Ictal single photon emission computed tomography in absence seizures: Apparent implication of different neuronal mechanisms

Absence seizures represent a complex group of epilepsy, characterized by la pse of consciousness with staring. Bilateral, synchronous, and symmetric bu rsts of 3-Hz spike-and-wave discharges are observed on the electroencephalo gram, whereas interictal background activity is normal. This kind of epilep sy has to be differentiated from other generalized epilepsies such as juven ile absence epilepsy and juvenile myoclonic epilepsy. Moreover, absence sei zures, together with generalized spike-and-wave discharges, may coexist wit h other types of epilepsy such as frontal lobe epilepsy, temporal lobe epil epsy, benign epilepsy with centrotemporal spikes, and childhood epilepsy wi th occipital paroxysms. We have carried out ictal single photon emission co mputed tomography (SPELT) in 10 patients with clinical evidence of absence seizures with the aim to better understand and to distinguish this kind of seizure as primarily or secondarily generalized to a specific area and to o btain more information on the neuronal mechanisms involved in the different types of seizures, usually not identifiable at the first appearance. Durin g the long follow-up period (9 months to 14 years), 7 of the 10 examined pa tients underwent interictal SPELT when they became seizure free. Our data p ermitted, in two patients, the diagnosis of childhood absence seizures; in three patients, they suggested the possibility of later appearance of other seizure types, on the basis of focal hyperperfusion indicating a possible focal firing. In three of the examined patients, the diagnosis of idiopathi c localization-related epilepsies mimicking childhood absence seizures coul d be performed. In the last two patients, the hypothesis of a coexistence o f absences with partial and generalized seizures was considered. From our r esults, it can be presumed that ictal SPELT findings may contribute to the physiopathologic classification of the different types of epilepsies. Moreo ver, anticonvulsant treatment more appropriate to the different forms of se izures can be used.