Can changes in cortical excitability distinguish progressive from juvenile myoclonic epilepsy?

Abstract

We used transcranial magnetic stimulation (TMS) to investigate whether there were any characteristic cortical excitability changes in progressive myoclonic epilepsy (PME) compared to juvenile myoclonic epilepsy (JME).Six patients with PME were studied. Motor threshold (MT) at rest and recovery curve analysis using paired-pulse stimulation at a number of interstimulus intervals (ISIs) was determined. Results were compared to those of 9 patients with chronic refractory JME and 10 with chronic well-controlled JME.PME showed a marked increase in cortical excitability at all the long ISIs (p < 0.01), compared to refractory JME (effect sizes ranging from 1.4 to 1.9) and well-controlled JME (effect sizes ranging from 2.0 to 2.4). Significant differences at the short ISIs 2-5 ms were seen only on comparison with the well-controlled group (p < 0.05, effect size 0.6, 0.7). There were no significant differences in MTs of PME compared to either JME groups.Our findings demonstrate specific differences in cortical excitability using TMS between PME and those with JME, particularly at long latencies in the paired-pulse paradigm, implicating a role for γ-aminobutyric acid (GABA)(B) -mediated networks.