Cortical excitability in drug naive juvenile myoclonic epilepsy

Abstract Purpose To evaluate the effect of diurnal variability on cortical excitability using single pulse transcranial magnetic stimulation (TMS), in drug naive patients with juvenile myoclonic epilepsy (JME) and to look for any differences in cortical excitability between males and females. Methods Thirty drug-naive patients with JME and 10 healthy controls were studied. Resting motor threshold (RMT), motor evoked potential (MEP), the duration of central motor conduction time (CMCT) and cortical silent period (CSP) were measured, twice, first early in the morning and again in the afternoon of the same day. Results Diurnal variation with higher evening values of CMCT and CSP were observed in the control group. In the study group, diurnal variation in RMT, CMCT and CSP was found with higher values in the morning than in control group. However, only the raised values of CSP [mean, 110.7ms, morning and 96.44ms, evening] were of statistical significance [ p =0.005, morning and 0.039, evening] as compared to controls. In the study group, males had higher values of RMT, CMCT and CSP than in females. However, the CMCT in males was lower in the evening study than in females. Further, RMT and morning CMCT was lower in females than in controls. In females, the morning CSP [mean, 100.91ms, morning versus 87.86ms, evening] was significantly prolonged [ p =0.017, morning versus 0.221, evening] as compared to controls. Conclusion The study is suggestive of the existence of impaired supraspinal/intracortical inhibitory circuits which may account for the hyperexcitability of the motor system being prominent in the morning among drug naive patients with JME. In this study, increased activity of cortical inhibitory networks, as evidenced by prolonged cortical silent period existed among drug naive JME patients, but was found to be significant only in female patients. This may explain the increased seizure susceptibility in this cohort, at this time of the day and an increased manifestation of JME in females.