Increased population of oligodendroglia-like cells in pediatric intractable epilepsy

Pediatric focal epilepsies often involve more extratemporal regions than adult epilepsies. This study aims to investigate the population of oligodendroglia-like cells (OLCs) in the pediatric focal epilepsy patients requiring surgery. We hypothesize that OLCs are one of the factors that extend the pediatric epileptic network in intractable epilepsy. Thirty (18 female) patients (1.8-16.9 years old with a mean of 9.7 years), who underwent resective surgery for the intractable epilepsy from 2010 to 2012 were retrospectively studied. Seizure types consisted of epileptic spasms in nine patients, partial seizures in 17 patients and partial seizure with secondary generalization in four patients. Eight autopsy cases without neurological disease served as controls. The neuropathology examination utilized the H&E/LFB stain and immunohistochemical staining for NeuN, GFAP and Olig2 as a marker of OLCs. OLCs were counted in three sites: (a) gray matter, (b) junction of gray/white matter, and (c) white matter. We also examined the correlation between the density of OLC among the three sites and the clinical features. Fifteen (50%) patients underwent multiple lobe resections, consisting of both temporal and extratemporal lobe resections in 12 patients and extratemporal lobe resections in 3 patients. The other 15 (50%) patients underwent single lobe resection including 3 (10%) patients with temporal lobectomy sparing hippocampus. Pathological diagnosis of epilepsy patients was as follows: 14 (47%) patients=focal cortical dysplasia (type I, 4; II, 9; III, 1); 6 (20%)=oligodendrogliosis; 6 (20%)=astrocytic gliosis; 2 (7%)=hyaline protoplasmic astrocytopathy and 2 (7%)=tuberous sclerosis complex. The numbers of OLCs at all three sites in epilepsy group were significantly higher than those of control group (p<0.001). In the epilepsy group, there was a significant difference among the number of OLCs at gray matter, junction of gray and white matter, and white matter (p<0.001). The number of OLCs significantly increased from gray matter and junction of gray/white matter to white matter. In the control group, there was no difference among the number of OLCs at three sites. There was no significant difference in the numbers of OLCs between focal cortical dysplasia types I and II. The significantly increased OLCs, especially in the white matter may contribute to the extensive epileptic network in children with intractable focal epilepsy.