Abstracts

Rationale: The intracarotid amobarbital test (IAT) is the most widely used procedure for presurgical evaluation of language dominance in epileptic patients; however, it is highly invasive. Functional magnetic resonance imaging is an emerging noninvasive alternative, but it is more difficult in young children and in patients who cannot remain motionless during the procedure. The study aimed to determine whether near-infrared spectroscopy (NIRS) can be used as an alternative technique to investigate language dominance in epileptic children.Methods: The sample comprised 7 healthy right-handed children (age 5 13 years, 5 females, 2 males) and 10 epileptic patients (age 5 13 years, 5 females, 5 males). NIRS and handedness were assessed using the Edinburgh inventory and were performed on all 17 subjects. Four epileptic patients underwent IAT during their presurgical work-up. Informed consent was obtained from their parents and the project was approved by the Ethics Committees of NCNP. Twenty-four-channel NIRS machine (ETG-4000, Hitachi Medical Corp. Japan) was used. This device allows the use of 2 separate probe-containing shells, each with 5 semi-conductor laser light sources (780 and 830 nm), and 4 avalanche photodiode detectors arranged in an alternating fashion to form two 3 3 grids. The central probe in each temporal shell was positioned at the midpoint between the vertex and the external acoustic meatus. The word generation task was used and participants were instructed to name as many words as possible belonging to a familiar category (e.g., color, fruits) within 30 s. Subsequently, participants were asked to repeat the 5 pronounceable vowels (i.e., a, i, u, e, o) for 30 s. Each task was performed 5 times; data were averaged by blocks (5 for each task) and transformed to quantify oxyhemoglobin level changes in each channel. The NIRS laterality index (LI) was calculated using the following formula LI = (AL ? AR)/(AL + AR). AL and AR were calculated from the peak of oxyhemoglobin levels for the most activated channels over the 6 inferior frontal channels and that of mirror-imaged channels. The LI ranges from ?1 to 1; negative values (?1 to 0) indicate right language dominance and positive values (0 1) indicate left language dominance. Analysis involving the correlation between language dominance defined by NIRS, handedness, and IAT was performed.Results: NIRS was well tolerated; the patients remained cooperative and comfortable as their parents were beside them. The concordance rate with language dominance determined by NIRS and handedness was 86% in healthy children and 80% in the 10 epileptic children. Language dominance by NIRS and IAT was consistent in all 4 epileptic children. Conclusions: These data suggest that NIRS is a useful technique for pediatric and/or mentally retarded patients. NIRS is more effective because it is least impacted by patient s movement during the study and is comfortable to children. More studies using a larger sample size are needed.