Abstracts

Rationale: The cortical silent period (CSP) findings in patients with epilepsy are variable. A lengthened CSP was found in untreated patients with idiopathic generalized epilepsy (IGE). However, normal CSP was reported in patients after a first-ever generalized seizure, patients with progressive myoclonic epilepsy, juvenile myoclonic epilepsy, and cryptogenic partial epilepsy (PE). In this study, we used transcranial magnetic stimulation (TMS) to investigate the difference of cortical excitability between patients with IGE or PE and normal controls. Methods: we consecutively recruited 175 drug-na ve patients with epilepsy (IGE 55, PE 120, mean age 29.1 yrs) and 80 age- and sex- matched normal subjects with no drug history for CNS. Based on the seizure semiology, EEG, and brain MRI, epileptic focus was lateralized into right (N=65), or left hemisphere (N=55) in PE patients. We measured TMS parameters including resting motor threshold (RMT), motor evoked potential (MEP) amplitudes, cortical silent period (CSP), intracortical inhibition (ICI, interstimulus interval 2-5ms) and facilitation (ICF, interstimulus interval 10-20ms). The TMS parameters were measured during seizure free state more than 48 hours in patients. Results: In IGE patients, interhemispheric differences of CSP were not found in any stimulus intensity (P > 0.05). However, the mean CSP was longer in IGE patients compared with normal controls at all stimulus intensities (P < 0.05). In PE patients, TMS parameters were compared between 1) ipsilateral hemisphere to epileptic focus (IH) vs. contralateral one (CH), or 2) IH or CH vs. normal controls, and 3) IH or CH vs. IGE patients. The mean CSP was significantly shorter in IH than that in CH at 120% and 140% of RMT (p < 0.05). Mean CSP duration in CH was significantly longer at the stimulus intensities 120 - 150% of RMT and that in IH was longer only at 120% of RMT than that of normal controls (p=0.005). Between PE and IGE patients, there were no significant differences of CSP at any stimulus intensity. RMT, MEP amplitudes, ICI, and ICF were not different among IGE, PE, and normal control groups. Conclusions: These findings suggest that the CSP may have a lateralizing value in partial epilepsy by shorter CSP in the epileptic hemisphere. Prolonged CSP in epilepsy patients compared to normal subjects may indicate the abnormally increased interictal cortical inhibition in human epileptic brain.