Verbal IQ performance IQ differentials in traumatic brain injury samples

Transcription

1 Archives of Clinical Neuropsychology 17 (2002) Verbal IQ performance IQ differentials in traumatic brain injury samples Keith A. Hawkins*, Kirsten Plehn, Susan Borgaro Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA Accepted 19 September 2000 Abstract Several studies of head trauma utilizing the Wechsler Adult Intelligence Scale (WAIS) reported large sample differentials between verbal IQ (VIQ) and performance IQ (PIQ), leading some writers to claim that the VIQ is largely unaffected by traumatic brain injury (TBI), and that a superiority of VIQ over PIQ should be expected. In contrast, our review of Wechsler Adult Intelligence Scale-Revised (WAIS-R) studies indicates that although TBI sample PIQ means are often depressed relative to VIQ means, the differences are small and sometimes in the opposite direction. Possible reasons for the discrepancy between our WAIS-R review and those of an earlier review of WAIS studies are discussed. Clinically, the lack of a VIQ PIQ difference should never be used to infer that a TBI has not occurred. D 2001 National Academy of Neuropsychology. Published by Elsevier Science Ltd. Keywords: Verbal IQ; Performace IQ; Traumatic brain injury Two events are commonplace in neuropsychology: a referral for the assessment of traumatic brain injury (TBI) and the inclusion of the Wechsler Adult Intelligence Scale (WAIS, WAIS-R, or WAIS-III) within the resulting evaluation (Lezak, 1995; Matarazzo, 1972). Wechsler predicted that large differentials between verbal IQ (VIQ) and performance IQ (PIQ) scores would be found more commonly in pathological than normal samples (Wechsler, 1958); thus, comparisons between the two could shed light on the likelihood that a head injury has caused brain damage. Consistent with this, Farr, Greene, and Fisher-White s (1986) review of seven trauma studies utilizing the WAIS revealed mean PIQ scores that were typically and significantly lower than the sample mean VIQ, with, for example, five of the seven samples * Corresponding author. CMHC, Room 530, 34 Park Street, New Haven, CT 06519, USA. Tel.: ; fax: address: keith.hawkins@yale.edu (K.A. Hawkins) /01/$ see front matter D 2001 National Academy of Neuropsychology. PII: S (00)

2 50 Table 1 Differences between mean WAIS-R VIQ and mean PIQ in head trauma samples Sample characteristics Authors n and comments Crawford, Johnson, Mychalkiw, 233 All subjects required inpatient care and Moore (1996) (PTA M = 21.9 days). Guilmette, Dabrowski, mild (LOC < 30 min; PTA < 24 h) Kennedy, and Gnys (1999) and 33 moderate to severe injury; 32% negative on neuroimaging; 34% positive on neuroimaging; 34% no imaging undertaken or information unavailable. Johnson, Bigler, Burr, 64 Admitted to hospital with GCS of 14 or less and Blatter (1994) (M = 8.4). Kelly, Johnson, Knoller, 50 Normal toxicology screens at trauma Drubach, and Winslow (1997) admission (PTA M = 29.7 days; trauma admission GCS M = 10.6). Kelly et al. (1997) 52 Positive alcohol screens at trauma admission (PTA M = 41.2 days; admission GCS M = 8.2). Kelly et al. (1997) 17 Positive drug screens at admission (PTA M = 34.6 days; GCS M = 9.4). Kraiuhun, Shores, 25 MRI evidence of structural abnormality and Roberts (1996) required (7 subjects thereby excluded). Eighteen of twenty-five subjects had PTA of greater than 1 week. Time since injury (months) mean VIQ mean PIQ mean VIQ minus PIQ a approximately 1.6 b approximately 1.6 b approximately 1.6 b K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002) 49 56

3 Authors n Sample characteristics and comments Little, Templer, Persel, and Ashley (1996) VIQ n = 77; PIQ n = 80: reason for discrepancy not explained. Injury severity sufficient for entry into rehabilitation program. All subjects were male had PTA > 1 week; 8 had PTA 1 day to 1 week; 3 had PTA of 1 h to 1 day. Time since injury (months) mean VIQ mean PIQ mean VIQ minus PIQ a Mattis, Hannay, Plenger, and Pollock (1994) not reported Moore et al. (1993) 102 Traumatic brain injury Paniak, Silver, Finlayson, 71 PTA data available for 63 subjects (M = and Tuff (1992) days; median 18 days). Parker and Rosenblum (1996) 33 Whiplash due to motor vehicle accident Subjects all had a diagnosis of whiplash and many had... a minor unrecorded trauma to the head. Exclusions included inpatient treatment, unconsciousness greater than 5 min, skull fracture, cerebral hemorrhage, contusions or lacerations. LOC = loss of consciousness; PTA = posttraumatic amnesia; GCS = Glasgow Coma Scale. a VIQ minus PIQ is the sample mean VIQ minus the sample mean PIQ. b Testing occurred a mean of 49.8 days post injury for the combined Kelly et al. samples. K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002)

