We evaluated the role of positron emission tomography (PET) with [18F]deoxyglucose (FDG) (FDG-PET) for planning surgery in 53 patients who had temporal lobectomy for uncontrolled seizures at National Institutes of Health from 1981 to 1990. Investigators blinded to PET data used results of telemetered video-electroencephalographic ictal monitoring and other standard criteria to decide whether subdural electrodes (22 patients, i.e., the "invasive" group) should be implanted or surgery performed. PET scans were analyzed using a standard regional template. Mean lateral but not mesial temporal asymmetry was significantly higher in patients who became seizure free (p < 0.03). Patients with > or = 15% hypometabolism were significantly more likely to be seizure free in the entire study population and the invasive subgroup. Visual identification of hypometabolism was less accurate. When a clear temporal ictal surface electroencephalographic focus was present, FDG-PET provided less additional information. FDG-PET may be particularly valuable if the surface electroencephalographic scan is nonlocalizing. In addition to helping to identify the seizure focus, it may allow limitation of invasive electrode placement to those necessary for functional mapping. When PET is used to identify epileptic foci, quantitative measurements of asymmetry should be made.

No abstract

We examined the seizure records of 13 patients (nine men and four women, ages 27-50 years) with intractable partial epilepsy, maintained with steady anti-epileptic drug dosages. Patients recorded daily seizure frequency on calendars. Periods of outpatient observation ranged from 99 to 1,710 days and the number of observed seizures ranged from 18 to over 400, with daily seizure rates of 0.1-4.3 per day. We used the quasi-likelihood regression model to examine the following four departures of the daily seizure counts from a Poisson (random) model: (1) linear increasing or decreasing time trends in expected seizure rates; (2) clustering, where the expected seizure rate on a given day depends on the number of seizures observed on the immediate prior days; (3) monthly cyclicity; and (4) increased variability (overdispersion). Linear time trends were seen in six patients (four increasing and two decreasing), clustering was seen in 10 patients, and a near-monthly cycle appeared in four patients (two of nine men and two of four women). A significant amount of extra variation (overdispersion) relative to a Poisson distribution was observed in all but one of the 13 patients. Departures from a Poisson (random) model appear more common in this population of patients with medically intractable epilepsy than is commonly recognized, and have clinical importance as well as implications for the design of clinical studies.

We studied the effects of valproate (VPA) on local cerebral glucose metabolism (LCMRglc) in eight patients with partial seizure disorders and two with primary generalized epilepsy. Each patient had two positron-emission tomography (PET) scans with 18F-2-deoxyglucose (FDG), with, and without, VPA (mean level 52 mg/dl, range 30-127 mg/dl). Patients continued carbamazepine (CBZ) for both scans: serum concentrations were not significantly changed by VPA (CBZ range 5.4-12 mg/dl). Seven patients had the "without-VPA" scan first. Mean interval between PET scans was 75 days. Global CMRglc was decreased by 22% by addition of VPA (7.2 +/- 1.8 mg/100 g/min without VPA, 5.6 +/- 1.1 g/min with VPA, p less than 0.05, corrected). Thirteen regions of interest (ROIs) were analyzed in each hemisphere in each PET scan. Metabolic rates were significantly lower in 15 of 26 ROIs with VPA (p less than 0.05, corrected). VPA depresses cerebral metabolism to a greater degree than do CBZ and phenytoin (PHT) but less than does phenobarbital (PB). The metabolic effect may be related to the mechanism of action and have neuropsychological implications.