Military Medicine: Wechsler Adult Intelligence Scale-Third Edition Characteristics of a Military Traumatic Brain Injury Sample

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Wechsler Adult Intelligence Scale-Third Edition Characteristics of a Military Traumatic Brain Injury Sample

Clement, Pamelia F

This article describes the postinjury cognitive functioning of a sample of active duty, retired, and military beneficiaries who received traumatic brain injuries. Patients were seen in the neuropsychology clinic at Brooke Army Medical Center for a detailed cognitive and personality assessment. The scores on a major component of this evaluation, the Wechsler Adult Intelligence Scale, third edition, are summarized. The results are compared with those reported in the Wechsler Adult Intelligence Scale, third edition technical manual for a smaller, less diverse sample. The findings are consistent with the formulation that stable verbal skills are most resistant to brain injury, followed by nonverbal reasoning and visuospatial ability, and then working memory with speed of information processing being the most vulnerable to the effects of brain injury.

Introduction

The incidence and characterization of individuals experiencing a traumatic brain injury (TBI) are of particular relevance to the military. Adolescent and young adult men are at increased risk for TBI, making the active duty military population a particularly vulnerable group.1 TBI among active duty troops account for at least 14% of surviving war casualties and require a disproportionate amount of acute and long-term care resources (http://www.biausa.org/Pages/For%20Military%20%26%20Veterans.html).2 The sequelae of severe brain injuries often lead to retirement and separation from the military on medical grounds. Even after mild TBI, subtle deficits in thinking and judgment can affect duty performance, rank advancement, and worldwide qualification status.

In the military setting, clinical neuropsychologists are responsible for cognitive evaluations of brain-injured patients. The Wechsler Intelligence Scales have long been a cornerstone of such evaluations. In 1997, the Wechsler Adult Intelligence Scale, third edition (WAIS-III), became available for use.3 With the previous edition of the WAIS, neuropsychologists were able to determine verbal intelligence quotient (IQ), performance IQ, and subtest scores. In the newer WAIS-III, subtests are also grouped into four indexes based on factor analysis. Scores on these indexes would appear to provide the neuropsychologist with an opportunity for a finer-grained analysis of intellectual functioning after TBI. This study presents WAIS-III IQ, index, and subtest scores for 61 active duty and military health care beneficiaries who were referred to the neuropsychological service of a major military medical center subsequent to a TBI. Severity of the TBIs ranged from mild through severe. The relationship of these scores to the individual's demographic characteristics and severity of the brain injury is examined. These data supplement those presented in the WAIS-III technical manual for a small group (N = 22) of moderate to severe TBI cases.4

Methods

Patients

A retrospective chart review was conducted on 61 adult military service members and military dependents that received outpatient neuropsychological evaluation at Brooke Army Medical Center in San Antonio, Texas. The sample selected for study was composed of individuals evaluated between June 1998 and June 2001 with a primary diagnosis of TBI. The final sample of 61 was reached after excluding a few cases because of the presence of confounding diagnoses, such as anoxia and cerebrovascular disorders. Reasons for referral included assessment of reported deficits, documentation of cognitive impairments, evaluation for return to duty determination, and medical board review for military separation. Table I presents the sample characteristics on basic demographic variables.

The present group is more racially heterogeneous than the TBI standardization sample reported in the WAIS-III manual. Whereas the standardization sample was entirely Caucasian, the present sample is approximately 60% Caucasian, 20% African American, and 20% Hispanic and other. Consistent with the demographics of both TBI and military populations, the present sample included proportionately more men (88% compared with 64% in the standardization sample). Age and education are relatively equivalent for the standardization and present samples. It can be seen in Table I that over one-third of the sample was undergoing medical/physical evaluation board process at the time of evaluation. Approximately one-third was on temporary disability leave, and slightly less than one-third was serving on active duty.

As shown in Table II, compared with the clinical TBI standardization sample, the present sample was more heterogeneous in terms of severity of injury and time since injury. The standardization sample included only individuals who had an initial Glasgow Coma Scale score less than 13 and loss of consciousness of at least 60 minutes, excluding all mild TBI cases. The standardization sample was evaluated between 6 and 18 months after injury, whereas the present sample included cases evaluated from 1 to 204 months after injury. Over one-half of the present cases incurred TBI from a motor vehicle accident. Other major causes of TBI in the current sample included falls and assaults, each accounting for 15% to 20% of the injuries.

Procedure

Demographic and injury information were collected at the time of the neuropsychological evaluation from medical records and interviews with the participant and, when possible, a family member. Classification of severity of TBI as mild, moderate, or severe was determined using available medical record information. Mild TBI cases had loss of consciousness less than 60 minutes and no neurological findings. Cases with loss of consciousness between 1 and 24 hours or significant neurological findings, even if the loss of consciousness was somewhat less than 60 minutes, were classified as moderate. Severe cases were those hospitalized for several days or longer with documented neurological damage and prolonged recovery.

The WAIS-III was administered and scored according to standard procedures by either a psychologist in postdoctoral fellowship training or a trained neuropsychological technician. WAIS-III scores analyzed in this study included age-corrected scaled scores on 13 subscales (omitting the Optional Object Assembly Subtest), four index scores (Verbal Comprehension Index [VCI], Perceptual Organization Index [POI], Working Memory Index [WMI], and Processing Speed Index [PSI]), and three IQ scores (full-scale, verbal [VIQ], and performance [PIQ]). Statistical comparison between VIQ and PIQ scores was done using a within-subjects Student's t test. Comparisons among the four index scores were made using an overall one-way within-subjects analysis of variance followed by individual pairwise comparisons using within-subjects Student's t test.

