Comparative study of cellular and synaptic abnormalities in brain tissue samples from pediatric tuberous sclerosis complex and cortical dysplasia type II.

Tuberous sclerosis complex (TSC) and severe cortical dysplasia (CD), or CD type II according to Palmini classification, share histopathologic similarities, specifically the presence of cytomegalic neurons and balloon cells. In this study we examined the morphologic and electrophysiologic properties of cells in cortical tissue samples from pediatric patients with TSC and CD type II who underwent surgery for pharmacoresistant epilepsy. Normal-appearing pyramidal neurons from TSC and CD type II cases had similar passive membrane properties. However, the frequency of excitatory postsynaptic currents (EPSCs) was higher in neurons from TSC compared to severe CD cases, particularly the frequency of medium- and large-amplitude synaptic events. In addition, EPSCs rise and decay times were slower in normal cells from TSC compared to severe CD cases. Balloon cells were found more frequently in TSC cases, whereas cytomegalic pyramidal neurons occurred more often in CD type II cases. Both cell types were similar morphologically and electrophysiologically in TSC and severe CD. These results suggest that even though the histopathology in TSC and severe CD is similar, there are subtle differences in spontaneous synaptic activity and topographic distribution of abnormal cells. These differences may contribute to variable mechanisms of epileptogenesis in patients with TSC compared with CD type II.