Idiopathic generalized epilepsy: lack of significant microdysgenesis

The idiopathic generalized epilepsies (IGE) are classically regarded as due to a functional abnormality. However, microscopic microdysgenetic changes have been reported in the majority of cases by one group.

To independently evaluate the microscopic microdysgenetic changes in a controlled, blinded study.

Five brains with IGE and five age-matched control brains were collected. Blocks were taken from nine standardized Brodmann areas, both hippocampi, and cerebellum. Slides were examined independently by two neuropathologists blinded to patient group, who qualitatively scored microdysgenetic features on standardized data sheets. The results were compared and any discrepancies were rescored by the pathologists together using a double-header microscope. Quantitative neuronal profile counts in the molecular layer in standardized Brodmann areas of frontal cortex and in deep frontal white matter were performed.

Microdysgenetic features in nine Brodmann areas, hippocampi, and cerebellum were not increased in brains from subjects with IGE compared with control brains. Quantitative neuronal profile counts in the molecular layer of frontal cortex and deep frontal white matter were not increased in IGE compared with controls.

This controlled, blinded study did not replicate the results of previous reports of microdysgenesis in IGE. Although factors such as syndrome heterogeneity and sample size may explain the discrepancy, technical factors could also play a role. The current ion channel hypothesis for the pathogenesis of IGE does not preclude microscopic or ultramicroscopic abnormalities and the search for these should continue.