Role of concordance between ictal-subtracted SPECT and PET in predicting long-term outcomes after epilepsy surgery.

OBJECTIVE

F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) and ictally subtracted single photon emission tomography (iSPECT) are important for localizing the epileptogenic focus. The following study analyzes the role of inter-concordance between FDG-PET and iSPECT in predicting long-term outcomes after epilepsy surgery.

METHODS

We prospectively evaluated (January 2003-January 2008) patients undergoing surgery for temporal or extratemporal drug refractory epilepsy (DRE) who had at least a 5 years follow up. Patients with MRI and video EEG (vEEG) concordance for the seizure focus underwent iSPECT and FDG-PET. Concordance of the iSPECT and FDG-PET with each other and with the substrate (defined by MRI and vEEG) for temporal and extra-temporal epilepsies was evaluated and correlated with outcomes.

RESULTS

One hundred twenty-three patients (74 males) were included in the study (mean age at time of surgery: 18.9±10.41 years). The mean age of onset of seizures was 9.87±8.37 years. The most common semiology was complex partial (45%). When both FDG-PET and iSPECT were concordant with each other, this translated into a (class I Engel at 5 years) outcome of 62% for extra-temporal epilepsies (provided they were also concordant with the lesion, as defined by MRI and vEEG). This percentage was significant (p<0.01) compared with all other situations (both FDG-PET/iSPECT not concordant to MRI/vEEG, only PET or iSPECT concordant with MRI/vEEG). This correlation was not found for the temporal epilepsies, where the MRI and vEEG were the most important prognostic parameters. In both temporal and extratemporal epilepsies the concordance of the iSPECT/FDG-PET with the MRI/vEEG correlated with a better 5-year outcome (temporal: 70% vs 25%; extra-temporal: 62% vs 33%; p<0.05).

SIGNIFICANCE

Concordance between non-invasive investigations iSPECT and FDG-PET is an important predictive factor for surgical outcomes in extra-temporal epilepsy.