Resting motor threshold (rMT) assessed by means of Transcranial Magnetic Stimulation (TMS) is thought to reflect trans-synaptic excitability of cortico-spinal neurons. TMS studies reporting rMT in idiopathic generalized epilepsies (IGEs) yielded discrepant results, so that it is difficult to draw a definitive conclusion on cortico-spinal excitability in IGEs by simple summation of previous results regarding this measure. Our purpose was to carry out a systematic review and a meta-analysis of studies evaluating rMT values obtained during single-pulse TMS in patients with IGEs. Controlled studies measuring rMT by single-pulse TMS in drug-naive patients older than 12 years affected by IGEs were systematically reviewed. rMT values were assessed calculating mean difference and odds ratio with 95\% confidence intervals (CI). Fourteen trials (265 epileptic patients and 424 controls) were included. Patients with juvenile myoclonic epilepsy (JME) have a statistically significant lower rMT compared with controls (mean difference: -6.78; 95\% CI -10.55 to -3.00); when considering all subtypes of IGEs and IGEs other than JME no statistically significant differences were found. Overall considered, the results are indicative of a cortico-spinal hyper-excitability in JME, providing not enough evidence for motor hyper-excitability in other subtypes of IGE. The considerable variability across studies probably reflects the presence of relevant clinical and methodological heterogeneity, and higher temporal variability among rMT measurements over time, related to unstable cortical excitability in these patients.
