Brainstem diagnosis via somatosensory-evoked potentials following stimulation of the median nerve

Isolated, specially vascular-MRI-detected brainstem lesions were used to analyse the generator sources of somatosensory evoked brainstem potentials after stimulation of the median nerve. According to these findings somatosensory evoked far-field potentials can support the diagnosis of functional disturbances in these regions of the brainstem in individual patients. The generator source of the far-field P14 potential is localised within the medial lemniscus. For brain-death diagnosis, recording of the P14 potential by nasopharyngeal electrode may also be useful. An additional potential of the brainstem, N18a, is discussed as being generated in the upper brainstem. Intravascular recordings in the basilar artery and recordings around the brainstem point to a mesencephally localised origin of the N18a potential. In patients with Chiari 11 malformation, the recordings of the somatosensory evoked P14 and N18a potential after median nerve stimulation support the clinical diagnosis of a symptomatic patient. Simultaneously, near-field recording is recommended to exclude additional spinal or peripheral anomalies. Hence, simultaneous 4-channel technique is required to analyse the somatosensory evoked brainstem potentials after median nerve stimulation.