The dopamine system in idiopathic generalized epilepsies: identification of syndrome-related changes

The present study tests the hypothesis that the dopamine system is altered in idiopathic generalized epilepsy (IGE), and that the pattern of possible changes differs between juvenile myoclonic epilepsy (JME) and epilepsy with tonic-clonic seizures only (GTCS). The dopamine (DA) system was investigated with PET and a DA transporter (DAT) ligand [(11)C]PE2I in 13 patients with JME, 13 with GTCS, and 12 healthy controls. The binding potential (BP) to DAT was quantified in the caudate, putamen, and midbrain. The possible impact on function was evaluated by correlating regional BP with test performance in a battery of neuropsychological tests. Both patient groups showed a reduced BP compared to controls, albeit in different locations. JME patients had a lower tracer binding than controls in the midbrain (0.8+/-0.1 vs. 1.0+/-0.2, p=0.019), whereas GTCS patients had reduced tracer binding in the putamen (5.9+/-1.6 vs. 7.1+/-1.2, p=0.023). While GTCS patients showed impaired performance in motor functions and on one test of executive function, JME patients performed poorly also in tests of working memory and several tests of executive function. Alterations in the DA system seem to exist in both GTCS and JME. However, the regional distribution of these changes differs between the two syndromes, as does their association with psychomotor and working memory performance. The present data suggest that the two forms of IGE have different neuronal substrates.