Validation of the Wechsler Memory Scale-Revised in a sample of people with intractable temporal lobe epilepsy.

Abstract

The Wechsler Memory Scale-Revised (WMS-R) is used routinely for presurgical assessment of memory for patients considering elective resection of the temporal lobe and/or hippocampus for the relief of intractable temporal lobe epilepsy (TLE). We investigated the validity of the WMS-R in a population of people with TLE. The sample consisted of 138 patients with a diagnosis of TLE in which the epileptogenic focus was clearly and exclusively lateralized to either the right or left hemisphere. They underwent a complete neuropsychological examination as a routine part of their investigation for epilepsy surgery. Psychometric scores included in this study were: Wechsler Adult Intelligence Scale-Revised (WAIS-R) I.Q. scores, National Adult Reading Test Revised (NART-R) predicted-I.Q. scores, and WMS-R Memory Index and subtest scores. Multiple univariate analyses were performed. The group with left temporal focus had significantly lower Verbal Memory Index, Logical memory (both immediate and delayed), and Digit Span scores. Visual/Verbal discrepancy scores incorrectly identified most patients with right temporal focus. Analyses of a total group of people with epilepsy (i.e., mixed temporal, frontal, occipital and unknown foci) as compared with the normative sample indicated that the patient group scored significantly lower across all memory index scores and most memory subtests. Our results confirm that the WMS-R is capable of lateralizing to left hemispheric impairment but is more problematic in the assessment of right hemispheric impairment. The Visual/Verbal Memory Index discrepancy has questionable validity. People with epilepsy performed less well on the WMS-R than did the normative sample. The need for reliable and valid nonverbal tests of memory is therefore warranted.