Development of myoclonus in patients with partial epilepsy during treatment with vigabatrin: an electroencephalographic study.

In the context of a study of the effects of gamma-vinyl-GABA (GVG) on seizure occurrence and on EEG abnormalities we present three cases with focal epilepsy in which new clinical and EEG paroxysmal manifestations were observed during GVG therapy. At that time, whereas an amelioration or no change in patients' habitual seizures were observed, myoclonic jerks appeared with related changes in the EEG paroxysmal abnormalities, represented by generalized polyspike and wave complexes. An electroclinical correlation was recorded in one case. These data indicate that, although occurring rarely, it is possible to have epileptic myoclonus during GVG treatment. Mechanisms underlying these manifestations are difficult to explain. Probably a shift in the anti/proconvulsant GABAergic balance towards the latter may compromise the therapeutic effect of GVG.