4 52 K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002) showing a differential greater than 10 points. Farr et al. (1986) concluded that in the head trauma clinical picture VIQ should be higher than PIQ, and, citing Farr et al. s review, Parker and Rosenblum (1996) stated that brain trauma generally spares VIQ relative to PIQ. There are, however, reasons to doubt the adequacy of these conclusions. The studies reported by Farr et al. (1986) included several conducted in the acute phase of recovery, and the two studies conducted significantly post injury (18 and 39 months) reported mean VIQ mean PIQ differences small enough to be neither statistically nor clinically significant at the level of the individual (1 of 2 points, the other 6.8). If large differentials are not typically seen beyond the recovery phase, VIQ PIQ comparisons would result in invalid inferences in many if not most cases tested some time after injury. To further examine the utility of VIQ PIQ comparisons in the assessment of TBI, we conducted a literature search for studies that included the WAIS-R, the revised successor of the WAIS, within the assessment battery. 1. Method A PSYCHINFO literature search was constructed for studies published in English from 1984 to 1999 using the combination of keywords Wechsler Adult Intelligence Scale with head injury/injuries, brain damage, closed head injury/injuries, and brain injury/ injuries. Of 51 obtainable studies of TBI within which the WAIS-R was employed, 10 reported both WAIS-R VIQ and PIQ data for adult samples greater than 10 subjects. One study reported data for three distinct samples, resulting in a total pool of 12 samples. Subgroups with lateralized lesions are identified within three of these samples. 2. Results All data are presented in Table 1. The samples were mostly comprised of severely injured but stable patients tested after considerable periods of recovery. Time since injury at assessment (unreported for one sample) ranged from 1.6 to 72.5 months, with seven samples reporting means beyond 1 year, and another a mean of 9.7 months post injury. No obvious relationship between VIQ PIQ differential and time since injury is apparent, with, for example, one sample tested a mean of 1.6 months post injury showing a difference of less than one point. Mean VIQ exceeded mean PIQ in 10 of 12 samples, but typically the difference was small, with samples comprised predominately of subjects post severe injury exhibiting differences ranging from 1.3 to 6.1 (Table 1). The sample reporting the largest differential (8.1; Parker & Rosenblum, 1996) was the only one totally comprised of minor injury cases; in contrast, another sample incorporating a reasonable portion of mild injury subjects displayed a reverse differential (mean PIQ>VIQ; Guilmette et al., 1999). In WAIS and WAIS-R studies of lateralized damage due to conditions such as stroke or tumor, the VIQ has frequently been found vulnerable to left hemisphere lesioning, and, usually to a greater extent, the PIQ to right hemisphere damage (Bornstein, 1983; Bornstein & Matarazzo, 1982; Kaufman, 1990; Warrington, James, & Maciejewski, 1986). Three studies

