1993.Accepted 19 April 1993

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formed within one week of symptom onset.Patients were excluded when certain clinicalfeatures prevented a reliable assessment ofneuropsychological function, such as a severeaphasia-that is, a score of less than three onthe asphasia severity rating scale5 from theBoston diagnostic aphasia examination(BDAE); persistent impairment in conscious-ness from any cause; or primary languageother than English or Spanish. Among the251 patients enrolled and examined threemonths after the onset of stroke, we selected227 patients for this analysis, after excluding24 who were considered to have possible orprobable Alzheimer's disease complicated bystroke, based on a history of functionalimpairment preceding stroke and dementiadocumented by neuropsychological testing.A control group was assembled as a refer-

ence sample, consisting of 249 subjects livingin the community who were over 60 years ofage, and without historical or clinical evi-dence of stroke. Whenever they were avail-able, we recruited as the control, the spouseof the subjects with stroke (17-3%). Theremaining controls were obtained either byprobability sampling using a roster of neigh-bourhood residents obtained from Medicarefiles and a commercial list (53 0%), or fromneighbourhood volunteers (29 7%) who cameto our attention through advertising in thecommunity or by word of mouth. Weattempted to match controls to the subjectswith stroke by age. Baseline features of thestroke patients and controls are described in aprevious report.3 For the purposes of thisanalysis, nine controls were excluded (samplen = 240): eight were judged to be dementedbased on clinical features and neuropsycho-logical performance, and one had low testscores in the dementia range with a lifelonghistory of low intellectual attainment.

NEUROPSYCHOLOGICAL AND FUNCTIONALASSESSMENTSApproximately three months after the stroke,patients were given a battery of neuropsycho-logical tests, developed for the purpose ofdiagnosing dementia in a bilingual (Englishand Spanish), multiethnic, elderly populationas part of a broader epidemiological study ofdementia involving the Washington Heights-Inwood community surrounding the medicalcentre.67 We chose an interval of threemonths following onset for neuropsychologi-cal testing to allow sufficient time for theacute stroke effects to subside.89 Testing wasconducted in either English or Spanish,depending on the preferred language of thesubject, usually the language spoken at home.Neuropsychological functions assessed by thisbattery included six major cognitive domains:memory, both verbal (selective remindingtest'0) and visual (recognition task on theBenton visual retention test; BVRT"); orien-tation (orientation items from the mini mentalstate examination'2); language ability includingnaming (selected items from the Boston nam-ing test13), verbal fluency (controlled wordassociation test'4 and the category fluency

subtest of the BDAE5), comprehension (firstsix items of the complex ideation subtest ofthe BDAE5) and repetition (high frequencyitems from the BDAE5); visuospatial ability(five items selected from the Rosen drawingtest'5 and the matching task of the BVRT);abstract reasoning (similarities subtest of therevised Wechsler adult intelligence scale;(WAIS-R)'6 and the non-verbal similaritiesand differences subtest of the Mattis demen-tia rating scale'7); and attention (target detec-tion tasks'8). To examine attention, subjectswere given two separate cancellation tasksrequiring them to identify and mark specifictargets (either geometric shapes or lettergroups) as quickly as possible from an arrayof test stimuli, resulting in scores for errors,omissions, and total time to completion. Inaddition, to assess physical and non-physicalfunctional abilities, the Blessed functionalactivity scale'9 (BFAS), the Barthel index(BI),20 the stroke severity scale2' and theSchwab and England Scale22 were adminis-tered. The same neuropsychological batteryand functional examinations were adminis-tered to controls.

