| Epilepsy is a group of common disorders characterized by recurrent seizures. In neural membranes, the crucial substrate of epileptogenesis is an altered balance between excitation and inhibition. In the epileptogenic region of localization-related epilepsies, this altered balance is a core factor in the transition from the interictal to the ictal state. These concepts are generally accepted, yet if tools for assessing the balance between neural excitation and inhibition in the patient remain unavailable, they must remain separate from clinical practice. In addition, a common clinical problem is how to evaluate pharmacologic effects of antiepileptic drugs (AEDs) in patients with epilepsy at the beginning of their treatment. Transcranial magnetic stimulation (TMS) is a new means by which hypotheses regarding cortical excitability in epilepsy can be explored in vivo in humans. TMS is a noninvasive, painless, quantitative means to measure the excitatory and inhibitory state of the human primary motor cortex. The one goal of this study were to assess the changes of cortical function in patients with localization-related epilepsy by TMS and expected them to have a differential excitability that would distinguish the epileptogenic area from the remainder of the cerebral tissue, the other goal is to study whether TMS can be used to evaluate the effects of AEDs early. Part one Evaluation of Cortical Function in Patients with Localization-related Epilepsy by Transcranial Magnetic Stimulation Objectives:To assess interictal brain excitability of patients with localization-related epilepsy by single-pulse transcranial magnetic stimulation (TMS) and evaluate its significance to pathophysiologic mechanism of epilepsies. Methods:We selected 110 patients including 89 with localization- related epilepsy and similar clinical features in whom we located the epileptogenic area reliably, and 20 age-and sex-matched healthy controls. Stimulating both motor cortices by single-pulse TMS, we determined the motor threshold (MT) to TMS, the duration of the cortical silent period (CSP), cortical latency, and central conduction time. Results: 1. Of the 110patients, cortical latency and central conduction time were normal, but MT (36±4)% were significantly lower than in the controls (48±8)% (P<0.01), and CSP (62±8)ms were significantly shorter than in the controls (93±11)ms (P<0.01). 2. When compared between each subgroup and control group, there are lower MT and shorter CSP in all subgroups. The CSP was shorter markedly in patients with a seizure focus in the motor cortex than in patients with seizure foci located elsewhere and in patients with generalized seizures. However, there are the longest CSP in patients with seizure foci located elsewhere among three subgroups (P<0.01).3. There were no statistically significant differences in TMS variables between bilateral hemispheres in 21 patients with generalized seizures or the healthy controls. However, in patients with a seizure focus in the motor cortex, the hemisphere with epileptogenic area had a significantly lower MT(36±8)% than the contralateral (46±9)%,and shorter CSP(52±8)ms than the contralateral (64±10)ms (P<0.01).The CSP of the latter was shortened than the controls. In patients with a seizure focus in the non-motor cortex, the side with epileptogenic area had a significantly lower MT(35±6)% than the contralateral (48±8)%,and shorter CSP (78±8)ms than the contralateral (102±10)ms , but the contralateral CSP was longer when comparing with controls (93±11)ms (P<0.01). 4. Of the 110 patients, 31 were untreated and 79 were taking one or more antiepileptic drugs. The untreated patients had a significantly lower MT(27±5)% than the treated patients(42±6)%,and shorter CSP (33±8)ms than the treated patients (76±10)ms (P<0.01). Conclusion: Single-pulse TMS provided a valuable electrophysiologic insight into the interictal excitatory state of the cortex in localization-related epilepsy. TMS studies in patients with a seizure focus in the motor cortex indicate increased cortica... |
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