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

P>Purpose: 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). Methods: 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. Results: 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. Conclusion: 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 gamma-aminobutyric acid (GABA)(B)-mediated networks.