Epilepsy and Neuropsychology
Michael Westerveld, Ph.D., Assistant Professor, Department of Neurosurgery, Yale University School of Medicine, New Haven, CT.
Periodic self-examination is as important to the evolution of a professional discipline as it is to self improvement. A recent health care conference held for the benefit of insurers necessitated an updated description of the ways in which neuropsychology can contribute to the current and future care of epilepsy patients. The question of how neuropsychology benefits a patient with seizures underlies the more economically based question "Why should we pay for a neuropsychological assessment?" A cogent, practical description of the applications of neuropsychology in the context of a comprehensive epilepsy care model demonstrates the benefits to patients, caretakers, physicians and insurers.
Neuropsychology, broadly defined, is the application of psychological principles to the study and understanding of neurological underpinnings of human behavior. The neuropsychology of epilepsy is a subspecialty devoted to the understanding of disturbed brain behavior relationships and treatment of cognitive and behavioral symptoms which accompany seizure disorders. Most practitioners of neuropsychology hold advanced degrees in clinical psychology. This is supplemented with specialized training in neuropsychology at the postdoctoral level, including intensive didactic and applied clinical experiences. The integration of knowledge from a multidisciplinary background results in a unique understanding of the cognitive, social and psychological problems facing patients with epilepsy.
The neuropsychological examination of patients with epilepsy involves objective assessment of various cognitive and affective domains. There is no single instrument or battery of tests which is considered ideal for such an assessment, although several have been proposed (e.g., Neuropsychological Battery for Epilepsy, Dodrill, 1978). Many neuropsychologists prefer a combination of individual tests that assess the relevant abilities. These include measures of motor speed and dexterity, visual perception, visual-motor integration, speech and language processing, verbal expressive ability, verbal and visual memory, intelligence, executive functions, personality, and emotional and psychosocial functioning. As one might imagine, a comprehensive neuropsychological examination is time and labor intensive for the subject and clinician. However, the results provide valuable information about the overall status of the patient and facilitate treatment.
Functional status as barometer of disease severity and progression
For some patients with epilepsy, seizures result in failure to develop important social and vocational skills, while others suffer from the loss of previously acquired skills. Deficits may be related to impaired neurological function, or may be the result of psychological and social factors such as low self-esteem or stigmatization of the individual with seizures. The difficulties faced by a patient with chronic epilepsy develop over time, often in concordance with the evolution of the seizure disorder. Neuropsychological examination provides an objective index of patient functioning, which is used to document changes in status and modify treatment strategies accordingly.
Cognitive deficits such as learning disabilities, attention disorders, and developmental language disorders may appear in children with epilepsy. As the patient matures into adolescence and the seizure disorder evolves, deficits in memory and executive functions (e.g., organization, self-monitoring) may become more prominent, impacting on academic achievement and vocational preparation. Also in adolescence, psychosocial deficits appear. Poor self-esteem and fewer relationships with peers are common in adolescents with epilepsy. These factors often interact with treatment variables to produce a complex symptom picture in any given individual. Determination of the relative contribution of medication, substrate, and emotional/psychosocial effects permits more effective allocation of effort in treatment. Early assessment facilitates identification of the exact nature of a child's difficulties, and allows for more informed formulation of intervention strategies, minimizing the long-term impact of seizures. Even in adults, seizure disorders are rarely static. Patients may report ambiguous or diffuse changes in functioning, which can be more precisely defined with neuropsychological assessment. New onset impairments in cognitive function may signal the need for changes in medication, either because of toxicity or increased seizure activity. Abilities such as attention and concentration are often cited by patients as side effects of medication, but may be difficult to assess at bedside or in clinic. Neuropsychological examination is useful for detecting subtle changes in cognitive functions that are otherwise difficult to quantify.
Evaluation of treatment efficacy and risks
The primary treatments for epilepsy are pharmacological and surgical. Most patients enjoy adequate seizure control with medication treatment, and are productive in their social and vocational pursuits. However, patients who have seizures that are difficult to control and have a single, identifiable focal onset with characteristic ictal manifestations may benefit from surgery. While the primary goal of both treatment modalities is the reduction or elimination of ictal events, seizure reduction without concomitant improvement in functional status and patient quality of life is of questionable value. Implicit in the goal of seizure reduction is the return of the patient to a satisfactory, productive life while minimizing risks.
Seizure medications and cognition
Treatment with AEDs may be associated with changes in cognitive functioning that are independent of the cognitive impact of the seizures themselves. There have been numerous studies of the cognitive effects of AEDs, and several reviews of these studies. It is generally agreed that polytherapy (i.e. more than one AED) increases the risk to cognitive functioning; however, the impact of individual AEDs is less clearly defined. The greatest risk to cognitive functioning in monotherapy is toxicity.
The abilities affected by AED treatment may be behavioral, emotional, or cognitive, and may vary for different populations (e.g., children vs. adults; by seizure type; by level of cognitive impairment). Some AEDs may produce aggressive behavior in children with moderate developmental delay. As noted above, commonly cited side effects in children and adults are changes in attention and concentration. However, seizures themselves may be associated with impaired cognitive or behavioral development. It may be particularly useful to obtain information about baseline cognitive and behavioral status when initiating or changing medication treatment, in order to determine when unacceptable behaviors are side effects of treatment as opposed to developmental issues. Adverse reactions to medications are most often transient and easily remediated by changes in the medication regimen. However, more pervasive developmental issues require a different approach.
