MAGNETIC STIMULATION OF THE BRAIN IN GENERALIZED EPILEPSY - REVERSAL OF CORTICAL HYPEREXCITABILITY BY ANTICONVULSANTS

Observations on experimental models suggest that diffuse cortical hype rexcitability is an important abnormality in the generalized epilepsie s. We used the threshold for transcranial magnetic stimulation as an i ndex of motor cortical excitability in 89 neurologically normal contro l subjects and 56 patients with idiopathic generalized epilepsy (20 un treated and 36 chronically treated with anticonvulsants). Magnetic sti mulation was repeated in 10 patients after valproate monotherapy had b een commenced and in 23 control subjects. The threshold intensity was significantly lower in the untreated patients (46 +/- 5% [mean +/- 95% confidence interval]) than in the control subjects (56 +/- 2%). Treat ed patients had significantly higher thresholds (64 +/- 4%) than did u ntreated patients and control subjects. A significant increase in thre shold intensity (8 +/- 2%) occurred in patients retested after startin g valproate; there was no significant change in retested control subje cts (- 1 +/- 2%). Threshold intensity was positively correlated with p lasma valproate levels (r(s) = 0.37). The findings suggest that cortic al excitability is increased in idiopathic generalized epilepsy and is reduced following anticonvulsant treatment. Transcranial magnetic sti mulation is of use in examining the pathophysiology of generalized epi lepsy. Furthermore, changes in threshold intensity in response to anti convulsant treatment may prove useful in guiding therapy.