CLINICAL CLASSIFICATION OF STROKESUBJECTSBased on clinical findings during their stay inhospital, patients with stroke were classifiedby clinical syndrome and vascular territoryusing the methods of the Stroke Data Bank.2'Derived chiefly from neurological findings inthe acute phase of the stroke, the stroke syn-drome included six major types reflectinghemispheric laterality in relation to the pres-ence or absence of language versus spatialdeficits (dominant v non-dominant), severityof neurological impairment (major v minor),general cerebral location (hemispheric vbrainstem), and whether infarction wassuperficial or deep (lacunar v all others).Thus, the six syndromes were major domi-nant or non-dominant hemispheral, minordominant or non-dominant hemispheral,lacunar-deep infarction, and brainstem-cere-bellar infarction. For example, a patient witha transcortical motor aphasia, ideomotor dys-praxia, and severe, right hemiparesis withcrual predominance was classified as having amajor, dominant hemispheral syndrome indi-cating widespread damage in the anteriorcerebral artery. In contrast, a patient withanosognosia, left hemi-inattention and hemi-anopia, and left faciobrachial paresis was con-sidered to have a major, non-dominanthemispheral syndrome in the middle cerebralartery. Vascular territory was inferred fromthe neurological deficit profile and the topog-raphy of relevant infarction on brain imagingobtained during their hospital stay, if positive,using the guidelines provided by Damasio.2'Territories included internal cartoid, anteriorcerebral, middle cerebral, posterior cerebraland vertebrobasilar arteries. Classifications bysyndrome and vascular territory were inde-pendent of information on ii.uropsychologi-cal or functional testing. Based on anexamination of reliability among three raters

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in a subsample of 100 subjects, inter-rateragreement on stroke features was excellent,with K = 0-85 for syndrome and K = 093 forterritory.

DATA ANALYSIS AND STATISTICSMean scores of the stroke and control sub-jects on each of 17 scored items from theneuropsychological battery were comparedusing Student's two-tailed t test. To sum-marise the attentional tests, two indices werecalculated for both shape and letter targettasks: number of correct targets per second(total number of correct responses divided bytotal time taken to perform the test) andnumber of errors per correct response (ratioof errors to correct responses). The scoresfrom the shape and letter tasks were averagedto derive the two summary indices for eachpatient. Although the ages (mean (SD)) ofpatients with stroke and controls were com-parable (70-8 (7.9) v 70-6 (6 5)), the twogroups differed in other demographic factors:sex (% women, 52'9% v 65 8%), years ofeducation (10-2 (4 6) v 12-5 (4 4)) and race(% non-white, 65-2% v 47-1%). To adjust forthese factors in determining the frequency ofcognitive impairment, the raw test scores ofeach subject (total n = 467) were convertedto standardised residual scores, regressingdemographic variables (age, sex, race, educa-tion) with each of the 17 subtest variables.The resulting standardised residual score canbe considered to represent the differencebetween a subject's predicted and actual testscore. Following the approach of Rao et a124who studied cognitive dysfunction in multiplesclerosis, we used the fifth percentile of resid-ual scores of the control subjects as the cutoff for determining failure by patients withstroke on each item, which we used as thedefinition of cognitive impairment. As a sum-mary index of cognitive impairment, the totalnumber of failed tests for patients and con-

Table 1 Performnance of controls and subjects with stroke on neuropsychological tests(values are unadjusted means (SD)), and thefrequency ofstroke subjects (%) fallingbelow the fifth percentile based on standardised residual scores

Frequency (%/)Controls* Stroket ofstroke patients below

Neuropsychological test item (n = 240) (n = 227) fifth percentile

MemorySRT total 42-8 (10-6) 33-1 (11-5) 19-5SRT long term 29-5 (15-2) 18-7 (13-5) 10-2Delayed recall 5-9 (2-9) 4-2 (2-8) 18-1Delayed recognition 11-4 (1-3) 10-3 (2-2) 21-2Bentonrecognition 7-8 (1-8) 6-0 (2-2) 24-6

Orientation 9-7 (0-6) 8-6 (1-9) 25-8LanguageNaming 13-7 (1-7) 12-4 (2-7) 13-8CFL 11-7 (4-9) 7-4 (4-1) 14-4Category fluency 17-3 (4-9) 12-3 (4-8) 32-7Repetition 7-8 (0-5) 7-4 (1-1) 15-1Comprehension 5-5 (0-9) 4-8 (1-4) 13-3

Visuospatial skillsRosen construction 3-5 (1-0) 2-5 (1-2) 16-8Benton matching 8-8 (1-4) 7-3 (2-3) 25-0

Abstract reasoningSimilarities 10-7 (2-9) 8-2 (2-7) 16-1Identities 14-8 (1-6) 13-3 (2-2) 20-1

