San Diego -- Positron emission tomography (PET) brain scans of a brainchemical messenger system may prove sensitive enough to help plan brainsurgery for epilepsy, according to a study presented at the 130thannual meeting of the American Neurological Association in San Diego.
"Our preliminary data suggest that PET imaging with a marker thatshows deficits in signaling for the neurotransmitter serotonin is moresensitive than the traditional PET measurement of brain glucose," saidsenior author William H. Theodore MD, chief of the Clinical EpilepsySection at the National Institutes of Neurological Disorders andStroke.
When drugs fail to control epilepsy, brain surgery is often theonly remaining therapeutic option. However, identifying the correctspot for surgery has traditionally required a separate preliminary --and inherently risky -- surgical procedure.
Epilepsy is a chronic illness of the brain that is estimated toaffect almost one percent of the U.S. population. During an epilepticseizure, nerve cells in the brain fire electrical impulses much fasterthan normal, often leading to loss of consciousness.and convulsions
In a subset of cases, the seizures always begin the same,identifiable area of the brain, then spread to other areas. Surgery toremove the area where seizures start can be safe and effective.
"About 30% of patients with epilepsy, or approximately 600,000people in the U.S., have seizures that are not controlled byantiepileptic drugs. Surgery may be an option for some of these, andlocalizing the epileptic focus is crucial," said Theodore.
Both PET and magnetic resonance imaging (MRI) are underinvestigation as tools to guide neurosurgeons to areas of the brainwhere epileptic seizures originate.
Theodore and colleagues at NINDS have found, in their pilotstudy, that a marker for serotonin systems was able to identifyepilepsy-generating brain areas even in a patient with a normal MRI.
In related studies, the researchers have found that thesedeficits in serotonin correlate with the likelihood that patients withepilepsy will also suffer from depression.
Theodore cautions that this is a preliminary study of aprocedure that is still in the research stages. However, he suggeststhat physicians should not hesitate to treat patients with epilepsy anddepression with effective antidepressant drugs, and to refer patientsfor surgical evaluation if seizures are not controlled by antiepilepticdrugs.
Serotonin 1A receptor imaging and temporal lobectomy.
RobertBonwetsch, MD, Giampiero Giovacchini, MD, Richard Carson, PhD, PatriciaReeves-Tyer, Kathy Kelley, MA, Peter Herscovitch, MD and William HTheodore, MD. Bethesda, Maryland.
Positron emission tomography (PET) may provide supportive datafor detecting epileptogenic zones in patients with temporal lobeepilepsy (TLE), helping to reduce the need for invasive EEG studies.Serotonin (5HT) 1A receptor binding has been shown to be decreased inTLE. We used PET to compare 5HT-1A binding measured with the silentantagonist 18FCWAY, to glucose metabolism measured with 18FDG, in 19patients who had temporal lobectomy for uncontrolled epilepsy, and amean follow-up of 31 months. We analyzed PET data with co-registeredMRI and partial volume correction, computing an asymmetry index (AI)using the formula  x [ipsilateral contralateral]/[ipsilateral +contralateral] for anatomic regions drawn on each patient sco-registered MRI scan. Mean FDG asymmetry in the resected region was0.25 0.18, versus 0.47 0.20 for FCWAY (P<0.001). Three patients,including one with normal MRI, had unrevealing FDG PET but a clearFCWAY asymmetry. There was a trend for 13 patients who wereseizure-free to have greater FCWAY (p<0.08), but not FDG AI, than 6patients with persistent seizures. Our preliminary results suggest thatFCWAY PET may be more sensitive than FDG for presurgical evaluation oftemporal lobe epilepsy.
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