Brain-stem somatosensory dysfunction in a case of long-standing left hemispherectomy with removal of the left thalamus: a nasopharyngeal and scalp SEP study

We have studied median nerve somatosensory evoked potentials (SEPs) in a patient who had undergone early surgical removal of the left cerebral hemisphere and left thalamus. Stimulation of the right side evoked normal latency P9, P11 and P13 potentials at scalp as well as at nasopharyngeal (NP) leads, while P14 and N18 potentials were absent. These SEP abnormalities, that have been described previously in cervico-medullary lesions and in comatose patients with upper brain-stem involvement, suggest that in our patient the removal of the left thalamus has caused retrograde degeneration of the cuneate-thalamic projections. Moreover, this study confirms that P13 and P14 potentials have different generators.