AttentionNo. correct/second 0-17 (0-08) 0-27 (0-09) 38-5No. errors/no. correct 0-29 (1-09) 0-05 (0-31) 20-2

*Mean age = 70-8 (7-9) years; mean education = 10-2 (4-6) years; 52-9% women; 65-2% non-white; tMean age = 70-6 (6-5) years; mean education = 12-5 (4-4) years; 65-8% women;47-1% non-white. SRT = selective reminding test; CFL = verbal fluency.

trols was also determined, again using thefifth percentile of performance by controlsubjects as the cut off for classifying a subjectas cognitively impaired. In addition, a'corrected' frequency rate of cognitive impair-ment in the patients with stroke was deter-mined by computing the difference inpercentage between patients with stroke andcontrols with cognitive impairment.

Patterns of cognitive impairment wereexamined using two approaches. Firstly, per-formance of stroke and control subjects wascompared on neuropsychological test itemsand by cognitive domains. The 17 individualscored items of the battery were entered intoa logistic regression model as independentvariables to identify tests which best corre-lated with stroke compared with control sta-tus. The six cognitive domains as definedabove were also examined in a separate logis-tic model. Impairment in a cognitive domainwas defined as defective performance in anyone or more of the items comprising thatdomain. The aim was to identify the neuro-psychological disturbances that were indepen-dently associated with ischaemic stroke overall,compared with subjects without stroke.Secondly, within the stroke cohort, we exam-ined the frequency of cognitive impairmentby clinical syndrome and vascular territory.The aim was to identify brain topographicalcorrelates of cognitive impairment.To determine whether our statistical

criterion defining cognitive impairment wasclinically relevant, we compared the charac-teristics of patients with and without cogni-tive impairment in relation to functionalimpairment (BFAS, BI, stroke severity,Schwab and England scale), and whether thepatient was independent after their stay inhospital (discharged home without assistance)or dependent (requiring either home atten-dant help or admission to a nursing home).As status at discharge is considered to be animportant measure of stroke outcome,25 wealso used a multiple logistic model to deter-mine whether the presence or absence of cog-nitive impairment was a significant predictorof dependent living after hospital admission,adjusting for the effects of physical impair-ment (BI 40 or less, as an indicator of lowfunctional ability25 26) and those sociodemo-graphic factors (age, sex, occupation, andmarital status) considered to influence dis-charge status.27 28

ResultsFREQUENCY OF COGNITIVE IMPAIRMENTComparing raw neuropsychological scores,patients with stroke were impaired on all 17scored items of the neuropsychological bat-tery (table 1). Adjusting for demographic fac-tors using standarised residual scores, theproportion of stroke subjects performingbelow the fifth percentile ranged from 10-2%to 38-5%. These proportions were differentfrom controls for each test item. The numberof failed tests (mean (SD)) differed sig-nificantly between patients with stroke

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70-

60

50

40

30

20

10

0mmI-

0 1 2 3 4 5 6 7 8

Number of Failed TestsFigure Frequency distribution of the number offailed neuropsychological test items inpatients with stroke (solid bars) and controls (hatched bars).

(3A4 (3 6)) and controls (0-8 (1-3)) (t (465) =

102, p < 0001). The frequency distributionof the number of failed tests for the twogroups is shown in the figure, indicating that78% of patients with stroke failed one ormore test items, compared with 40% of con-

trols. Using a cut off of four or more failedtests, 35-2% of patients compared with 3-8%of controls were classified as cognitivelyimpaired. As we did not require specific testsor domains for the definition of cognitiveimpairment, subjects with defective perfor-mance on four or more tests in a single cogni-tive domain-for example, language or

memory-might have been classified as

impaired, reflecting a circumscribed neu-

ropsychological defect. This did not occur,however, in any patient or control classifiedas cognitively impaired. The true or correctedfrequency of impairment associated withstroke was estimated by subtracting the "falsepositive" rate of the controls (5 0%), yieldinga proportion of 30-2%.

