Giant somatosensory evoked potentials are uncommon in patients with post-anoxic coma and paroxysmal electroencephalographic activity

Abstract

Objectives Post-anoxic encephalopathy (PAE) is a severe neurological condition associated with poor outcome. As part of a multi-modal evaluation, electrophysiological investigations such as electroencephalography (EEG) and somatosensory evoked potentials (SSEPs) have been shown to be reliable outcome predictors in the assessment of comatose survivors, particularly with PAE [3] . The aim of the study was firstly to evaluate the feasibility of performing SSEPs in post-anoxic comatose patients with paroxysmal activity on EEG and secondly to assess the relationship between EEG cortical hyperexcitability and giant cortical N20 SSEPs responses. Methods In this retrospective study between 2016 and 2018, patients with PAE, paroxysmal activity on EEG and available median nerve SSEPs data were included in the analysis. Paroxysmal activity was identified on the EEG performed in the last 48 h preceding SSEPs. We evaluated the N20 amplitude from baseline, and P14-N20 and N20-P24 peak to peak amplitudes. Giant SSEPs were defined as a N20 exceeding 2.7 μV or N20–N24 exceeding 5.5 μV [2] or a late giant component exceeding 5 μV [1] . Results Twenty-one patients were included; 14 men (67%) mean age 66 ± 18 years. A total of 62% of PAE cases were due to cardiac arrest. Nineteen patients died following withdrawal of life support, one died spontaneously and one patient survived. Three patterns of EEG paroxysmal activity were identified: continuous rhythmic activity (n = 3), periodic generalized discharges (GPDs) on a low frequencies background (n = 12) and GPDs on a flat background (burst-suppression) (n = 6). SSEPs were giant in 3 patients (14%), normal in 7 patients (34%), reduced in 3 patients (14%) and absent bilaterally in 8 (38%). Conclusions Our study shows that performing SSEPs is feasible in PAE patients with EEG paroxysmal activity. Giant SSEPs are uncommon in these patients. The EEG cortical hyperexcitability reflects different stages of brain injury, as it can be associated with preserved (even giant), or absent SSEPs.