Results

Table III presents summary statistics for WAIS-III scores. No evidence of global impairment of IQ scores was seen for the sample as a whole. Average VIQ score of 103.6 was significantly higher than the average PIQ score of 99.6 (t = 2.72; df = 60; p = 0.008). The four mean WAIS-III index scores differed significantly (F = 18.86; df = 3; p

Table IV presents WAIS-III IQ and index scores separately for mild, moderate, and severe TBI groups. Age-corrected scaled scores on WAIS-III subscales for mild, moderate, and severe TBI groups are shown in Table V. WAIS-III scores for the three seventy groups are quite similar. Because of small sample sizes within the severity subgroups, statistical comparisons of WAIS-III scores across groups were not possible.

Discussion

The findings of this study suggest that the revisions seen in the WAIS-III can enhance its value as a neuropsychological instrument in a TBI population. In particular, the four WAIS-III indexes provide a finer-grained analysis of cognitive functioning than do the VIQ and PIQ scores in themselves. In this study, there was a statistically significant difference between VIQ and PIQ scores, although the actual means differed by only approximately 4 points. Traditionally, the VIQ has been considered a measure of stable verbal skills, whereas the PIQ as an indicator of fluid reasoning skills has been thought to be more vulnerable to brain injury.5 This assumption has recently been questioned in a review of 10 studies that found VIQ to be only slightly higher than PIQ in TBI populations.6 Although present findings reveal a statistically significant difference between VIQ and PIQ scores, the difference was clinically modest. These findings support the view that PIQ is more vulnerable to brain injury than VIQ but with variability across patients and clinically small overall group differences.

The WAIS-III verbal subtests can be looked at in terms of the VCI and the WMI as opposed to a monolithic VIQ. Similarly, the performance subtests can be broken down into the POI and PSI. In the current sample, the VCI had the highest mean score, followed by the POI, the WMI, and the PSI. These findings are consistent with the formulation that stable verbal skills are most resistant to brain injury, followed closely by nonverbal reasoning and visuospatial ability, and then working memory with speed of information processing being the most vulnerable to the effects of brain injury. In terms of subtest scores, digit symbol appears to be most sensitive to the effects of TBI.

Prior research suggests that the WAIS-III PSI score is a sensitive indicator of cognitive function. Lower PSI scores characterized all clinical groups in the standardization samples of the WAIS-III.7 In a study using profile analysis with WAIS-III index scores, subgroups were formed based on both overall level of WAIS-III performance and on a pattern of scores represented primarily by low or high score on the PSI.8 Another recent study found a large effect size of PSI score when comparing mild TBI, moderate-severe TBI, and control groups.9 TBI patients in another study showed slowing on the WAIS-III digit symbol subtest (one of the two major subtests loading on the PSI) at 1-week after injury compared with patients with mild non-neurological injuries.10 Taken together, all of these results support the idea that processing speed is a sensitive indicator of global brain function and efficiency after TBI.

Not only is processing speed often poorer than other cognitive functions after TBI, but there is also evidence suggesting that its recovery is prolonged. In a study developing a mathematical model for recovery from TBI based on duration of coma and WAIS-R scores, PIQ, a major component of which is processing speed, was over four times slower to recover than VIQ.11 Present results reinforce this concept in that our sample was tested an average of almost 3 years after injury, yet PSI scores were significantly lower than scores on the other WAIS-III indexes. In summary, present results indicate that global intelligence is relatively unaffected after TBI. They reinforce prevailing research showing that speed of information processing is particularly vulnerable to brain injury across a range of severity and time after injury.

References

1. Goldstein M: Traumatic brain injury: a silent epidemic. Ann Neural 1990, 27: 327.

2. Brain Injury Association. Available at http://www.biausa.org/Pages/ For%20Military%20%26%20Veterans.html; accessed January 2002.

3. Wechsler D: Wechsler Adult Intelligence Scale. Ed 3. San Antonio. TX, The Psychological Corporation, 1997.

4. WAIS-III WMS-III Technical Manual. San Antonio, TX, The Psychological Corporation, 1997.

5. Farr SP, Greene RL, Fisher-White SP: Disease process, onset, and course and their relationship to neuropsychological performance. In: Handbook of Clinical Neuropsychology, pp 213-53. Edited by Filskov SB, Boll TJ. New York, Wiley, 1986.

6. Hawkins KA, Plehn K, Borgaro S: Verbal IQ-performance IQ differentials in traumatic brain injury samples. Arch Clin Neuropsychol 2002; 17: 49-56.

7. Hawkins KA: Indicators of brain dysfunction derived from graphic representations of the WAIS-III/WMS-III technical manual clinical samples data: a preliminary approach to clinical utility. Clin Neuropsychol 1998; 12: 535-51.

8. Donders J, Zhu J, Tulsky D: Factor index score patterns in the WAIS-III standardization sample. Assessment 2001; 8: 193-203.

9. Fisher DC, Ledbetter MF, Cohen NJ, Marmor D, Tulsky DS: WAIS-III and WMS-III profiles of mildly to severely brain-injured patients. Appl Neuropsychol 2000; 7: 126-32.

10. Ponsford J, Willmott C, Rothwell A, et al: Factors influencing outcome following mild traumatic brain injury in adults. J Int Neuropsychol Soc 2000; 6: 568-79.

11. Wong PP, Monette G, Weiner NL: Mathematical models of cognitive recovery. Brain Inj 2001; 15: 519-30.

Guarantor: Pamelia F. Clement, PhD

Contributors: Pamelia F. Clement, PhD*; Jan E. Kennedy, PhD[dagger]

* ABPP, Brooke Army Medical Center, Fort Sam Houston, TX 78234-6200.

[dagger] Defense and Veterans Brain Injury Center, Wilford Hall Air Force Medical Center, San Antonio, TX 78227.

This manuscript was received for review in February 2002. The revised manuscript was accepted for publication in February 2003.