Epileptic Disorders
MENUThe effect of valproate on silent period and corticomotor excitability Volume 8, issue 2, June 2006
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- Key words: valproate, corticomotor threshold, silent period, transcranial magnetic stimulation
- Page(s) : 136-42
- Published in: 2006
Objective. To investigate, by transcranial magnetic stimulation, the effects of valproate on silent period and corticomotor excitability. Methods: thirty patients with generalized epilepsy were studied at baseline, and re-examined 4 (S1) and 25 (S2) weeks after the administration of valproate (mean dose: 1040 ± 284 mg). Transcranial magnetic stimulation was performed with a figure of eight coil (recording, first dorsal interosseous). Threshold was measured at 1% steps. Silent period was measured using a recently described protocol. Briefly, silent periods were elicited at 5% increments from 0 to 100% maximum stimulus intensity. At each stimulus intensity, 4 silent periods were obtained and the average value of silent period duration was used to construct a stimulus/response curve of stimulus intensity versus silent period. The resulting curves were then fitted to a Boltzman function and were statistically compared. The motor-evoked potential recruitment curve was constructed under active conditions and analyzed in a similar way. Results. Valproate increased threshold from 36.5 ± 5.99% at baseline to 41.02 ± 7.84% at S1 (p < 0.0001, paired t-test). The maximum value of the silent period curve decreased from 257.5 ± 3.9 ms at baseline to 230.3 ± 3.9 ms at S1 (p < 0.0001, F-test and AIC) while the other best-fit values (V 50, slope, threshold) were not significantly affected. Regarding the motor-evoked potential recruitment curve, the maximum value decreased significantly post-drug (from 0.449 ± 0.007 to 0.392 ± 0.009, p < 0.01, F-test and AIC test), whereas the rest of the best-fit values remained unaffected. Conclusion. In patients with idiopathic generalized epilepsy, valproate increases threshold and reduces the maximum values of the silent period curve and the motor-evoked potential recruitment curve. These findings probably reflect valproate’s effects on voltage-dependent Na + channels, as well as an activation of GABA A receptors.