Abstracts

Rationale: Algorithms for timely diagnosis of a first seizure (FS) require a comprehensive clinical history, standard diagnostic testing with computerized tomography (CT), subsequent MRI imaging, routine electroencephalography (EEG) and sleep-deprived EEG. MRI and EEG are widely accepted as gold standards in investigation of all stages of epilepsy including FS presentations. Currently, we do not know the exact correlation between pathological findings on MRI and those identified on EEG. Methods: We retrospectively collected the MRI imaging and EEG data on 172 adult patients with confirmed seizures seen from May, 2008 to August, 2011 at the Adult First Seizure Clinic at the QE II Health Sciences Center, Dalhousie University (Halifax, Nova Scotia, Canada). The patients that had a confirmed seizure were given a diagnosis category of First Seizure (FS), if the index seizure was their only seizure. Alternatively, the patients were classed as New Onset Epilepsy (NOE) if the patient had had more than one seizure in the past 12 months; or Newly Diagnosed Epilepsy (NDE) if the patient had more than one seizure in a greater than 12 month time frame. EEG recordings were performed on a Stellate Harmony digital EEG system. MRI imaging was performed according to a specialized epilepsy protocol on a 1.5T GE Scanner. Results: 51% (87 of 172) of patients were FS, NOE was diagnosed in 41% (71 of 172), and NDE in 8% (14 of 172). We focused on patients who had undergone both an EEG and MRI (142 of 172). Almost a third (32%) of the patients presented with MRI findings which we considered clinically relevant (46 of 142). Similarly, 33% of the patients had abnormal EEG findings (47 of 142), out of which 15 were found to have generalized epileptiform discharges (GED). Interestingly, only 36% of patients with abnormal EEG findings also had an abnormal MRI (64% had a normal MRI), conversely 39% of the MRI positive patients had abnormal EEG findings (61% had a normal EEG). Only 12% of all patients showed pathologies on both modalities, MRI and EEG. 4 out of the 15 patients with GED had a pathological MRI. Statistical analysis over the whole group of this data (2x2 contingency table) showed that MRI findings and EEG findings were not linked (P=0.497). Conclusions: Our results suggest that MRI and EEG gave a similar percentage of diagnostic yield in identification of underlying morphological or functional pathology in patients presenting with FS, NOE or NDE. The significant lack of association between an abnormal EEG finding and an abnormal MRI finding suggested that they reflect complementary, but different aspects of pathologies in these subgroup of seizure patients. Thus, from a clinical practice perspective, both tests have to be performed to capture the full range of pathologies.