PATTERNS OF COGNITIVE IMPAIRMENT

Using a logistic model to identify the neuro-

psychological correlates independently associ-ated with stroke compared with control

Table 2 Logistic model of neuropsychological test items(model A, 17 total items examined) and cognitive domains(model B, 6 total domains examined) independentlycorrelated with stroke compared with control status

ModelANeuropsychologicaltest item SE p OR

Benton recognition 0-6297 0-1960 0-001 1 87Orientation 0-4351 0-2092 0-038 1-55Category fluency 0-7402 0-1905 <0-001 2-10Repetition 0-4761 0-2061 0 021 1-61Attention (correct/second) 0-8414 0-1859 <0 001 2-32

Model B

Cognitive domain SE p OR

Memory (verbal and visual) 0-4585 0-1270 <0-001 1-58Orientation 0-4158 0-2012 0 039 1-52Language 0-4252 0-1256 <0 001 1-53Attention 0-7523 0-1535 <0-001 2-12

,B = regression coefficient; SE = standard error of the mean-p = probability; OR = odds ratio.

Table 3 Clinical stroke features andfrequency ofcognitive impairment. Percentages indicate proportionswithin subject groups

Cognitive impairment n(%o)

Present AbsentStroke feature (n = 80) (n = 147)

Stroke syndromeMajor dominant 15 (18-8) 10 (6 8)Major non-dominant 12 (15-0) 5 (3-4)Minor dominant 10 (12 5) 25 (17-0)Minor non-dominant 10 (12 5) 30 (20 4)Lacunar 21 (26 3) 38 (25 9)Brainstem-cerebellar 12 (15-0) 39 (26-5)

Stroke ternitoryLeft ICA* 2 (2-5) 3 (2 0)Right ICA* 1 (1-3) 1 (1-4)Left ACA 5 (6 3) 3 (2 0)Right ACA 1 (1-3) 2 (1-4)Left MCA 24 (30-0) 33 (22 4)Right MCA 25 (31-3) 40 (27 2)Left PCA 6 (7-5) 6 (4-1)Right PCA 4 (5 0) 10 (6 8)Vertebrobasilar 12 (15-0) 48 (32 7)

*Borderzone infarction. ICA = internal cerebral artery;ACA = anterior cerebral artery; MCA = middle cerebralartery; PCA = posterior cerebral artery

status, impairment in the following tests wasmore likely to be associated with stroke (table2): Benton recognition, orientation, categoryfluency, repetition, and attention (number ofcorrect targets per second). The fi values andcorresponding odds ratios may be interpretedas the risk of impairment on those test itemsassociated with stroke compared with subjectsfree of stroke. When these test items weresummarized into cognitive domains, the mostsignificant areas of impairment were memory,orientation, language, and attention (table 2).

Confining the analysis to the stroke group,cognitive impairment varied by stroke syn-drome (2x p < 0.001). Patients with majordominant and major non-dominant syn-dromes were most likely to be cognitivelyimpaired (table 3), consistent with majorneurobehavioural effects from large infarc-tions. When cognitive impairment was exam-ined by specific vascular territory andlaterality (table 3), differences were less obvi-ous, in part because of small samples in someof the subgroups. Overall, cognitive impair-ment appeared most frequently with infarctsin the left anterior and posterior cerebralartery territories and least frequently withinfarcts in the vertebrobasilar artery territory.Examining vascular distribution indepen-dently of hemispheric side, the proportion ofinfarcts in the anterior cerebral artery terri-tory was higher among those with cognitiveimpairment (7 6%) compared with thosewithout (3.4%) (2, p = 0-053). Comparingleft-sided, right-sided and vertebrobasilarstrokes, left-sided damage was more commonamong those with cognitive impairment(46&3%) compared with those without(30-6%) (x2, p < 0.001).

