Spectrum of motor responses elicited by electrical stimulation of primary motor cortex: A polygraphic study in patients with epilepsy

OBJECTIVE

To study the neurophysiology of motor responses elicited by electrical stimulation of the primary motor cortex.

METHODS

We studied motor responses in four patients undergoing invasive epilepsy monitoring and functional cortical mapping via electrical cortical stimulation using surface EMG electrodes. In addition, polygraphic analysis of intracranial EEG and EMG during bilateral tonic-clonic seizures, induced by cortical stimulation, was performed in two patients.

RESULTS

(a) Electrical cortical stimulation: The motor responses were classified as clonic, jittery, and tonic. The clonic responses were characterized by synchronous EMG bursts of agonist and antagonistic muscles, alternating with silent periods. At stimulation frequencies of <20 Hz, EMG bursts were of ≤50 ms duration (Type I clonic). At stimulation frequencies of 20-50 Hz, EMG bursts were of >50 ms duration and had a complex morphology (Type II clonic). Increasing the current intensity at a constant frequency converted clonic responses into jittery and tonic contractions. (b) Bilateral tonic-clonic seizures: The intracranial EEG showed continuous fast spiking activity during the tonic phase along with interference pattern on surface EMG. The clonic phase was characterized by a polyspike-and-slow wave pattern. The polyspikes were time-locked with the synchronous EMG bursts of agonists and antagonists and the slow waves were time-locked with silent periods.

INTERPRETATION

These results suggest that epileptic activity involving the primary motor cortex can produce a continuum of motor responses ranging from type I clonic, type II clonic, and tonic responses to bilateral tonic-clonic seizures. This continuum is related to the frequency and intensity of the epileptiform discharges with tonic seizures representing the highest end of the spectrum.

Cortical Excitability in Temporal Lobe Epilepsy with Bilateral Tonic-Clonic Seizures

OBJECTIVE

We investigated motor cortical excitability (CE) in unilateral temporal lobe epilepsy (TLE) and its relationship to bilateral tonic-clonic seizure (BTCS) using paired-pulse transcranial magnetic stimulation (TMS).

METHODS

In this cross-sectional study, we enrolled 46 unilateral TLE patients and 16 age-and sex-matched healthy controls. Resting motor thresholds (RMT); short-interval intracortical inhibition (SICI, GABAA receptor-mediated); facilitation (ICF, glutamatergic-mediated) with interstimulus intervals (ISIs) of 2, 5, 10, and 15 ms; and long-interval intracortical inhibition (LICI, GABAB receptor-mediated) with ISIs of 200-400 ms were measured via paired-pulse TMS. Comparisons were made between controls and patients with TLE, and then among the TLE subgroups (no BTCS, infrequent BTCS and frequent BTCS subgroup).

RESULTS

Compared with controls, TLE patients had higher RMT, lower SICI and higher LICI in both hemispheres, and higher ICF in the ipsilateral hemisphere. In patients with frequent BTCS, cortical hyperexcitability in the ipsilateral hemisphere was found in a parameter-dependent manner (SICI decreased at a stimulation interval of 5 ms, and ICF increased at a stimulation interval of 15 ms) compared with patients with infrequent or no BTCS.

CONCLUSIONS

Our results demonstrate that motor cortical hyper-excitability in the ipsilateral hemisphere underlies the epileptogenic network of patients with active BTCS, which is more extensive than those with infrequent or no BTCS.

[New classification of epileptic seizures : A critical evaluation of the changes]

In the new classification of epileptic seizures by the International League Against Epilepsy (ILAE), a multitude of changes are recommended particularly for seizures of focal origin. In addition to aspects of the nomenclature, this involves the introduction of different levels of classification with respect to the state of consciousness and the evolution to a bilateral tonic-clonic seizure, the inclusion of the first semiological seizure element in the classification and a new operationalization of the state of consciousness. This leads partly to specification in the description but in some areas also to counterintuitive changes in the classification. The advantages and disadvantages of this reorganization for the clinical practice are critically discussed with reference to the most important modifications.