Abstracts

Rationale: Approximately 80% of patients with tuberous sclerosis complex (TSC) develop epilepsy, although the mechanisms of epileptogenesis are unclear (NEJM, 2006;355:1345-56). Cortical tubers are present in over 80% of patients with TSC and are pathologically characterized by areas of disrupted cortical architecture attributed to abnormal cellular migration during fetal corticogenesis. Some tubers, but not others, appear to serve as epileptogenic foci. Tubers can exhibit cyst-like changes over time (Epilepsia, in press) and the presence of a cyst-like tuber has been shown to correlate with a more severe epilepsy history (Neurology, 2009;72:1165-9). It is unknown whether cyst-like tubers have altered physiological characteristics or whether they are independent features seen in more malignant disease. The purpose of this study was to evaluate whether the gross location of cyst-like tubers on MRI registers anatomically with the gross location of epileptiform activity on scalp EEG. Methods: We performed a retrospective chart review of all patients with definite clinical TSC followed at our institution. Patients with at least one cyst-like tuber present on MRI and EEG recordings within one year of neuroimaging available for review were included. For both EEG and MRI analyses, the cerebrum was divided into quadrants (left-anterior, right-anterior, left-posterior, and right-posterior). For MRI analysis, the plane containing the central fissure defined the left-right boundary and the plane containing the central sulcus defined the anterior-posterior boundary. Each brain quadrant was evaluated for the number of cyst-like tubers present within it. For EEG analysis, the anterior quadrants included the F, Fp, and C electrodes and the anterior temporal electrodes T3 and T4. The posterior quadrants included the P and O electrodes and the posterior temporal electrodes T5 and T6. EEGs were analyzed for interictal epileptiform activity by quadrants by a neurophysiologist blinded to MRI data. When an epileptiform discharge appeared to lie on a midline (z) electrode, laterality was assigned to the quadrant where the discharge was of highest amplitude. Spikes and sharp waves were counted and averaged to a value per minute and each quadrant was assigned a semi-quantitative score ranging from 0 to 6. Statistical analyses were performed using chi-square analyses and linear logistic regression. All reported p values used two-tailed tests of significance with α set at 0.05. Results: 40 patients were included, resulting in 160 brain quadrants for analysis. The presence of a cyst-like tuber in a quadrant correlated with epileptiform activity in the same quadrant (p = 0.049). There was no relationship between the number of cyst-like tubers present and the severity of EEG abnormalities in the same quadrant (linear logistic regression, p=0.5). Conclusions: Cyst-like cortical tubers co-register with epileptiform activity on EEG and may contribute to the more severe epilepsy profile seen in TSC patients with these lesions.