Neuropsychological Evaluation in Adults with Epilepsy

Laura Renteria

Neil H. Pliskin

Neuropsychological assessment is an essential component of the evaluation and treatment of adults with epilepsy. A neuropsychological evaluation provides important diagnostic information about an individual’s cognitive strengths and weaknesses and can help clarify the presence of a psychiatric disorder. This is especially relevant in individuals with epilepsy, as they experience a higher prevalence of depression than the general population (1). Information gained from a neuropsychological evaluation also has important practical implications, including how specific drug treatments affect cognitive functioning and whether cognitive difficulties will interfere with the capacity to live independently and manage important activities, such as operating a motor vehicle and managing personal finances.

Neuropsychological assessment also plays a critical role in the preoperative evaluation of patients with medically intractable epilepsy who are candidates for surgery. The aims of the preoperative assessment are to help establish the laterality and localization of an epileptic focus and corroborate evidence garnered from electroencephalographic and radiological findings. The evaluation is further useful in determining a person’s cognitive baseline. This information may be used as a reference point for determining which patients may be at risk for significant memory or language decline after the proposed surgery. The reader is referred to Chapter 10 to learn more about the neuropsychological evaluation in epilepsy surgery.

The Neuropsychological Evaluation

A neuropsychologist is a doctoral-level psychologist who applies principles of assessment and intervention that are based on empirical research that examines the relationship between brain and behavior (2). A neuropsychologist evaluates patients through a clinical interview, behavioral observation, and a battery of validated paper and pencil tests. Through the clinical interview, a case history is developed that allows the neuropsychologist to generate hypotheses about the etiology of a patient’s symptoms. In turn, these hypotheses help to guide the interview and the plan for test administration. Behavioral observations help to determine if there are any limitations
that might influence test selection or interpretation such as motor, sensory, or visual deficits. Behavioral observations further allow the neuropsychologist to determine if there are any variables that may directly influence overall test performance, such as the patient’s level of alertness, confusion, motivation, and attention. Finally, observation of the patient may suggest an alternative explanation for a person’s test performance, such as anxiety, depression, thought disorder, or malingering.

Neuropsychological assessment is composed of standardized, objective measures that assist in determining the presence, nature, and severity of cognitive decline. Reliability in administration between patients and across settings is obtained through the use of standardized administration instructions and scoring procedures. The determination of cognitive decline is based on comparisons with a normative sample and estimates of premorbid intellectual function (3). The cognitive deficit observed is expected to be related to some underlying neuropathology. Later on, we will review the specific types of deficits seen in temporal lobe epilepsy (TLE) and frontal lobe epilepsy (FLE) in more detail.

The neuropsychological test battery varies by clinician, but is typically broad with regard to the abilities that are assessed. It usually includes tests of premorbid intellectual ability, intelligence, memory (visual and verbal), attention, problem solving, language processing, visuospatial processing, motor functioning, and emotional functioning. Certain measures tend to be used with some consistency and are listed in Table 10.1. Covering all of these cognitive domains allows for the differentiation of the temporal or frontal structures that may be affected. It is important to note that comparison across tests is sometimes problematic because of differences in each of the normative samples. These differences should be taken into account or, whenever possible, co-normed measures (i.e., tests given to the same population allowing for direct comparison of test findings) such as the Wechsler scales should be utilized.

TABLE 10.1 Commonly Used Adult Neuropsychological Measures

Premorbid intellectual ability
  Wechsler Test of Adult Reading (WTAR)
  National Adult Reading Test (NART)
Intelligence
  Wechsler Adult Intelligence Scale—Third Edition (WAIS-III)
  Wechsler Abbreviated Scale of Intelligence (WASI)
  Raven’s Progressive Matrices
  Test of Nonverbal Intelligence—Third Edition (TONI-III)
Memory
  Wechsler Memory Scale—Third Edition (WMS-III)
  California Verbal Learning Test—Second Edition (CVLT-II)
  Rey-Osterrieth Complex Figure
  Brief Visuospatial Memory Test—Revised (BVMT-R)
  Buschke Selective Reminding Test
Attention
  Digit Span
  Spatial Span
  Stroop Color Word Test
  Digit Symbol Coding
  Symbol Search
  Trail Making Test A and B
Problem solving
  Wisconsin Card Sorting Test
  Booklet Category Test
  Tower of London
  Delis-Kaplan Executive Function System (D-KEFS)
Language
  Boston Naming Test
  Controlled Oral Word Association Test (COWA)
  Token Test
  Animal Fluency
Visuospatial
  Block Design
  Ruff Figural Fluency
  Benton Facial Recognition Test
Motor
  Grooved Pegboard
  Finger Tapping
Emotional functioning
  Minnesota Multiphasic Personality Inventory—Second Edition (MMPI-II)
  Personality Assessment Inventory (PAI)
  Beck Depression Inventory—Second Edition (BDI-II)
  State Trait Anxiety Inventory (STAI)