Epilepsy surgery
Patients with debilitating seizures may be considered candidates for epilepsy surgery. Focal resection of the epileptogenic region may be associated with both positive and negative effects on cognitive functioning. When the surgical resection includes functional cortical tissue, deficits in abilities mediated by areas in, and proximal to, the zone of resection may be anticipated. However, functions mediated by cortex distal to the planned resection may improve following surgery. A commonly cited example of this phenomenon is observed in temporal lobectomy. When seizures originate from the temporal lobe in the language dominant hemisphere, there is a risk to verbal memory and language functions such as naming. However, patients often demonstrate improvement in functions which are typically mediated by the nondominant hemisphere, such as visual memory and nonverbal reasoning. Understanding the patient's preoperative neuropsychological profile aids in counseling the patient about the anticipated outcome and facilitates identification of appropriate candidates for surgery.
Patient selection for surgery
Neuropsychological assessment is a noninvasive means of establishing evidence of focal dysfunction in candidates for epilepsy surgery. This is among the most widely recognized contributions of neuropsychology to epilepsy treatment. Seizures are well known to have an impact on patients' memory, and specific impairments in memory with relatively well preserved intellectual functioning point to temporal lobe involvement in seizure onset. Assessment of clinical memory in the context of a comprehensive neuropsychological assessment is considered an integral component of any epilepsy surgery evaluation (NIH conference).
Specialized procedures for predicting functional risk in epilepsy surgery
Intracarotid Amytal Procedure (IAP). The Intracarotid Amytal Procedure (IAP) is referred to by many different names, most commonly the Wada test, for the neurologist (Juhn Wada) who first developed the technique. The procedure is performed in the context of cerebral angiography, and involves the direct anesthetization of one cerebral hemisphere with sodium amobarbital. The transient period of anesthetization allows for direct examination of language capacity of the contralateral hemisphere. A brief memory examination was added to the procedure by Brenda Milner in order to predict patients who may be at risk for anterograde amnesia following unilateral temporal lobectomy. A minimally invasive technique, the IAP is considered essential in the consideration of patients for temporal lobectomy. The IAP has evolved over time to include more sophisticated assessments of expressive and receptive language, higher cognitive functioning, and lateralization of emotional responses. The study of memory functioning during the IAP is also a valuable predictor of response to temporal lobectomy. When the IAP and other, noninvasive neuropsychological test results are concordant with EEG and MRI findings, patients may be spared a more invasive and costly depth electrode or subdural grid study.
The more recent history of the IAP is somewhat controversial, with some practitioners questioning the ability of the technique to predict a low frequency occurrence such as the dense anterograde amnesia suffered by patient H.M. Neuropsychologists, who seem to prefer uniformity, have also criticized the procedure because of the tremendous heterogeneity in techniques. Nonetheless, the findings with respect to seizure lateralization and prediction of seizure control following surgery are remarkably robust despite the variability in technique.
Mapping cognitive function during cortical stimulation
Evaluating cognitive functioning during intraoperative cortical stimulation or during chronic subdural implants is a cooperative, multidisciplinary venture. Neuropsychologists must work closely with the surgeon, electrophysiologist, neuroradiologists, and others to produce a functional map of the patient's brain. Definition of cortical areas such as "Broca's area" is determined by function rather than anatomical landmarks. Patients with epilepsy often have anomalous representation of cognitive functions because the seizures precipitated reorganization. When a patient has language symptoms as part of ictal or post-ictal semiology, precise localization is needed to ensure protection of language function following a resection. Neuropsychological assessment of language during direct cortical stimulation allows the surgeon to precisely identify cortex which is crucial for aspects of language.
Validation of advanced technological methods
Advances in functional imaging hold promise for minimally or completely noninvasive in vivo correlation of anatomy and function. However, there are limitations to the techniques as they are presently available, and they require correlation with more established evaluation techniques prior to widespread acceptance.
Functional imaging with increasingly powerful MR techniques currently supplements more established procedures such as cortical mapping and the IAP. Localization of function via fMRI will greatly facilitate noninvasive evaluation of surgical candidates. However, while techniques such as fMRI may facilitate localization of regions that are activated during performance of cognitive functions such as naming, prediction of risk to function is still dependent upon deactivation paradigms such as cortical stimulation and IAP testing. Localizing techniques are also limited in their ability to provide important information about proficiency of function, which is obtained through more traditional clinical neuropsychological examination techniques. For example, fMRI may be able to demonstrate activation of the medial temporal lobe during word retrieval or other simple mnemonic tasks. However, prediction of a patient's functional status or performance level cannot be obtained from the fMRI data. Clinical examination of memory using a combination of verbal memory tests not only helps to localize to medial versus lateral temporal lobe, but allows prediction of the risk of decline for individual patients. This information is critical for counseling patients about anticipated outcome of temporal lobectomy, and for maximizing expected functional outcome.
Evaluation and intervention for enhanced psychosocial functioning
In the past, concepts of epilepsy treatment involved primarily the reduction of seizures. More widespread understanding of the impact of seizures on the whole person has led to a more integrated and comprehensive view of treatment. The inclusion of follow-up and "habilitation" programs for patients with seizures is a product of recognition of the impact of seizures on development and maintenance of a wide range of cognitive and psychosocial domains. These programs remain in the early development stage at most institutions. However, neuropsychologists, along with physicians, nurses, and other practitioners, are increasingly attuned to the needs of patients with respect to remediation of cognitive deficits, and acquisition of social and vocational skills.
Conclusions
Neuropsychology and epilepsy continue to have a reciprocal beneficial relationship. Advances in our understanding of cognitive and emotional function are fueled by detailed assessment of patients with epilepsy, which in turn enhances our ability to care for them. The integration of neuropsychology into comprehensive epilepsy care programs is a well established beginning. However, the challenge remains to improve the integration of care with patients' needs in the community and family.
References
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