The Related Factors to Atypical Language Dominance in Patients with Epileptic Foci in the Left Hemisphere

BACKGROUND: Several studies have revealed the increased incidence of atypical language dominance in patients with left hemisphere epileptic foci. We retrospectively investigated the incidence and related factors for language dominance shift determined by intracarotid amobarbital procedure (IAP) in patients with left hemispheric epilepsies. METHODS: We included 222 epileptic patients with epileptic foci in left hemisphere whose language dominance was determined by IAP at Asan Medical Center from 1994 to 2004. The items on the language test in IAP included spontaneous speech (6 items), understanding (2 items), and repetition (2 items). Language lateralization index (LI) was computed according to the formula L=(Score IAP right-Score IAP left)/(Score IAP right+Score IAP left). Clinical information was obtained from medical records including age, gender, age at onset of epilepsy, duration of epilepsy, frequency of seizures, risk factors, onset age of risk factors, and lateralization of MRI or EEG. RESULTS: Of the 222 patients (male 110 patients, 49.5%), complete left language dominance was 142 patients (64.0%), and complete right hemispheric language dominance was 29 patients (13.1%). Seizure onset age, onset age of risk factors, handedness and MRI lesions (hippocampal atrophy or left extensive lesion) had statistically significant association with atypical language dominance. On a linear regression analysis, the significant predictors of the atypical language dominancy were handedness and left extensive lesion (R2=.64). CONCLUSIONS: Atypical language dominancy in patients with left epileptic foci was highly correlated with non-right handedness and extensive lesion on the left hemisphere.

Influencing factors on interhemispheric language 'shift' and memory asymmetry in temporal lobe epilepsy

BACKGROUND AND OBJECTIVES: Interhemispheric memory asymmetry & language 'shift' (right hemisphere restitution of originally left hemisphere functions or vice versa) and its lateralizing value in temporal lobe epilepsy (TLE) have been repeatedly reported. We analyzed the factors influencing the memory asymmetry & language 'shift', which, to our knowledge, has rarely been reported. METHODS: The IAP (Intracarotid Amobarbital Procedure) was performed in 94 patients, who were candidates for temporal lobectomy. We determined language dominance (LD) hemisphere and calculated 'memory asymmetry indexes' (difference of percentage of memory recall between left and right hemisphere). We reviewed sex, history of 'risk factors' (episodes of febrile convulsion, head trauma, or meningoencephalitis during period of infant and early childhood), age of epilepsy-onset, duration of epilepsy, and then correlated each of them with the presence of language shift and the degree of memory asymmetry. RESULTS: Atypical LD (bilateral or right hemisphere LD) was significantly more frequent in left TLE group than in right (left TLE: 19%, right: 0%, p=0.009). The 'shift' of LD hemisphere was more frequent in patients with 'risk factors' (p=0.04). The 'shift' of LD hemisphere was seen only in patients with duration of epilepsy of > 10 years, but statistically not significant(p=0.07). Interhemispheric memory asymmetry occurred in most patients. The presence of 'risk factors' (p=0.05), duration of epilepsy of 10-20 years (p=0.04), and female sex (p=0.01) were significantly associated with the memory asymmetry in left TLE group. But in right TLE group, the memory asymmetry was not associated with above factors. CONCLUSION: Only in left TLE group, the presence of 'risk factors' and duration of epilepsy influenced both interhemispheric memory asymmetry & language 'shift', whereas sex influenced memory asymmetry only. In right TLE, we failed to find correlation. These results could be explained that in right TLE, memory might be easily or rapidly shifted to the contralateral hemisphere, even in absence of above factors.

Memory Functions of Temporal Lobe Epileptic Patients in the Intracarotid Amobarbital Procedure:I. Lateralizing Value

BACKGROUNDS: To examine the effects of seizure laterality and stimulus type on Wada memory performance in patients with temporal lobe epilepsy(TLE). METHODS: The subjects were 43 patients with medically intractable TLE (left TLE 26, Right TLE 17) who had no or rare seizures after surgery. The memory stimuli were concrete figures for some subjects and abstract figures for the other subjects. RESULTS: A clinical criterion of at least 2-points difference between left and right injections correctly classified 31(72%) patients into left and right TLE groups, with 4(9%) patients falsely classified. A discriminant function analysis(DFA) based on left and right injection scores allowed for a correct classification of 37(86%) patients into left and right TLE groups. When the memory stimuli were concrete figures, the correct classification rate was greater for right than left TLE patients. In contrast, with abstract figures, the correct classification rate was greater for left than right TLE patients. CONCLUSIONS: The Wada memory test is a valuable diagnostic aid in lateralizing temporal epileptogenic foci. Stimulus type as well as seizure lateralization is a major determinant of Wada memory asymmetries.