Premorbid Intellectual Ability

One of the first goals of the neuropsychologist is to determine if a patient has experienced a change or decline in cognition that can be attributed to a central nervous system insult (3). Because patients rarely undergo a cognitive evaluation before their insult or injury, neuropsychologists must estimate their premorbid level of intellectual functioning. There are numerous ways to estimate premorbid cognitive function. First, certain reading and vocabulary tests are administered that have been posited to be
resistant to the effects of aging and/or brain injury (4). However, these types of tests can be problematic when a patient has suffered a brain injury that would adversely affect their performance on this type of test (i.e., aphasia). Second, because there are relatively high correlations between intelligence and educational/occupational achievement, these variables are frequently utilized to estimate premorbid ability levels (5). Regression equations employing these and other demographic variables can be used to estimate a person’s anticipated level of premorbid cognitive functioning (5). In addition, population-specific tables can assist in determining what an individual’s premorbid functioning may be, based on ethnicity, age, and educational attainment. With this method, a decline in cognition would be determined if the patient’s current performance fell significantly below the typical performance of his/her peers.

Intelligence

Intelligence testing assists the neuropsychologist by allowing him/her to observe how a patient performs on a wide array of tasks. In this way, the neuropsychologist may determine if there has been a global or domain-specific decline. In general, surgical candidates with TLE have been found to have IQ scores in the average range (6,7). Some epilepsy centers, however, have considered an IQ below 70 (borderline range) to be a contraindication for surgery as it suggests widespread damage and therefore poor localization of seizure onset (6). Intellectual impairment is often associated with an earlier onset of epilepsy, which is assumed to interfere with brain maturation and cognitive development (8). Postoperatively, a modest increase in IQ may be observed that may be due to improved functioning of the nonoperated hemisphere (9).

Memory and Learning

As individuals with epilepsy complain of memory difficulties more frequently than any other cognitive problem (6), an assessment of memory and learning is critical. The tasks administered typically require the patient to learn a series of words or pictures that are to be spontaneously recalled immediately and after a delay. To assist with differential diagnosis, the memory examination should assess the pattern of information acquisition, immediate recall, delayed recall, and recognition of information. Furthermore, these components should be evaluated for both verbal (i.e., word lists and stories) and nonverbal domains (i.e., geometric figures and human faces). As discussed in more detail later, a focus in the left temporal lobe is related to verbal memory impairment whereas a right temporal focus is related to visual memory difficulties.

Attention

Attention is a multidimensional construct that refers to arousal, as well as focused and sustained attention. Deficits in attention may impact performance on other tests, and therefore it is necessary that this domain be assessed. Furthermore, deficits in brief auditory attention are often seen in patients with FLE. Attention can be assessed by tasks that require the individual to ignore irrelevant information while attending to relevant input or through tasks that require rapid scanning and identification of target stimuli. It can be further examined through continuous performance tests that require the individual to pay attention for an extended period of time.

Problem Solving and Executive Functioning

Executive functioning refers to a broad group of skills that includes problem solving, planning and organization, alternating behavior in response to the environment, drive, initiating activities, divided attention, and mental flexibility. Impairment in executive functioning is commonly associated with damage to the frontal lobes. A problem-solving task commonly administered during
an epilepsy assessment requires the patient to move beads on pegs into a given position in as few moves as possible. Another common task requires the patient to sort cards printed with different designs according to a principle decided by the examiner. Without warning, the examiner changes the sorting principle and the examinee must shift his/her cognitive strategy accordingly. Deficits in executive functioning may lead to problems in organizing oneself to carry out activities of daily living, such as cooking and washing clothes. Moreover, deficits in executive function are least understood and appreciated by family members or friends, who may view the patient as lazy or unmotivated.

Language Functioning

Language functioning tests examine receptive and expressive language abilities. Some of the skills assessed include verbal expressive ability, naming, and comprehension. Determining the side of language dominance is important in a neuropsychological evaluation because atypical language dominance will influence interpretation of preoperative test findings and the prediction of cognitive outcome from surgery. Additionally, individuals with a focus in the left temporal lobe generally experience word-finding difficulties.

Visuospatial Functioning

There are numerous types of visuospatial abilities. Those that are assessed as part of an epilepsy examination include the ability to recognize faces, the construction of complex designs, spatial navigation, and the ability to discriminate and assess complex visual stimuli. Individuals with right hemisphere lesions generally perform poorly on these types of tests.

