Abstracts

RATIONALE: MCD are present in up to 15% of adult patients with medically refractory epilepsy referred for epilepsy surgery. Surgery in these patients has a less favourable outcome than if there is a discrete lesion, probably due to the presence of abnormalities beyond those appreciated on standard MRI. [¹¹C]DPN PET images all subtypes of opioid receptors. There is evidence that release of endogenous opioids accompanies partial seizures.
METHODS: We studied 14 patients with partial epilepsy due to MCD. Four had subcortical forms of MCD: 2 band heterotopia (BH), 1 subependymal nodular heterotopia (SNH) and one subcortical heterotopia (SH). Ten had cortical or mixed forms: 3 focal cortical dysplasias (FCD), 2 dysembryoplastic neuroepithelial tumours (DNT), 1 schizencephaly (Schiz), 1 perisylvian polymicrogyria (PMG) and 3 tuberous scleroses (TS). 20 healthy controls were studied for comparison. All had high resolution MRI and quantitative [¹¹C]-DPN PET. Spectral analysis was used to produce parametric images of DPN volume-of-distribution (Vd). SPM99 with explicit masking was used for the comparison of individual patients and controls.
RESULTS: 13 of the 14 patients showed abnormal DPN-Vd. Two patients had increases of DPN-Vd, five had decreaes and six both increases and decreases. Within subgroups, findings tended to be similar. The two BHT patients showed increases in the band itself with widespread cortical decreases. Similarly, the heterotopia in the patients with SNH and SH were detected as increases compared with the homologous regions in controls, but both had significant decreases of DPN-Vd in the vicinity of the single lesion. The patient with Schiz had increases within the thickened cortex in the clefts but decreases in the surrounding areas. Of the three patients with FCD, only one had a decrease within the lesion; there were no increases, one normal study and one patient with remote decreases. Both patients with DNT showed increases in the lesion and contralaterally. The patient with PMG had widespread increases and decreases. The three patients with TS had no increases, and decreases were confined to some of the cortical tubers.
CONCLUSIONS: [¹¹C]DPN PET showed abnormalities in 13/14 MCD patients. Subtypes of MCD seem to have characteristic appearances. In some forms, abnormalities are confined to the lesions seen on MRI, but particularly the subcortical forms show more widespread disturbances, in accordance with their lesser suitability for epilepsy surgery. Quantitative region-based analyses with correction for tissue type will determine whether there is functional abnormality over and above structural abnormalities.
Support: Deutsche Forschungsgemeinschaft (HA 3013-1), Action Research, the Medical Research Council and the National Society for Epilepsy