RELATIONSHIP TO OTHER CLINICAL VARIABLESAND FUNCTIONAL STATUSAmong patients with cognitive impairment,women predominated, despite correction forsex in the regression model (table 4). Severityof functional impairment was significantlygreater with cognitive impairment, measured

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Table 4 General clinical andfunctional characteristics of stroke patients andfrequency ofcognitive impairment. Percentages indicate proportions between subject groups

Cognitive impairment n(%O)

Present AbsentCharacteristic (n = 80) (n = 147) p

Demographic factorsAge, mean (SD) 71-5 (7 8) 70 5 ( 7-9) 0-383Sex (%) 0-015Men 29 (27-1) 78 (72-9)Women 51 (42-5) 69 (57-5)

Race (%) 0-963Non-white 52 (35-1) 96 (64 9)White 28 (35 4) 51 (64 6)

Education, mean (SD) 10-4 (4 2) 10-1 (4 8) 0 651Screening tests of cognition and moodMMSE score, mean (SD) 21-7 (5 3) 26-4 (35) <0-001Short Blessed, mean (SD) 10-9 (7-1) 4-5 (5-1) <0-001HDRS, mean (SD) 5-5 (4-4) 4-5 (4-6) 0-096

Functional and physical impairmentBFAS, mean (SD) 3-8 (3 9) 1-5 (2 0) <0-001Barthel, mean (SD) 77-0 (27-9) 89-9 (17-8) <0-001Stroke Severity, mean (SD) 6-0 (3-2) 4-6 (3-2) 0-007Schwab and England, mean (SD) 66-0 (22-4) 80 3 (20 8) <0-001

Status after discharge (%) 0-001Independent 36 (26 7) 99 (73 3)Dependent 44 (47-8) 48 (52 2)

Student's t test for differences in means or X2 for differences in proportions.MMSE = Mini mental state examination; HDRS = Hamilton depression rating scale;BFAS = Blessed functional activity scale.

Table S Logistic model offactors independently correlated with dependent living (nursinghome placement or home attendant) following dischargefrom the hospital

/1 SE p OR

Age (main effect)* 0-00180+ years 1-6437 0-4631 < 0-001 5-1770-79 years 0-5560 0-3162 0-079 1-74

Barthel (<40 v 40+) 1-3127 0-6054 0-030 3-72Cognitive impairment 0-8766 0 3074 0-004 2-40Constant -1-2218 0-2433 < 0-001

*Compared with 60-69 years. f, = regression coefficient; SE = standard error of the mean;p = probability; OR = odds ratio.

by the BI, stroke severity scale, and theSchwab and England scale (table 4).Moreover, dependent living after discharge,either at home or nursing home, was morelikely (55 0% with, 32-7% without cognitiveimpairment, p = 0-001). In a logistic modelexamining the risks related to dependent liv-ing after stroke (table 5), cognitive impair-ment was a significant predictor (OR = 2-4;95% confidence interval, 1-3 to 4-4), afteradjusting for age (OR= 5-2, 80 + v 60-70years) and physical impairment (OR = 3-7,BI <40 v > 40). Marital status was border-line in significance, while sex and occupationwere not significantly related.

DiscussionIn this report, our intent was not to describethose circumscribed neurobehavioural syn-dromes that are well known after focal braininfarction29; nor did we directly examinedementia, which we have previouslydescribed in this sample, defined by the pres-ence of specific cognitive deficits in combina-tion using modified DSM-III-R criteria.'Rather, our aim was to focus on cognitiveimpairment as a general indicator of intellec-tual decline following ischaemic stroke,'0which we defined as failure on any four ormore neuropsychological test items using astatistical criterion based on normative datafrom a stroke-free sample.

Our approach raises several importantmethodological and conceptual issues inneuropsychological studies of patients withcerebrovascular disease. A fundamentalproblem, common to all studies usingpsychometric tests, is the definition of nor-mality compared with abnormality or impair-ment, a discrimination that depends in parton the reference group or standard selected.Four approaches have been typically used,including comparison with: premorbid ability;a non-clinical sample without the disorder orexposure; a clinical sample with the disorderor exposure; or predetermined cut off criteriabased on externally derived standards. Thefirst approach provides the most clinicallymeaningful information for the affected indi-vidual, even though impractical or difficult toestimate with accuracy; the last approach ispotentially the most arbitrary.We used the second approach, a com-

