Abstracts

Rationale: Epileptogenesis occurs during a latent period between a brain insult and onset of clinical seizures and may also extend into the initial period of clinical epilepsy. In rats, age-dependent angiogenesis, chronic brain inflammation, and excitotoxic damage associated with cerebral glucose hypermetabolism have been described during epileptogenesis. In children, Sturge-Weber syndrome (SWS) is a unique clinical model to study brain metabolic abnormalities during the presumed period of epileptogenesis, due to early diagnosis made possible by the facial port wine stain. Interictal focal glucose hypermetabolism on PET, unrelated to ongoing epileptic activity, was initially reported in two infants with SWS and recent seizure onset (Chugani et al., 1989). Subsequently, Pinton et al. (1997) reported focal hyperperfusion on SPECT in SWS infants who had not yet developed seizures. To better understand the significance of this metabolic phenomenon, we studied clinical correlates of interictal hypermetabolism in children with SWS who underwent FDG PET as part of a prospective, longitudinal study. Methods: Seventy interictal glucose PET scans performed with EEG monitoring in 36 children (age: 2 months-11 years, mean: 3.6 years) with unilateral SWS were reviewed for focal hypo- or hypermetabolism. Twenty-one patients had two or more consecutive PET scans with a mean follow-up time of 2.6 years. Seizure variables and clinical course as well as metabolic changes were analyzed in patients with and without hypermetabolism. Results: Focal cortical hypermetabolism, associated with no epileptiform activity on EEG, was seen in 8 patients (22%), including 2 infants whose first clinical seizures occurred after the first scan. Mean age and duration of epilepsy of these 8 patients were much lower than those of the other 28 patients with decreased focal glucose uptake (mean age: 1.5 vs. 4.3 years, respectively; p=0.006; mean duration: 7 months vs. 3.2 years; p=0.008). The incidence of increased metabolism was 41% (7/17) in children scanned before 2 years of age. Hypermetabolism never occurred in patients whose first scan showed hypometabolism, and increased metabolism was transient in all 5 patients who had repeated PET scans (follow-up: 7 months - 1.8 years) and switched to hypometabolism in four. Four of the 8 patients with increased metabolism developed uncontrolled seizures and underwent hemispherectomy. In the other 4, however, seizures eventually became relatively controlled by antiepileptic medication. Conclusions: Interictal focal glucose hypermetabolism, not due to ongoing epileptic activity, is common in young children with SWS and is seen only during a limited period before and shortly after the first clinical seizures. Focal hypermetabolism in these cases may reflect a transient increase of metabolic demand in cortex undergoing excitotoxic tissue damage. This period may indicate a critical time window when therapeutic interventions (including neuroprotective or antiepileptogenic treatment) could be most effective to prevent severe epilepsy and diminish long-term tissue damage.