Lovely Choudhury
(Senior Clinical Psychologist)
Neuropsychological evaluation is an essential part of the comprehensive investigation of patients who are candidates for surgical treatment of epilepsy. The decision as to whether a patient is an appropriate surgical candidate is based upon data gathered by a team of professionals. Some of the necessary information is anatomical, derived from neuroimaging; some is physiological (EEG); and some is based on clinical history and seizure pattern. The contribution of neuropsychology is unique in providing data about function through evaluation of a patient’s strengths and weaknesses on cognitive tests.
In patients with epilepsy, neuropsychological assessments are most frequently used to aid diagnosis, evaluate the cognitive side effects of antiepileptic medications and monitor the cognitive decline associated with some epileptic disorders.
In an ideal world, all newly diagnosed patients with epilepsy would undergo a brief neuropsychological screening prior to the onset of treatment. Whilst this may not provide significant additional diagnostic information at the time, it creates a valuable baseline against which future assessments can be measured.
The information obtained through traditional neuropsychological testing methods is used in several ways. Interpretation of the pattern of results on neuropsychological tests gives information about the site of epileptic focus, inferred from the pattern of cognitive dysfunction.
Comprehensive neuropsychological testing is indicated for most patients with intractable epilepsy. It is necessary to assess the cognitive, functional and motor abilities before surgery. Further, it is essential to counsel patients regarding the deficits that could develop following surgery based on the impact this would have on their quality of life. In conjunction with MRI and other pre-surgical investigations, neuropsychological scores are also used to assess the suitability of patients for epilepsy surgery and can be used to predict postoperative outcome both in terms of cognitive change and seizure control.
A typical neuropsychological evaluation will involve assessment of:
• General intellect
• Attention and concentration
• Language
• Visual–spatial skills
• Learning and memory
• Higher-level executive skills, such as problem-solving, reasoning, and shifting from one idea to another
• Motor abilities, and
• Mood and personality.
A basic battery includes measures of intelligence, fronto-executive skills, learning and memory (verbal, visual and behavioural memory tasks), attention, visuospatial abilities and language. Some sensory functions and motor skills are also tested. Such an arsenal of tests taps function in the frontal and temporal lobes. At its most fundamental level, the method underlying neuropsychological evaluation is to determine the dysfunctional hemisphere by comparing a patient’s performance on verbal tasks to performance on visuo-spatial or visuo-perceptual ones, and within the hemisphere to determine the dysfunctional region by comparing performance on various kinds of tasks. Results from this thorough, usually standardised, assortment of measures provide a reliable way of characterising and quantifying the nature and degree of cognitive dysfunction arising from epilepsy.
Neuropsychological assessment has an important role in evaluating candidates for temporal lobe surgery since the temporal lobes have long been implicated in memory functioning. Some patients who have been selected for epilepsy surgery also undergo pre- and postsurgical visual field and language examinations. The indication for these tests depends on the location and the extent of the surgery planned. Pre-surgical language function assessment is also performed when the presumed site is in the vicinity of the language area. The traditional view is that the dominant temporal lobe (usually the left) is important for verbal memory processing and the non-dominant temporal lobe (usually the right) for non-verbal or visual memory processing. However, within this model, the aetiology of the seizure disorder and the underlying pathology may play a critical role in shaping the nature and extent of pre- and postoperative neuropsychological deficits.
Given the general criteria for patient selection and the desired outcome of epilepsy surgery, it is possible to identify at least five specific areas in which neuropsychological evaluation has been used to enhance the delivery of services to these patients:
n Establishment of a baseline against which future comparisons can be made;
n Lateralisation and localisation of the seizure focus;
n Prediction of seizure control;
n Prediction of psychosocial outcome;
n Prediction of neuropsychological outcome.
The neuropsychological evaluation is an important part of the workup of an epileptic patient. These must be conducted and interpreted by a neuropsychologist who has specialised training in these procedures.