5 K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002) identified subgroups with lateralized focal (sometimes reported as mass ) lesions, but only two allow for investigation of the effect on VIQ PIQ. Somewhat consistent with expectations, Mattis et al. (1994) reported data showing that for 15 patients with right hemisphere damage, the mean PIQ was 9.8 points lower than VIQ, whereas for 19 patients with left hemisphere damage, the mean VIQ and PIQ were virtually identical. In contrast, Paniak et al. (1992) reported that the average VIQ for 11 patients identified by CT scans as having lesions on the left exceeded their average PIQ by 6.27 points, whereas 11 patients with right hemisphere lesions obtained a mean PIQ only slightly lower than mean VIQ (2.09 points). Data provided by these two studies for subgroups with bilateral lesions display a more consistent superiority of VIQ over PIQ than does their data for right hemisphere lesion groups. Mean PIQ was lower than mean VIQ for bilateral lesion groups in both studies (VIQ PIQ = 8.29 for Mattis et al., 1994; 4.44 for Paniak et al., 1992). Separate IQ data were not reported for samples with lateralized lesions in the third study (Guilmette et al., 1999). The mean PIQ for the overall sample exceeded mean VIQ by 1.5 points despite the presence of a greater proportion with right than left hemisphere lesions (12% versus 3% of total sample). This should not be overread, as several subjects had either not undergone neuroimaging (for lesion identification; 16% of sample) or lacked imaging information (18%), while the remaining subjects had negative findings (32%) or bilateral injuries (19%). 3. Conclusions When tested beyond the acute phase of recovery, patients who have suffered significant closed head traumas are unlikely to display a sizeable superiority of VIQ over PIQ. Accordingly, the absence of a VIQ PIQ differential several months post head injury does not allow for any inference regarding the likelihood that brain injury exists. Preliminary traumatic head injury data gathered with the latest revision of the WAIS, the WAIS-III, and presented within the Technical Manual for the test support this conclusion (Psychological Corporation, 1997). Twenty-two patients with initial Glasgow Coma Scale scores < 13 and with loss of consciousness exceeding 60 min tested 6 to 18 months post injury obtained a mean PIQ 5.1 points lower than their mean VIQ (Psychological Corporation, 1997). In contrast, their mean WAIS-III Processing Speed Index score (consisting of Digit Symbol Coding and a new subtest, Symbol Search) fell 16.2 points lower than their Verbal Comprehension Index mean, and 18.7 points lower than their Perceptual Organization Index mean. These WAIS-III data suggest that depressed PIQ scores following head trauma may in good part reflect the vulnerability of Digit Symbol to associated pathophysiological processes (Hawkins, 1998). Digit Symbol featured the lowest subtest mean for five of the six WAIS studies with subtest data reported by Farr et al. (1986), and was the second lowest for the sixth. WAIS-R studies reporting full subtest data show the same trend (Crawford et al., 1996; Guilmette et al., 1999; Little et al., 1996; Paniak et al., 1992). Despite the development of index scores, the WAIS-III continues to generate VIQ PIQ data and so it remains important that this issue be well understood. Our finding that the WAIS-R PIQ

6 54 K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002) is not significantly depressed relative to VIQ in TBI samples differs from conclusions drawn by Farr et al. (1986) and Parker and Rosenblum (1996) based upon Farr et al. s review of WAIS studies. One explanation could reside in the acuity of many of the samples reviewed by Farr et al. The more predominately language-mediated and overlearned nature of the verbal subtests may afford greater resiliency against the pronounced slowing and disorientation associated with the acute stages of brain injury. Note, however, that Dikmen, Machamer, Winn, and Temkin s (1995) prospective study of a large sample of head-injured patients with varying levels of injury leaves little doubt that the VIQ is also depressed by head trauma, in reasonable proportion to injury severity, and that focal lesioning does not account for this. Thus, any redressing of the balance between VIQ and PIQ over time should not be taken to mean that patients have returned to neuropsychological normality. Rather, a reduced differential more likely means that functions especially impacted in the acute phases have been relatively restored Diffuse versus focal lesioning Many researchers avoid studying trauma patients to see how specific brain regions relate to discrete cognitive functions, because the damage is usually extensive and diffuse due to the macroscopic and microscopic changes found throughout the brain (Gazzaniga, Ivry, & Mangun 1998). Any focal or mass lesions that do occur exist against this backdrop, especially in the common case of motor vehicle accident head trauma. Bilateral fronto-temporal injuries (due to the common mechanics of the injury and the structure of the skull) and diffuse white-matter injuries are common. At lower injury levels, this widespread damage appears to result in selective impairments in attention/information processing (and possibly in memory; Binder, Rohling, & Larrabee, 1997; Dikmen et al., 1995), but with increasing injury severity persisting deficits on a wide range of tests/functions arise (Dikmen et al., 1995). Emotional and personality changes are also common if not universal after severe TBI and may have a profound effect on the patient s life (Lezak, 1995). Consistent with the viewpoint that diffuse damage is the norm, we (along with the authors of many of the reviewed studies) sought to determine the differential sensitivity of the VIQ and PIQ to TBI rather than the lateralizing significance of VIQ PIQ differences. Although most WAIS-R TBI studies have not reported focal lesion data, it is unlikely that unreported or undetected lesions pose a threat to the general finding. Given the number of patients involved across these studies, any lesions such as may exist are likely to be balanced across the hemispheres. 2 At the same time, it does not seem likely that the picture of small sample mean VIQ PIQ differences is due to a canceling out of data between patients with focal left damage (and depressed VIQs) and patients with right hemisphere damage (and depressed 1 The propensity of the PIQ to show a larger practice effect than the VIQ (Hawkins & Sayward, 1994) must be taken into account when considering repeat-testing data. 2 All studies (but one) failed to find a sizeable mean VIQ PIQ differential, so even if there were a bias within a single study, it has had no influence on the thrust of the overall data. The one study showing a moderate differential, Parker and Rosenblum (1996), was of patients least likely to have suffered serious brain injury of lasting consequence. This study of whiplash excluded subjects with unconsciousness exceeding 5 min or with contusions, lacerations, skull fracture, or cerebral hemorrhage.

