Neurophysiological and anatomical correlations in neonatal nonketotic hyperglycinemia

Electroencephalographic (EEG) and brainstem auditory evoked response (BAER) findings have not been previously described and correlated with the pathological findings in an autopsied case of neonatal nonketotic hyperglycinemia (NKH). A 38 week gestation male infant presented within two hours of age with stimulus-evoked myoclonus and seizures in the context of progressive coma. Electrographic studies demonstrated cortical myoclonus and electrical seizures exquisitely localized to the midline region as well as a suppression-burst background disturbance. These vertex spike discharges were elicited after tactile stimulation. Prolonged intra-axial latencies for waves III and V were recorded on the BAER on the second day of life. Spongy leukodystrophy was noted on gross and microscopic examination of the brain involving all myelinated tracts especially in the reticular activating system, cerebellar peduncles and optic tracts. Neuropathological confirmation of brainstem involvement emphasizes the role of the nonspecific diffuse somatosensory projection system in the generation of myoclonus and stimulus-evoked seizures in the comatose patient with NKH.