title: Clinical evidence supporting a subthalamic origin of the P15 wave of the somatosensory evoked potentials to median nerve stimulation.
abstract: Both somatosensory (SSEPs) and brain-stem auditory evoked potentials (BAEPs) were recorded in 3 patients with localized lesions in the thalamus or brain-stem. In one patient with a right thalamic cystic tumour there was a significant interhemispheric difference in the central conduction time (CCT), but the N14-P15 interval was not affected on either side and BAEPs showed normal wave latencies and interpeak latencies (IPLs). The second patient had a colloid cyst of the third ventricle in which central herniation had occurred resulting in 'locked-in' syndrome. The P15 peak was absent on one side and markedly prolonged in latency on the other. BAEPs showed neither wave IV nor V on either side. The third patient had compression of the right posterior rostral pons by a metastatic tumour, resulting in significant prolongation of the CCT on the side of the tumour because of increase in the N14-P15 interval. Both I-V and III-V interpeak latencies were significantly prolonged bilaterally without prolongation in I-III IPL in this case. There was a correlation between the electrophysiological abnormalities of P15 and of BAEP wave V. These results suggest that the origin of the P15, which is usually recorded as a far-field potential, may be in the subthalamus or the upper part of the brain-stem.
mesh_terms: D000328:Adult; D000368:Aged; D001927:Brain Diseases / Q000000981:diagnostic imaging; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000556:secondary; D001933:Brain Stem / Q000503:physiopathology*; D003560:Cysts / Q000000981:diagnostic imaging; D004027:Diencephalon / Q000503:physiopathology*; D005072:Evoked Potentials, Auditory; D005073:Evoked Potentials, Somatosensory; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008875:Middle Aged; D009431:Neural Conduction; D013997:Time Factors; D014057:Tomography, X-Ray Computed