Non-invasive SEP performed at the bedside of more than 150 patients in coma from different causes has proved to have both diagnostic and prognostic value. Combining information generated in 3 modalities: somatosensory (SSEP, on its own the most important), flash visual (FVEP), and brain-stem auditory (BAEP), allows the evaluation of patients with CNS diffuse lesions through a ‘vertical’, a ‘horizontal’ and a brain-stem view. SEPs contribute to the diagnosis of pathway lesions, neurophysiological level of lesion, brain death (in association with EEG).
Establishing prognosis is perhaps the best contribution of SEP in coma:
(1) abnormal BAEP (brain-stem lesion) reserved prognosis; a normal BAEP does not allow precise definition, depending on others SEP;
(2) bilaterally normal or only slightly altered SSEP, good prognosis; bilaterally absent Pl4 together with absent BAEP may be compatible with brain-stem death, or with brain death if accompanied by absent FVEP and electrocerebral silence in the EEG; bilateral absence of thalamo-cortical (N20 and P25) components, bad prognosis, since the best outcome (in younger patients) was to a persistent vegetative state; adults and older patients died; intermediate SSEP corresponded to intermediate prognosis;
(3) FVEP has shown the same prognostic tendency as SSEP, but with a lesser degree of precision.