The prognostic value of somatosensory evoked potentials in traumatic primary and secondary brain stem lesions

To estimate the prognostic value of somatosensory evoked potentials elicited via stimulation of the median nerve (M-SSEP) in cases of primary and secondary brainstem lesions 126 patients with traumatic brainstem lesions (GCS < or = 6) were investigated on admission to our hospital. Various parameters of the patients' M-SSEP were compared with the corresponding data of 40 healthy persons. Latency and amplitude of the cervical (N14) and cortical (N20) derived potentials and the central conduction time (CCT) were taken into account. Changes or a loss of the N20 signal and of the CCT were related to clinical outcome for up to two years. All patients had a normal N14 bilaterally. Most patients with a primary brainstem lesion (n = 25) showed symmetrical N20 changes bilaterally. However, the majority of patients with a secondary brainstem lesion (n = 62) showed asymmetric N20 changes in M-SSEP which became more symmetrical in cases with marked progressive brainstem compression. Irrespective of a primary or secondary traumatic brainstem lesion, marked changes of N20 represented an unfavourable clinical prognosis. A loss of N20 was closely correlated with a very poor outcome (GOS 1-2) if the N20 potential had not recovered within 48 hours. The recovery of this potential, however, was not necessarily correlated to a recovery of the brain function.