The potential of status epilepticus (SE) to cause permanent neurologic sequelae has long been recognized. One study indicated that SE was the most important predictor of poor performance on the WAIS and the Neuropsychological Battery for Epilepsy.55 Several studies from the early 1970s estimated the rate of cognitive impairment from SE to be as much as 25%.56–58 Among the risk factors for the development of cognitive and behavioral decline after an episode of SE are early age of onset,56 longer duration of SE,58,59 failure to treat with antiepileptic drugs,56,60,61 and symptomatic etiology.58,61
In a retrospective study of 98 patients with SE, Aminoff and Simon59 found that only 10 patients had permanent cognitive decline. Of these 10 patients, 6 had damage clearly related to SE, and 5 of the 6 had SE lasting 2 hours or longer.
In another study, 10 of 193 children with SE showed cognitive impairment after a follow-up of 1 to 2 years.61 Of these 10 children, however, 8 had other possible causes of cognitive decline such as symptomatic epilepsy or progressive encephalopathy.
Dodrill55 found that adults who experienced more than 100 episodes of generalized tonic- clonic seizures were more likely to show poorer intellectual, neuropsychological, psychosocial, and emotional function than those who had experienced fewer episodes. Patients who had experienced SE, however, showed the poorest overall function, independent of the number of generalized tonic-clonic seizures.
Nonconvulsive status epilepticus (NCSE) also was evaluated as a potential cause of cognitive decline. The impact of NCSE on cognitive function was traditionally considered minimal because it does not produce such adverse systemic consequences of convulsive SE as hyperthermia, acidosis, hyperkalemia, pulmonary compromise, or cardiovascular collapse.63 A review of the literature found no evidence of long-term cognitive changes induced by NCSE.64 In 20 consecutive patients, Cockerell et al.65 found no intellectual sequelae with complex partial SE in the absence of acute neurologic precipitants. Stores et al.66 found that 28 of 50 patients with NCSE demonstrated intellectual deterioration, but the likelihood that NCSE was the primary pathologic factor remains unknown, as the etiology of the epilepsy was not reported in each case. Krumholz et al.67 found nine patients with NCSE with persistent or permanent cognitive dysfunction or memory loss. However, the patients in this study were enrolled over a 10-year period from two academic medical centers, and so the overall prevalence of poor cognitive outcomes from NCSE was actually low.
The association of absence seizures with cognitive decline is not clear. In a study of 118 patients with epilepsy, Farwell et al.40 found that patients with all seizure types except those with classic absence seizures demonstrated subnormal intelligence. Bourgeois et al.23 found that the IQ of patients with absence seizures was higher than the mean of all patients with epilepsy. Dam68 recognized that although patients with absence seizures showed normal intelligence, they demonstrated impaired attention and poor social adaptation. Loiseau et al.69 found that one-third of patients with absence seizures had a social maladjustment.
Wirrell et al.70 compared a consecutive, population-based series of children, some of whom had absence epilepsy and others of whom had juvenile rheumatoid arthritis (JRA), diseases that share a similar incidence, high remission rate, and outpatient manageability. Five categories of outcome were measured: academic-personal, behavioral, employment-financial, family relations, and social-personal relations. At follow-up after 10 or more years, those with absence epilepsy had significantly greater difficulties than their JRA peers in the academic-personal and behavioral categories. The comparison with JRA controlled, in large part, for stigma and the effects of chronic medication and illness. These findings suggest that many of the academic and social problems among patients with absence seizures result from the biological effects of their epilepsy (the underlying pathophysiology and interictal epileptiform activity) and, possibly, its treatment. (See Is absence epilepsy benign?)
Comparison of partial and generalized seizures reveals more specific deficits associated with partial epilepsy.71 Although early onset of generalized seizures is associated with poorer outcome than is early onset of partial seizures, in one study, no significant difference between the neuropsychological functioning of these two groups was observed overall.35 Memory deficits are more frequent and severe with partial seizures than with primary generalized epilepsies, however.72,73 The cognitive effects of partial epilepsy differ based on lateralization and localization of the seizure focus, with left temporal, right temporal, and frontal lobe epilepsy each producing different phenomena.
Classically, left temporal lobe epilepsy (left TLE) causes verbal memory deficits, whereas right TLE causes visuospatial impairment.26,38,74,75 Hermann et al.,76 however, found that the overall effects of the laterality of TLE on hemisphere-dependent cognitive functions were the exception rather than the rule. Mesial TLE is associated with generalized cognitive impairment in several areas:76
Mesial TLE is not associated with deficits in tests of attention, concentration, or executive function.
Extratemporal foci cause a different set of long-term cognitive changes from those caused by temporal foci. Brier et al. found that extra–temporal-lobe epilepsy patients performed better than right TLE patients on nonverbal memory measures and better than left TLE patients on measures of verbal memory.
Long-term cognitive change resulting from frontal lobe epilepsy (FLE) involves impairment of executive behavior:77
Wieser78 found that psychopathology was more common in FLE than in TLE. Helmstaedter et al.77 compared 35 patients with TLE to 23 patients with FLE with respect to attention, speed, motor coordination, verbal and nonverbal fluency, concept formation, response inhibition, anticipatory behavior, and memory span. FLE was associated with significantly poorer results on almost all tests, fluency being the exception. No group differences were found with regard to the lateralization of the epileptic focus or the presence of cerebral lesions. Smith and Milner79 found that patients with right-sided FLE had a higher incidence of cognitive estimation error than did patients with left-sided FLE or TLE. Further, a correlation between error score in cognitive estimation and lesion size for the left FLE group was found.
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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