Neuroimaging evidence of progressive neuronal loss and dysfunction in temporal lobe epilepsy

Whether temporal lobe epilepsy is the result of an isolated, early injury o r whether there is ongoing neuronal dysfunction or loss due to seizures is often debated. We attempt to address this issue by using magnetic resonance techniques. Proton magnetic resonance spectroscopic imaging can detect and quantify focal neuronal dysfunction or loss based on reduced signals from the neuronal marker N-acetylaspartate (NAA), and magnetic resonance imaging (MRT)-based measurements of hippocampal volumes (MRIvol) can quantify the amount of atrophy in this Structure. We performed magnetic resonance spectr oscopic imaging and MRIvol in 82 consecutive patients with medically intrac table temporal lobe epilepsy to determine whether there was a correlation b etween seizure frequency, or type or duration of epilepsy, with NAA to crea tine (Cr) values or hippocampal volumes. Volumes and spectroscopic resonanc e intensities were categorized as to whether they were measured from the te mporal lobe ipsilateral or contralateral to the predominant electroencephal ographic focus. Ipsilateral and contralateral NAA/Cr was;negatively correla ted with duration of epilepsy. Hippocampal volumes were negatively correlat ed with duration ipsilaterally but not contralaterally. Frequency of comple x partial seizures was not correlated with any of the magnetic resonance me asures. However, patients with frequent generalized tonic-clonic seizures h ad lower NAA/Cr bilaterally and smaller hippocampal volumes ipsilaterally t han patients with none or rare generalized tonic-clonic seizures. The resul ts suggest that although an early, fixed injury may cause asymmetric tempor al lobe damage, generalized seizures may also cause progressive neuronal dy sfunction or loss.