Measurement of cognitive function

Several criteria define the ideal test of cognitive function in epilepsy:

• both sensitive and specific for deficits produced by the disorder
• reproducible
• easily and quickly administered
• accepted as the standard by epilepsy researchers

Unfortunately, the tests and batteries most often used to evaluate cognitive decline in epilepsy do not meet any of these criteria. They have limitations, and their use varies. Often, familiar tests or tests that are tailored to prove certain hypotheses are selected, thus complicating the literature with inconsistency and inaccuracy.

Wechsler Adult Intelligence Scale–Revised (WAIS-R)

The Wechsler Adult Intelligence Scale–Revised (WAIS-R) is the most commonly used assessment of intelligence in epilepsy.8 This test evaluates 11 different abilities:9

Six verbal subtests:

• information
• comprehension
• similarities
• arithmetic
• digit span
• vocabulary

Five performance subtests:

• picture arrangement
• picture completion
• block design
• object assembly
• digit symbol

The average range of the WAIS-R intelligence quotient (IQ) is 90 to 110, with mental retardation being defined as an IQ of less than 70.

Neuropsychological testing

Neuropsychological testing often is used to evaluate cognitive and behavioral deficits. Although it often includes the WAIS-R, neuropsychological testing lacks a standard such as the WAIS-R.

The problems created by the lack of standardization are illustrated by a literature search to determine the number of neuropsychological tests used in randomized controlled trials of AEDs.10 In the 43 papers found, 87 different tests were administered. The most commonly used test was applied only 13 times. Administration of tests and methods of reporting results were not uniform, further compounding this inconsistency.

Nevertheless, neuropsychological evaluation is currently the standard for assessing cognitive function in epilepsy patients. No equivalent exists with regard to careful and comprehensive evaluation of behavioral functions. Although mood and thought disorder can be assessed with standardized inventories, other behavioral functions, such as ability to comprehend emotional signals and ability to function successfully in social settings, are not readily tested.

Test batteries such as the Halstead-Reitan and Luria-Nebraska are commonly used as comprehensive measurements of neuropsychological functioning.11,12 However, neither of these batteries was designed to assess the function of patients with epilepsy, and their use for this purpose can be misleading. For example, the Halstead-Reitan battery was designed for head-injured patients and those who have undergone lobectomy.10 In addition, neither of these batteries is truly comprehensive, and each one often fails to provide a detailed evaluation of specific deficits.13

Neuropsychological Battery for Epilepsy

The first attempt to create a test specific for the cognitive deficits of epilepsy was the Continuous Performance Test, in the 1950s.14 In 1978, Dodrill15 designed the Neuropsychological Battery for Epilepsy.15 He selected 16 tests on the basis of their ability to discriminate between normal subjects and patients with epilepsy and then performed an independent cross-validation assessment. In Dodrill’s battery, factors such as verbal and nonverbal memory, sustained attention, and verbal problem solving receive a more thorough treatment than they do in the Halstead-Reitan battery. The Neuropsychological Battery for Epilepsy also attempted to standardize component tests, gender differences, and selection of an appropriate control population.

Adoption of assessment protocols specific for epilepsy has been far from unanimous, however. In a review of 43 AED trials, only 2 used the Neuropsychological Battery for Epilepsy, and both were conducted by Dodrill and associates.10

FePsy

FePsy, a computerized assessment of neuropsychological functioning in patients with epilepsy, was developed by Alpherts and Aldenkamp.16 This system includes tests of simple reaction time, binary choice reaction time, tapping speed, visual searching, and recognition. The advantage to this system is that performance in patients can be tracked over time via a database, but the system is not comprehensive or widely used.

Adapted from: Devinsky O and Tarulli A. Progressive cognitive and behavioral changes in epilepsy. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;133–149.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.

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