J Neurol Neurosurg Psychiatry 1998 Royall 588 94

8/12/2019 J Neurol Neurosurg Psychiatry 1998 Royall 588 94

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CLOX: an executive clock drawing task

Donald R Royall, Je V rey A Cordes, Marsha Polk

AbstractObjective To describe a clock drawingtask (CLOX) designed to elicit executiveimpairment and discriminate it fromnon-executive constructional failure.Subjects 90 elderly subjects were studied(45 elderly and well persons from theindependent living apartments of a con-tinuing care retirement community and45 patients with probable Alzheimers dis-ease). The clock drawing performance of elderly patients was compared with that of 62 young adult controls. Methods Subjects received the CLOX,an executive test (EXIT25), and the minimental state examination (MMSE). TheCLOX is divided into an unprompted task

that is sensitive to executive control(CLOX1) and a copied version that is not(CLOX2). Between rater reliability (27subjects) was high for both subtests. Results In elderly subjects, CLOX sub-scores correlated strongly with cognitiveseverity (CLOX1: r =0.83 v the EXIT25;CLOX2: r =0.85 v the MMSE). EXIT25 andMMSE scores predicted CLOX1 scoresindependently of age or education(F (4,82)=50.7, p


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failures rather than ECF related failures, (2)bedside mental status examinations are eitherindirectly sensitive to ECF failures or ignorethem altogether, and (3) the possible qualita-tive di V erences in CDT failures arising fromtrue constructional as opposed to ECF relatedpathology are not routinely assessed. 20 Al-though several authors have commented on thesensitivity of CDTs to abstract thinking orcomplex behaviour, there have been noeV orts to grade the CDT as an executive task,nor to divorce the executive control of clockdrawing from drawing itself. We expect that asignicant proportion of the variance in CDTfailures is in fact the product of executive dys-control. In this paper, we describe a clockdrawing task which has been designed speci-cally to discriminate executive and non-executive elements.

MethodsSUBJECTS

The CLOX instrument was rst piloted in asample of 62 young adult undergraduates(mean age 24.4 (SD 4.3) years) attending theUniversity of Texas at San Antonio. This refer-ence group was compared with 90 elderly sub-jects, selected from two clinical settings. Fortyve were recruited from the independent livingapartments of a large retirement community.All were free of depression and self reportedimpairment in activities of daily living. Themean geriatric depression scale (GDS shortform) 21 score was 1.2 (SD 1.5). Scores >07/25are considered depressed. The mean inde-pendent activities of daily living score for thisgroup was 13.7 (SD 0.77). We further requiredthat these cases scored no less than 1.0 SDbelow the mean for 25 year old subjects on boththe verbal and performance subscales of theWeschler adult intelligence scale. This helps toassure us that the elderly control group is free

of incipient dementias. Less than 25% of inde-pendent living septuagenarians at this retire-ment community can pass this stringent crite-rion. Informed consent was obtained beforethe evaluation of both control groups.

The remaining 45 elderly subjects were out-patients diagnosed with probable Alzheimersdisease using National Institute of Neurological Communicative Disorders andStroke (NINCDS) criteria. 22 All hadundergone comprehensive geriatric assess-ments, including examination by a geropsy-chiatrist. Each received a history, physicalexamination, mental state examination, neu-

ropsychological testing, and functional statusevaluation. Clinical data were conrmed byfamily members or other available caregivers.All pertinent laboratory results and neuroimag-ing studies were reviewed. The patients withAlzheimers disease were further divided intothose with (n=19) and those without (n=26)gross constructional impairment on the minimental state examination (MMSE). Table 1compares these groups on selected clinicalvariables.

INSTRUMENTS

Subjects were interviewed by trained physi-cians using the CLOX, EXIT25, and MMSE.The CLOX was scored blind to the otherinstruments. Each instrument is briey de-scribed below.

The executive clock drawing task (CLOX)The CLOX has been divided into two parts tohelp discriminate the executive control of clockdrawing from clock drawing itself. The patientis rst instructed to draw a clock on the back of the CLOX form (see g 3). He or she isinstructed only to Draw me a clock that says1:45. Set the hands and numbers on the face sothat a child could read them. The instructionscan be repeated until they are clearly under-stood, but once the subject begins to draw nofurther assistance is allowed. The subjects per-formance is rated according to the CLOXdirections, and scored as CLOX1.

