Pathophysiology of Tonic Muscle Activation During Epileptic Seizures: Abstract of paper SC223

Tonic seizures and the tonic phase of tonic-clonic epileptic seizures are defined as a “sustained tonic” muscle contraction. Visual inspection of the surface electromyograms (sEMG) during seizures significantly contributed to a better understanding and diagnosis of several seizure types. However, quantitative analysis of the sEMG during the epileptic seizures has received surprisingly little attention.

The aim of our study was to elucidate the pathophysiology of the tonic muscle activation during seizures. SEMG was recorded from the deltoid muscles, during 58 seizures from 18 patients (9 with generalised tonic and 9 with tonic-clonic seizures). 18 age and gender matched normal controls simulated 90 generalised tonic seizures.

We calculated the root mean square (RMS) of the amplitudes, the median frequency (MF), the relative power (RP) and the coherence. During the epileptic seizures (especially the tonic ones) there was a significant shift towards higher frequencies, expressed by increase in the MF and RP 100-500Hz. The amplitude characteristic (RMS) was significantly higher during the tonic phase of the tonicclonic seizures as compared to the simulated ones, while the RMS of the tonic seizures was significantly lower than the simulated ones.

The coherence was significantly higher during the epileptic seizures. The mechanism of muscle activation during epileptic seizures is different from the physiological one. Furthermore the sustained muscle activation during the tonic phase of tonic-clonic seizures is different from that during tonic seizures suggesting that distinct efferent neural pathways are involved in the generation of the sustained muscle contraction during tonic and tonic-clonic seizures.