monly accepted method to define abnormal-ity which is perhaps least arbitrary, butsusceptible to biases related to subject vari-ables (age, education, sex, and race) knownto affect psychometric test performance inde-pendent of disease state." 32 After adjustingfor these factors, however, the frequency ofcognitive impairment in our elderly patientswas high, evident in approximately a third ofpatients examined three months afterischaemic stroke. A similar frequency ofimpairment in orientation (27% for"confusion or unassessable") and a figurecopying task (26% for "failed or unassess-able") was observed in a study of 470patients examined six months after stroke.2 Inanother related study, immediate logicalmemory (evaluated by recall of a story) wasdefective in 29% of 138 patients examinedthree months after stroke.33A further methodological and conceptual

issue pertains to the relationship of our defin-*ition of cognitive impairment to the diagnosisof dementia. In our analysis of deficit pat-terns, we found that cognitive impairmentvaried by stroke syndrome (most frequentwith large, dominant and non-dominantinfarcts) and vascular territory (most frequentwith dominant anterior and posterior cerebralartery territory infarcts, findings that weresimilar to the clinical correlations whendementia was used as the outcome.'4Moreover, when comparing patients withstroke with those without clinically evidentcerebrovascular disease, the cognitivedomains most likely to be defective werememory, orientation, language, and atten-tional functions. Defective memory and ori-entation are considered to be the clinicalhallmarks of dementia, and appear to be thebest psychometric discriminators of normalageing from dementia.'5 These findingstogether suggest that our definition of cogni-tive impairment identifies patients who areless severely affected within the spectrum ofintellectual decline, with dementia represent-ing the most extreme state. A further implica-tion arising from the identification of specificcognitive domains impaired with focal stroke

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is their potential relevance in screening forcognitive impairment or dementia amongpatients with stroke. For example, the minimental state examination, which we havefound to have acceptable sensitivity andspecificity as a dementia screen in cerebrovas-cular disease,36 contains test items that assessthose four domains.

Although we have circumvented the poten-tial problems of definitions posed by usingdementia as a diagnosis,4 our use of a statisti-cal criterion raises the question of clinical rel-evance. Based on our analysis of dischargestatus as an outcome, the presence of cogni-tive impairment significantly correlated withdependent living after admission to hospital(whether requiring nursing home or homeattendant care), even after adjusting for theeffects of age and physical impairment.Although this finding is neither novel nor

unexpected, it serves as an indirect validationof our approach and, more importantly,emphasises the potential value of neuropsy-chological assessment of patients with stroke.It is further consistent with our previous find-ing that poor performance on the mini mentalstate examination in the first week after acuteischaemic stroke is among the most importantpredictors of disability three months later.3Yet mental function tests have largely beenignored or limited in both observationaloutcome studies2' and interventional clinicaltrials aimed at minimising neurological dis-ability from ischaemic stroke." We thereforeconclude that cognitive impairment is notonly frequent with stroke, but also signifi-cantly affects functional adaptation after theacute phase. Efforts to modify the course ofacute stroke should also take into account"chronic brain failure"38 as an outcome.

The authors are indebeted to Ms Georgina Ferrer, LeslieHanzawa, RN, and Beth Rosenstein for their assistance in theclinical evaluation of our patients, and to Professors RichardMayeux and J P Mohr for their critical review of the manu-

script.This work was supported in part by Grants NS26179 andAG07232 from the National Institutes of Health, USA.

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3 Tatemichi TK, Desmond DW, Mayeux R, et al.Dementia after stroke: baseline frequency, risks, andclinical features in a hospitalized cohort. Neurology1992;42:1185-93.

4 Tatemichi TK, Desmond DW, Stem Y, Sano M, MayeuxR, Andrews H. Prevalence of dementia depends ondiagnostic criteria (abstract). Neurology 1992;42(Suppl.):413.

5 Goodglass H, Kaplan E. The assessment of aphasia andrelated disorders, 2nd edn. Philadelphia: Lea and Febiger,1983.

6 Stern Y, Andrews H, Pittman J, et al. Diagnosis of demen-tia in a heterogeneous population: Part I. Developmentof a neuropsychological paradigm and quantified correc-tion for education. Arch Neurol 1992;49:453-60.

7 Pittman J, Andrews H, Tatemichi T, et al. Diagnosis ofdementia in a heterogenous population: Part II.

Comparison on a paradigm-based diagnosis and physi-cian's diagnosis. Arch Neurol 1992;49:461-7.

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