ELECTROPHYSIOLOGICAL STUDIES ON BRAIN-STEM FUNCTION IN PATIENTS WITH MYELOMENINGOCELE

We investigated the brainstem auditory evoked potentials (BAEPs), somatosensory evoked potentials (SEPs), and electrically elicited blink reflexes (BRs) to evaluate the brainstem function in 31 patients with myelomeningocele (MMC) including 22 with Chiari type-II malformation. The I-III interpeak latency (IPL) of the BAEPs and the N-9-N-13 IPL of the SEPs tended to become gradually prolonged from the normal range with increasing age. The III-V IPL of the BAEPs and the N-13-N-20 IPL of the SEPs were initially prolonged and decreased progressively to the normal range. These findings indicated a gradual latency shortening of the brainstem components and latency prolongation of the peripheral components. Thus, while primary brainstem dysfunction may improve with age, secondary dysfunction due to stretching and elongation of the lower cranial nerves and cervical nerve roots may intensify. The BRs showed an abnormal R(2) in 90% of the cases, disclosing subclinical lesions in the medulla oblongata which were not detected by BAEPs alone. BAEPs, SEPs and BRs were combined to yield a functional evaluation of the brainstem and lower cranial nerves that could not be done by magnetic resonance imaging alone. No close relation was found between electrophysiological abnormalities and the degree of hindbrain anomaly by neuroimaging.