CLOX1 reects performance in a novel andambiguous situation. The patient is presentedonly with a blank surface and no furtherguidance regarding the task. He or she isresponsible for choosing the clocks overall form(a digital or analog face, alarm clock, wristwatch, or wall clock, etc), its size, position onthe paper, elements (hands, numbers, dateindicators), the forms of these elements (hands

as arrows, relative lengths, roman v arabicnumerals, etc). Furthermore, the patient mustalso initiate and persist in clock drawingthrough a sequence of constructional actions(usually drawing the outer circle, followed byplacing the numbers if any, followed by settingthe time). Finally, he or she must monitorprogress as the task unfolds, both anticipating(placing the 12, 6, 3, and 9 rst) and/ orcorrecting errors as they occur.

It is just as important to note what a patientdoes not do during a clock drawing task. OurCLOX form and its verbal instructions havebeen designed to distract the subject with

Table 1 Mean (SD) for selected clinical variables by group

Variable

Young adult controls(n=62)

Independent living retirees (n=45) Probable AD (n=45)

AD cases with MM SE constructional errors(n=19)

AD cases without MMSE constructional errors (n=26)

Age (y) 24.4 (4.3) 76.0 (11.6)* 75.8 (8.5)* 73.8 (9.2)* 76.5 (7.9)*Education (y ) 14.6 (1.2) 14.9 (2.2) 12.7 (2. 8)* *** 13. 4 (2.1)* * ** 12.2 (3.1)* ***EXIT25 4.2 (2.2) 8.8 (3.7)* 26.8 (7.5)* *** 31.1 (6.9)* *** 23.7 (6.3)***MMSE 29.3 (0.9) 29.1 (1.3) 16.4 (6.9)* *** 12.0 (6.7)* *** 19.7 (5.0)***CLOX1 13.2 (1.6) 12.1 (2.6)* 4.6 (4.5)* *** 2.1 (3.3)* *** 6.5 (4.4)***CLOX2 14.2 (1.2) 14.2 (1.0) 8.3 (5.3)* *** 3.4 (3.9)* *** 12.0 (2.4)***

AD=Alzheimers disease.*P


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strongly associated but irrelevant cues. Thecircle in the left lower corner is irrelevant toclock drawing when viewed from the reverseside of the form, but it tempts the patient toplace their clock within its image. We chose thewords hand and face because they aremore strongly associated with body parts thanclock elements, and may trigger semanticintrusions from their more common meanings.

The number 45 does not appear on a typicalclock face, and may intrude into the patientsconstruction in the form of a digital image(1:45) or hands pointing to the four or ve

oclock positions. CLOX scores range from015. Lower scores reect greater impairment.

The CLOXs second step is a simple copyingtask. The examiner allows the patient toobserve him or her drawing a clock in the circleprovided on the scoring sheet. The examinersets the hands again to 1:45, places the 12, 6,3, and 9 rst, and makes the hands into arrows.The patient is allowed to copy the examinersclock. This clock is scored as CLOX2. ThediV erence between CLOX scores 1 and 2 ishypothesised to reect the specic contributionof executive control versus visuospatial praxisto overall clock drawing performance assessedby CLOX1. Assuming that right parietal corti-cal function has not been compromised,lesionsto the frontal systems controlling clock drawingshould a V ect CLOX1 more than CLOX2.Thiscould occur in major depression, non-corticaldementias, or frontal type dementias that spareposterior cortical regions. If the right corticalhemisphere is a V ected, both scores should suf-fer.

Figure 1 presents the clock drawing per-formance of a non-demented elderly control

versus two demented patients who have beenmatched to their overall level of executive con-trol. Each patients pentagon drawing from theMMSE 23 has been included for comparison.Note that the pentagons in the MMSE areessentially a copying task that depends little onexecutive control.

Patient A is an independent elderly control.The presence of an essential tremor does notaV ect CLOX scoring. Patient B has Alzheim-ers disease. Clock drawing is impaired in bothunprompted and copy conditions. The MMSEhas an inherent bias towards cortical typedementia features. 24 This is reected byimpairment in patient Bs MMSE pentagonsand total MMSE score. Patient C has a vascu-lar dementia without cortical features. Only theunprompted clock drawing task is a V ected.This patients MMSE pentagons and totalMMSE score is within that instrumentsnormal range.

