Abstracts

Rationale: Photosensitivity (PS) is reported to occur in approximately 30% of patients with juvenile myoclonic epilepsy (JME). This specific reflex epileptic mechanism may be related to activation of circumscribed cortical areas of functional anatomic systems that, due to some functional instability, probably genetically determined, respond with epileptic discharges. This hypothesis was recently demonstrated in photosensitive baboons (Papio hamadryas spp) with PET imaging. Understanding the interaction between these functional circuits may shed light on the pathophysiology of PS and JME. The purpose of this study was to investigate the cerebral metabolic differences between patients with JME with and without PS.Methods: All patients had a typical history of JME, typical prolonged video-EEG findings and normal high-resolution magnetic resonance neuroimaging (MRI). None of them had other neuropsychiatric disease. PS was defined as generalized spikes, spike- or polyspike-wave paroxysms occurring at least twice during intermittent photic stimulation. Sixty JME patients with a median age of 26 (range 14-55) years, 19 (32%) of whom were photosensitive, were submitted to 1.5 T MRI proton spectroscopy (1H-MRS) study. Multi-voxel 1H-MRS was acquired using PRESS sequence (TR/TE = 1500/30 ms) over the following locations: medial prefrontal cortex, primary motor area, thalamus, striatum, posterior cingulate gyrus, insula and occipital cortex. We determined ratios for integral values of N-acetyl aspartate (NAA), choline (Cho), glutamine-glutamate (GLX) and myo-inositol (Ins) over creatine-phosphocreatine (Cr). The control group (CTL) consisted of 30 unmedicated, age and sex-matched healthy volunteers. The Ethics Committee approved the study and informed consent was obtained from all participants.Results: Patients with JME with (JME-PS) and without (JME-NPS) PS did not differ regarding age, duration of disease, treatment and seizure control. Group analysis demonstrated a significant reduction of NAA/Cr in the thalamus of JME-PS patients compared to the JME-NPS and CTL groups (1.9 vs. 2.8 vs. 3.3; p = 0.01) and in primary motor area (2.1 vs. 2.2 vs. 2.4; p = 0.02). Also, GLX/Cr ratio was significantly increased in the thalamus of JME-PS compared to JME-NPS and CTL (0.6 vs. 0.5 vs. 0.3; p = 0.006), but it was significantly decreased in the medial prefrontal cortex (0.4 vs. 0.5 vs. 0.6; p = 0.02) and primary motor area (0.5 vs. 0.4 vs. 0.6; p = 0.03).Conclusions: This study supports the view that the thalamo-cortical circuitry seems to be associated with PS in JME. A striking finding was the absence of occipital involvement in these patients. Reductions in NAA may represent either loss or injury of neurons and/or axons, as well as metabolic dysfunction while glutamate is considered to be an excitatory neurotransmitter in the brain which is involved in the pathogenesis of seizures. However, whether altered GLX directly represents increased or decreased glutamatergic neurotransmission is not yet established.