SAN DIEGO—Supportive data for detecting epileptogenic zones in patients with temporal lobe epilepsy may be provided by positron emission tomography (PET), helping to reduce the need for invasive EEG studies, according to a study presented at the 130th Annual Meeting of the American Neurological Association.

"Our preliminary data suggest that PET imaging with a marker that shows deficits in signaling for the neurotransmitter serotonin is more sensitive than the traditional PET measurement of brain glucose," said William H. Theodore, MD, Chief of the Clinical Epilepsy Section at the National Institute of Neurological Disorders and Stroke.

"About 30% of patients with epilepsy, or approximately 600,000 people in the United States, have seizures that are not controlled by antiepileptic drugs. Surgery may be an option for some of these [patients], and localizing the epileptic focus is crucial," said Dr. Theodore.

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Serotonin 5-HT_1A receptor binding has been shown to be decreased in temporal lobe epilepsy. The investigators used PET to compare 5-HT_1A binding measured with the silent antagonist [¹⁸F]FCWAY to glucose metabolism measured with [¹⁸F]fluorodeoxyglucose (FDG) in 19 patients who had temporal lobectomy for uncontrolled epilepsy. The mean follow-up period was 31 months. Dr. Theodore’s research team analyzed PET data with coregistered MRI and partial volume correction, computing an asymmetry index for anatomic regions drawn on each patient’s coregistered MRI scan. Mean FDG asymmetry in the resected region was 0.25 versus 0.47 for FCWAY. Three patients—including one with normal MRI—had unrevealing FDG-PET but a clear FCWAY asymmetry. There was a trend for 13 patients who were seizure-free to have greater FCWAY asymmetry than FDG asymmetry, as compared with six patients with persistent seizures. "Our preliminary results suggest that FCWAY-PET may be more sensitive than FDG for presurgical evaluation of temporal lobe epilepsy," noted the investigators.

In their study, Dr. Theodore and colleagues found that a marker for serotonin systems was able to identify epileptogenic zones even in a patient with normal MRI. In related studies, the researchers found that deficits in serotonin correlate with the likelihood that patients with epilepsy will also have depression.

Dr. Theodore cautioned that the data are from a preliminary study of a procedure that is still in the research stages. However, he suggested that physicians should not hesitate to treat patients with epilepsy and depression with effective antidepressant drugs or to refer patients for surgical evaluation if seizures are not controlled by antiepileptic drugs.

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Suggested Reading
Giovacchini G, Toczek MT, Bonwetsch R, et al. 5-HT 1A receptors are reduced in temporal lobe epilepsy after partial-volume correction. J Nucl Med. 2005;46:1128-1135.
Theodore WH. Serotonin receptors: a new epilepsy imaging modality? Epilepsy Curr. 2005;5:33-34.

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