Motor Functioning

The motor examination consists of upper extremity tests that examine the speed by which hands can manipulate objects, write, or tap. Motor tasks are brief and easy to administer and tend to be minimally affected by education and intelligence quotient (IQ). This information helps to determine not only the speed of psychomotor processing but also lateralized dysfunction of the prefrontal cortex. Patients with FLE frequently demonstrate impairment in psychomotor processing speed.

Emotional Functioning

Emotional distress is not uncommon in individuals with epilepsy. They experience more depression and anxiety than the general population (10,11). An assessment of current and long-standing emotional and personality variables can prove useful in predicting which patients may experience more difficulty with surgical recovery. In fact, many epilepsy centers consider the presence of depression, psychosis, or personality disorder as contraindicative to surgery.

Assessment of mood is also critical for the interpretation of test scores, as it can influence test performance. Some researchers have found a relationship between depressed mood and decreased cognitive functioning across a wide range of neuropsychological domains (e.g., IQ, memory, executive functioning, language, and visuospatial skills) in patients with TLE (12). Therefore, understanding a patient’s emotional functioning can assist the neuropsychologist in determining whether there is objective cognitive impairment or if the observed deficits are due to emotional distress.

The most commonly employed measure of emotional functioning and personality characteristics is the Minnesota Multiphasic Personality Inventory—Second Edition (MMPI-II) (13). Research suggests that it is relatively insensitive to the influence of seizure symptoms and is reliable for assessing psychological functioning in patients with epilepsy (14). An advantage of using the MMPI-II over other assessment instruments is that it assesses test-taking attitude and profile validity. Further, the MMPI-II is helpful in obtaining information on clinically significant emotional distress, issues of
motivation, and facts relating to personality that may be relevant to treatment.

Interpretation of Neuropsychological Test Scores

Relating cognitive impairment to the lateralization and localization of the epileptic focus is an important part of the neuropsychological evaluation. Conclusions about epileptic focus should be based on convergence of data that includes neuropsychological test results, individual and family history, imaging results, medication effects, and personality. In TLE, lateralization is determined when there are consistent dissociations between performance on verbal and visuospatial memory tasks. It is more difficult to lateralize frontal seizure focus on the basis of neuropsychological tests (15).

Cognitive Impairment in Epilepsy

Problems with cognition are common in patients diagnosed with epilepsy. A recent survey revealed that 44% of patients with epilepsy complained of difficulty with learning and 45% felt they were slow learners (16). The focus of a seizure, including lateralization and localization, is an important factor in determining which cognitive abilities are likely to be effected (17). Seizure onset from the left hemisphere is likely to be associated with impaired verbal functions, including verbal memory and language deficits. In contrast, patients with a right hemisphere focus are more likely to display visuospatial deficits, including visual memory and constructional difficulties. In the next section, we review the research that has indicated the presence of specific cognitive deficits that assist in localizing individuals with TLE compared with those with FLE. It is important to note that atypical cerebral language reorganization may result from early seizure onset, which affects the lateralizing and localizing patterns on neuropsychological tests (18,19).

Temporal Lobe Epilepsy

TLE is the most frequent focal epilepsy. TLE is rarely controlled with medication, and therefore these patients are the most likely candidates for epilepsy surgery. According to histopathological studies, 70% of patients with TLE have hippocampal sclerosis (20,21). As a result, the leading complaint of patients with TLE is impairment in memory; however, the extent of impairment varies depending on the extent of damage to the hippocampi and adjacent temporal structures (20,21,22).

A focus in the left temporal lobe is related to verbal memory impairment (23,24,25,26,27,28) and word-finding difficulties (20). In addition, an association between an epileptic focus in the right temporal lobe and visual memory difficulties has been established (23,29,30,31,32,33,34). However, some research has demonstrated that individuals with right-sided epileptic activity do not demonstrate greater impairment on nonverbal memory tests when compared with patients with a left hemisphere focus (25).

Patients with TLE also often have cognitive deficits other than those related to learning and memory. Specifically, patients with TLE often exhibit executive dysfunction comparable to individuals with FLE (15,35,36). The reason behind executive dysfunction in TLE is unclear; however, some researchers posit that there may be propagation of seizures from the temporal to frontal lobes (36). This is considered to reflect the nociferous cortex hypothesis in which the negative effects of an active seizure discharge impair function at some distance away from the seizure focus (35). It is also possible that some extratemporal pathology is not detected with imaging (37) and/or that the hippocampus may serve some role in executive functioning (38,39).

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