Burst suppression and impairment of neocortical ontogenesis: electroclinical and neuropathologic findings in two infants with early myoclonic encephalopathy.

We report the electroclinical and neuropathologic correlations in 2 children aged 2.5 months affected by early myoclonic encephalopathy characterized by epileptic seizures, erratic myoclonus, and an EEG pattern of burst suppression. Despite different etiologies, the neuropathologic findings showed similar abnormalities in both cases, with no substantial impairment of the myelination processes. Islands of matrix tissue scattered in the periventricular region and neurons aligned marginally in the bulbar olives were detected. The presence of numerous large spiny neurons dispersed in the white matter along the axons of the cortical gyri was the most striking finding. The neurons have been interpreted as abnormally persisting interstitial cells in 2.5-month-old children. These early generated neurons, normally present during neocortical histogenesis, are programmed to die near the end of gestation or soon after birth. The interstitial cells are regarded as a waiting compartment of afferent fibers during cortical development. Their persistence in our patients represents an anatomic condition for cortical disconnection providing a pathophysiologic basis to burst-suppression phenomena.