Prognostic contribution of subtraction between ictal and interictal SPECT and its alignment to MRI (SISCOM) in patients with pharmacorresistant epilepsy associated to normal 3T MRI

Presurgical evaluation aims to localize the presumed epileptogenic zone (PEZ) through a multidisciplinary evaluation that includes: ambulatory electroencephalogram (EEG), Video-EEG, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), ictal and interictal SPECTs, PET (positron emission tomography) and neuropsychological evaluation. The MRI is the structural neuroimaging of choice for investigation of potentially epileptogenic lesions. The problem arises when a high-field MRI is unable to reveal abnormalities (i.e. negative MRI). In these cases, SISCOM has been used to review an MRI and for implantation of invasive electrodes. The objectives of this project were: (a) To evaluate the contribution of SISCOM in the presurgical and therapeutic evaluation of patients with negative-3T MRI; b) To evaluate the neurovascular coupling (NVC) through the interictal SPECT and PET; This study assessed the agreement between SISCOM and video-EEG in 40 patients with refractory epilepsy and negative-3T MRI. To assess blood-input and abnormal neuronal metabolism to the negative-MRI, we investigated neurovascular coupling (NVC) in a subgroup of 32 patients who performed brain PET. Patients were intravenously administered with 1,480MBq of 99mTc-ECD for ictal/interictal SPECT. The brain PET was acquired with 185 MBq of activity. The SPECTs and the PET were aligned using a multiplanar T1-weighted MRI. SISCOM findings were correlated with video-EEG and other pre/post-surgical evaluation data. SISCOM was the technique with the highest agreement rates with video-EEG (81%), followed by ictal SPECT (56%). The area of invasive approach proposed by the team from the clinical meeting was more restricted in 75% of cases in which SISCOM was concordant with the video-EEG. Among those patients with good surgical results, the SISCOM focus was completely resected in 50% of the patients. Among those patients with poor surgical outcome, the SISCOM focus was not resected in 75% of the patients. Analysis of PET and interictal SPECT showed changes in the coupling between blood supply and neuronal metabolism in the interictal period. We concluded that SISCOM contributed to the diagnostic hypothesis of EZ with a more topographically selective investigation through invasive-EEG. The pathophysiological study of refractory epilepsy with negative-3T MRI revealed changes in perfusion and metabolic coupling in the interictal period. (AU)