THE EXECUTIVE INTERVIEW (EXIT 25)

The EXIT25 is a bedside measure of executivecontrol. 25 26 It denes the behavioural sequelaeof executive dyscontrol and provides a stand-ardised clinical encounter in which they can beobserved. EXIT25 scores correlate well withother measures of ECF including the Wiscon-sin card sort ( r =0.54), trail making part B(r=0.64), the test of sustained attention (time,

r =0.82; errors, r =0.83) and Lezaks tinker toytest (r=0.57). EXIT25 scores also seem to cor-relate strongly with mesiofrontal cerebral bloodow by single photon emission computed tom-ography (SPECT). 27

EXIT25 scores range from zero to 50.Higher scores suggest greater impairment. Acut o V point of 15 out of 50 best discriminatesnon-demented elderly controls from both cor-tical and non-cortical dementing illness(SE=0.93, SP=0.83; area under receiver oper-ating curve (ROC), c=0.93). 28 An EXIT25 cutoV point of 10/50 best discriminates youngadults with and without mesiofrontal perfusion

Table 2 Pearson product moment correlations for selected clinical variables

Age Education EXIT25 MMSE CLOX1

Education 0.05EXIT25 0 .02 0.40*MMSE 0.05 0 .39* 0.92*CLOX1 0.08 0.36* 0.83* 0.82*CLOX2 0.10 0.24* 0.79* 0.85* 0.79*

*P5/50 impaired),MMSE=29/30 (scores


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decits after anterior cerebral arteryaneurysmectomy. 27 The EXIT25 is more sensi-tive than the MMSE to early cognitive impair-ment and non-cortical dementia in elderlysubjects. 24 26

THE MINI MENTAL STATE EXAM (MMSE )The MMSE is a familiar instrument. 23 It hasbeen criticised for insensitivity in early demen-tia, and poorly educated subjects. 28 In ourexperience, the MMSE is also selectivelybiased against the detection of isolated frontalsystem disease. 24 29 We hypothesise that in theabsence of posterior cortical type construc-tional impairment, CLOX scores will be moresensitive to dementia than the MMSE. TheMMSE was obtained blind to the subjectsEXIT25 and CLOX scores.

ResultsRELIABILITY

The internal consistency of the CLOX in thissample was high (Chronbachs =0.82). Itemtotal correlations ranged from r =0.32 to 0.77(mean r =0.41). No item improved Chron-bachs if removed. The CLOXs betweenrater reliability was determined in a subset of 27 elderly subjects. The subjects clocks wereexamined by two blind raters in the absence of clinical or demographic information. A highdegree of between rater reliability was found(CLOX 1: r =0.94, CLOX 2: r =0.93; bothp


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Figure 3

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because the combination of EXIT25 andMMSE scores, which takes much longer(2530 minutes) to administer, gave a less sat-isfactory performance (Wilkes lambda =0.73; F (2,34)=6.4; pexecutive impairment.

Cases in box C have signicant impairmentrelative to young adults on both CLOXsubscales. The regression line for the 45patients with NINCDS probable Alzheimers

disease enters this box from box A (g 2).Cases presenting above this regression linehave more executive impairment than would beexpected for an average Alzheimers diseasecase at that CLOX2 score. Cases presentingbelow this regression line would representgreater constructional impairment than couldbe expected for patients with Alzheimersdisease at similar CLOX1 scores. Figure 2 alsopresents the CLOX scores for the 45 elderlycontrols. It is immediately apparent that a sig-nicant fraction of this group (n=6, 14%) ispresenting in box B (with relatively isolatedexecutive impairment relative to both patientswith Alzheimers disease and young adult con-trols.