7 K.A. Hawkins et al. / Archives of Clinical Neuropsychology 17 (2002) PIQs). The two studies reporting data for groups with lateralized focal lesions do not provide compelling evidence of a differential relationship thereof to VIQ PIQ in TBI. One obvious consideration is that the documentation of lesions on one side of the brain does not preclude the existence of damage elsewhere. As discussed, diffuse (if microscopic) damage also likely exists in these cases and may exert a greater influence on the behavioral picture. None of the preceding should obscure the fact that large VIQ PIQ differentials (in either direction) will be seen in head trauma cases, and, when so, will be of interest to the neuropsychologist. Although the WAIS/WAIS-R is an imperfect localizing or even lateralizing instrument (Warrington et al., 1986), the presence of a significant differential could draw attention to weaknesses that may reflect focal lesioning, fostering the generation of hypotheses to be tested with other instruments. In addition, the WAIS profile may contribute to rehabilitation and placement planning, and facilitate decision making regarding issues such as return to employment. The generation of factor-based index scores with the WAIS-III enhances the neuropsychological utility of the instrument, with the new Processing Speed Index showing particular promise with regard to TBI (Hawkins, 1998). Overall, however, the limitations of VIQ PIQ comparisons as a source of inference regarding the sequelae of TBI serves to remind us of the value of the comprehensive neuropsychological exam. References Binder, L. M., Rohling, M. L., & Larrabee, G. J. (1997). A review of mild head trauma: Part I. Meta-analytic review of neuropsychological studies. Journal of Clinical and Experimental Neuropsychology, 19 (3), Bornstein, R. A. (1983). Verbal IQ performance IQ discrepancies on the Wechsler Adult Intelligence Scale- Revised in patients with unilateral or bilateral cerebral dysfunction. Journal of Clinical and Consulting Psychology, 51, Bornstein, R. A., & Matarazzo, J. D. (1982). Wechsler VIQ versus PIQ differences in cerebral dysfunction: a literature review with emphasis on sex differences. Journal of Clinical Neuropsychology, 4 (4), Crawford, J. R., Johnson, D. A., Mychalkiw, B., & Moore, J. W. (1996). WAIS-R performance following closedhead injury: a comparison of the clinical utility of summary IQs, factor scores, and subtest scatter indices. Clinical Neuropsychologist, 11 (4), Dikmen, S. S., Machamer, J. E., Winn, R. H., & Temkin, N. R. (1995). Neuropsychological outcome at 1-year post head injury. Neuropsychology, 9 (1), Farr, S. P., Greene, R. L., & Fisher-White, S. P. (1986). Disease process, onset, and course and their relationship to neuropsychological performance. In: S. B. Filskov, & T. J. Boll (Eds.), Handbook of clinical neuropsychology, (pp ). New York: Wiley. Gazzaniga, M. S., Ivry, R. B., & Mangun, G. R. (1998). Cognitive neuroscience. New York: W.W. Norton. Guilmette, T. J., Dabrowski, J., Kennedy, M. L., & Gnys, J. (1999). A comparison of nine WAIS-R short forms in individuals with mild to severe traumatic brain injury. Assessment, 6 (1), Hawkins, K. A. (1998). 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. Clinical Neuropsychologist, 12 (4), Hawkins, K. A., & Sayward, H. (1994). Examiner judgment and actual stability of psychiatric inpatient intelligence quotients. Clinical Neuropsychologist, 4, Johnson, S., Bigler, E., Burr, R., & Blatter, D. (1994). White matter atrophy, ventricular dilation, and intellectual functioning following traumatic brain injury. Neuropsychology, 8 (3), Kaufman, A. S. (1990). Assessing adolescent and adult intelligence. Needham Heights, MA, USA: Allyn & Bacon.

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