Subcortical somatosensory evoked potentials after posterior tibial nerve stimulation in children.

We report our normative data of somatosensory evoked potentials (SEP) after posterior tibial nerve (PTN) stimulation from a group of 89 children and 18 adults, 0.4-29.2 years of age. We recorded near-field potentials from the peripheral nerve, the cauda equina, the lumbar spinal cord and the somatosensory cortex. Far-field potentials were recorded from the scalp electrodes with a reference at the ipsilateral ear. N8 (peripheral nerve) and P40 (cortex) were present in all children but one. N20 (cauda equina) and N22 (lumbar spinal cord) were recorded in 94 and 106 subjects, respectively. P30 and N33 (both waveforms probably generated in the brainstem) were recorded in 103 and 101 subjects, respectively. Latencies increased with age, while central conduction times including the cortical component, decreased with age (up to about age 10 years). The amplitudes of all components were very variable in each age group. We report our normative data of the interpeak latencies N8-N22 (peripheral conduction time), N22-P30 (spinal conduction time), N22-P40 (central conduction time) and P30-P40 (intracranial conduction time). These interpeak latencies should be useful to assess particular parts of the pathway. The subcortical PTN-SEPs might be of particular interest in young or retarded children and during intraoperative monitoring, when the cortical peaks are influenced by sedation and sleep, or by anesthesia.