DiscussionIn this study we have shown that a clock draw-ing task can be constructed that is bothinternally consistent and strongly associatedwith an executive test measure. We can confirmthe impression of Huntzinger et al 33 that clockdrawing would be useful to clinicians in busyoutpatient practices. The CLOX is reliable,easy to administer, and well tolerated by elderlypatients. Because many elderly adults areresistant or non-compliant with formal at-tempts to document their cognitive perform-ance, a clock drawing assessment could im-prove testing compliance, especially in

outpatient, community, and residential settingswhere professional examiners are not available.We found that CLOX1 and CLOX2 scores

were strongly associated with both the EXIT25and MMSE. These associations persisted afteradjusting for age and education, although edu-cations range was limited by our sampleframe. 34 Construct validity is suggested by thending that the EXIT25 accounted for most of the variance in CLOX1 scores, after adjustingfor the MMSE, whereas the opposite wasfound for CLOX2 scores.

Subject performance on CLOX subscalesdisclosed interesting information about both

well elderly subjects and patients with Alzheim-ers disease. Signicant fractions of bothgroups presented below the fth percentile foryoung adult controls on one or more CLOXsubscales (n =37 (82%) of Alzheimers diseasecases; n =7 (16%) of controls). The pattern of these decits in Alzheimers disease suggests ageneralised dementing illness. Twentyseven(60%) patients with Alzheimers diseasefailed both CLOX subscales. By contrast, nocontrols presented below this threshold onboth subtests.

The cognitive impairments we found in wellelderly subjects suggest relatively isolated ECFimpairment. Six (14%) elderly controls failedonly the CLOX1 subscale, 12 (27%) failed theEXIT25 at 10/50. By contrast, only one elderlycontrol (2.2%) failed the MMSE at 24/30. AsAlzheimers disease a V ects posterior corticalregions before invading the frontal cortex, 35

isolated ECF impairment is not likely to repre-sent early Alzheimers disease. On the contrary,many non-Alzheimers disease medical disor-ders, including subcortical stroke, depression,polypharmacy, and hypothyroidism might be

expected to aV

ect ECFmore than posteriorcortical function. 18 20 The CLOX may provide apractical means to screen for these reversibledementias in community settings.

However, independent of these diseases,there are also reports of (1) isolated age associ-ated decline in ECF testing, 36 37 (2) dispropor-tionate frontal system atrophy on MRI, 38 and(3) disproportionate frontal system hypome-tabolism by SPECT in healthy elderly controlsrelative to young adults. 39 These studiessupport the phenomenological overlap be-tween well elderly subjects and those with iso-lated frontal system dementias. 40 41 The CLOXmay provide a means of detecting this condi-tion. In this study, only age, CLOX1, andEXIT25 scores discriminated between ouryoung and elderly control groups.

The CLOX2 subtest, like traditional cogni-tive tests, implicitly targets posterior corticaldecits. Recent studies suggest that differencesin right parietal metabolism discriminateAlzheimers disease subgroups with and with-out constructional impairment. 32 42 43 CLOX2scores discriminate Alzheimers disease sub-groups with and without gross constructionalimpairment, even after adjusting for severity of dementia, whereas the pattern of CLOX1/CLOX2 scores accurately classies 91.9% of patients with Alzheimers disease on this basis.

In this regard, our data are consistent with

those obtained by Sawada et al .44

They showedqualitative di V erences among patients withdementia for the pattern of SPECT perfusiondecits in the right parietal and frontal cortices.As we have noted, the patients with dementiadiV ered from elderly and young adult controlsin both indices. All patients with dementiashowed frontal cortical hypometabolism rela-tive to controls, but subsets among themdiV ered with in right parietal perfusion. Therelation of the CLOX to cortical pathology/perfusion has yet to be determined.

In summary, the CLOX is an internally con-sistent measure that is easy to administer and

CLOX: an executive clock drawing task 593



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displays good reliability between raters. It isstrongly associated with both MMSE andEXIT25 scores. The pattern of clock drawingfailures may be useful in the discrimination of clinically homogenous Alzheimers diseasegroups, or in the discrimination of Alzheimersdisease from non-Alzheimers disease cases.These issues remain to be explored in futurestudies.

We acknowledge the important cooperation and support wereceived from the Air Force Villages. This study was supportedby a grant from the Freedom House Foundation of SanAntonio, Texas, USA.

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doi: 10.1136/jnnp.64.5.588 1998 64: 588-594J Neurol Neurosurg Psychiatry

Donald R Royall, Jeffrey A Cordes and Marsha Polk CLOX: an executive clock drawing task

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J Neurol Neurosurg Psychiatry 1998 Royall 588 94

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