Long term effects of refractory temporal lobe epilepsy on cognitive abilities: a cross sectional study

Objective-Intractable epilepsy is related to various transient and chronic brain electric and neurochemical disturbances. There is increasing evidence that chronic epilepsy induces secondary neuronal metabolic and structural decline. However, there is no convincing evidence that the cognitive abilit ies of patients deteriorate with increasing duration of intractable epileps y. Methods-To examine whether duration of refractory temporal lobe epilepsy (T LE) is related to generalised cognitive impairment, psychometric intelligen ce based on the full scale intelligence quotient (FSIQ, WAIS-R) was determi ned in 209 patients with unilateral TLE. For analyses of variance (ANOVA) p atients were grouped into three categories: <15, 15-30, and >30 years of re fractory TLE. Results-An ANOVA and a multiple regression analysis showed that duration of TLE affects FSIQ. Patients with >30 years of TLE performed worse than pati ents with 15 or 30 years of TLE. The factors side of seizure origin and typ e of lesion an MRI did not reach significance. A second ANOVA including edu cation as factor showed that in patients with higher educational attainment , the mean FSIQ was stable for a longer duration of TLE than in less educat ed patients. Retesting 6 months after anterior temporal lobectomy seizure f ree patients (n=85 of 127) had an higher FSIQ but showed a similar duration effect before and after anterior temporal lobectomy. The variables age at epilepsy onset, education, frequency of interictal epileptiform discharges, frequency of habitual and generalised seizures, serum concentration of ant i-epileptic drugs, and polypharmacy were statistically controlled. Conclusions-Psychometric intelligence of patients with a longer duration of refractory TLE were most severely impaired. Consequently, refractory TLE s eems to be associated with slow but ongoing cognitive deterioration. It is assumed that epilepsy related noxious events and agents exhaust the compens atory capacity of brain functions. However, as in dementia and Alzheimer's disease, higher educational attainment as an indicator of higher brain rese rve might delay the cognitive decline.