The prognostic value of somatosensory and motor evoked potentials in comatose patients

Somatosensory and motor evoked potentials (SEP and MEP) were examined in a total of 213 patients in traumatic (n = 140) and nontraumatic (n = 73) coma. It was the aim of this study to compare the prognostic value of MEP elicited by both electrical and magnetoelectric transcranial stimulation with the use of SEP alone. According to the presence or absence of responses and the duration of central conduction time, SEP and MEP obtained during Days 1 through 3 after the onset of coma were divided into four categories and correlated with the outcome of the patients, as assessed by the Glasgow Outcome Scale. Our results clearly show that in terms of prognostic value, SEP are superior to MEP, with normal findings indicating a favorable outcome and absent responses an unfavorable outcome. On the other hand, patients with normal electromyographic responses after both electrical and magnetoelectric stimulation had favorable and unfavorable outcomes about equally. Thus, unlike SEP, normal MEP do not allow any prognostic conclusions. Only the bilateral absence of MEP in response to electrical stimulation was a definitely unfavorable prognostic sign because all of these patients died. In contrast, with magnetoelectric stimulation, neither normal nor absent responses allowed any prognostic conclusions. Therefore, the prognostic value of electrically evoked motor responses is limited, and magnetoelectric stimulation cannot be recommended in this context.