Ictal near infrared spectroscopy in temporal lobe epilepsy: a pilot study

Near infrared spectroscopy (NIRS) is a non-invasive method to measure cerebral tissue oxygenation continuously with an adhesive optode system which can be easily placed on the skin. We coupled NIRS with video-electroencephalography (video-EEG) during the presurgical evaluation of two patients with intractable localization-related epilepsy of mesial temporal origin. Cerebral oxygen saturation was measured either ipsilaterally (three seizures) or contralaterally (four seizures) to the primary epileptogenic zone. Since NIRS measures cerebral tissue oxygenation in a depth of only few centimetres, it did not record within the primary epileptogenic zone in our patients. Therefore we decided to place the NIRS optodes comfortably for the patients on the hairless skin corresponding with measurement of the oxygenation within the corresponding frontal cortex. Ipsilateral measurement revealed a marked desaturation in the course of the seizure with a postictal maximum whereas contralateral findings were inconsistent. The favourable outcome of selective amygdalahippocampectomy in both cases retrospectively confirmed the correct lateralization by video-EEG and the concordant NIRS findings. Our preliminary results suggest that NIRS might be a simple, cost-effective and non-invasive additional method to lateralize the primary epileptogenic zone in temporal lobe epilepsy and should be further investigated in larger series of patients.