Abstracts

Rationale: Proinflammatory and anti-inflammatory molecules produced by glia have been shown to play an important role in neuronal excitability and the occurrence of seizures. Astrocytes release glutamate and can initiate a paroxysmal depolarization shift. Microglia, as both the primary source and target of many cytokines and chemokines in the CNS, are also poised to take a central position in the seizure-induced inflammatory response. To determine the contribution of glial activation in intractable childhood epilepsy, we histologically analyzed the distribution and quantity of microglia, astrocytes, and neuronal injury in resected brain tissue from children undergoing surgery for localization-related epilepsy with diverse etiologies.Methods: Cortical tissues from eight patients with chronic intractable epilepsy were collected from January 2006 to March 2007 at Children's Memorial Hospital Northwestern University. Controls were autopsy samples from four patients without history of seizures or other neurological diseases. Representative sections were processed for immunocytochemistry using neuronal (NeuN) and glial markers (GFAP, CD68) and adjacent sections were processed for in situ nick translation histochemistry for DNA fragmentation to assess neuronal injury. We used an image analysis system, MetaMorph (v. 6.1, Universal Imaging Corp.), for quantification.Results: The age at epilepsy surgery of eight patients ranged from 2.4 to 19.5 years and the duration of epilepsy, 0.4 to 16.5 years. Etiologies of chronic intractable epilepsy included Rasmussen’s encephalitis (1), focal cortical dysplasia (3), and encephalomalasia (total 4) due to intrauterine stroke (2), traumatic brain injury (1), or previous resection of giant cell astrocytoma (1). Astrocytes were markedly increased in the cortical gray matter of all 8 patients (100%) (p<0.001). Diffuse GFAP-positive-astrocytes in the cortical mantle blurred the boundary between the white matter and gray matter in the surgical specimens from epilepsy patients. Abundant cell death was found in 88% (7/8) of patients (p<0.001). Microgliosis was present in 75% (6/8) of patients. Microglia were significantly increased in both gray and white matter in the Rasmussen’s encephalitis and 2/3 of patients with cortical dysplasia (3/8, 37.5%) (p<0.001). Increase in microglia was limited to the white matter in 3/4 of patients with encephalomalasia (p<0.001). Conclusions: Astrogliosis and cell death were common findings among pediatric patients with intractable epilepsy of different etiology. While microglial activation was most prominent in Rasmussen’s encephalitis, significant microgliosis was also observed in the focal cortical dysplasia and in the white matter of encephalomalasia. Our result provides the evidence for an involvement of activated glia in chronic intractable childhood epilepsy. Astrogliosis and microgliosis may be a common factor and play a contributory role in epileptogenesis. Our data suggest a potential role for anti-inflammatory therapy to prevent the development of chronic intractable epilepsy in children.