The prognostic value of three-modality evoked potentials (TMEPs) in anoxic and traumatic comas

Abstract

Three-modality evoked potentials (TMEPs) were recorded in 184 comatose patients (52 anoxic, 132 traumatic). Both types of comas were associated with different TMEP patterns. Anoxic comas were associated with prognostically relevant abnormalities of cortical (visual and somatosensory) evoked potentials (EPs), while brainstem (auditory and somatosensory) EPs were not specifically altered. The prognostic value of TMEPs in anoxic comas depended on the time elapsed from the acute episode: mildly altered EPs were associated with a better prognosis in the first 10 days; strongly altered TMEPs were associated with a poorer prognosis from the first day; no definite conclusion could be drawn from mildly altered EPs after the 10th day, or from strongly altered TMEPs in the first 24 h. By contrast, both the cortical and the brain-stem activities were altered in head trauma. The abnormalities were clustered into four patterns: hemispheric damage without brain-stem involvement (pattern 1), mesencephalic lesion (pattern 2), transtentorial herniation (pattern 3), and brain death (pattern 4). Patterns 3 and 4 were uniformly associated with death. The prognostic value of pattern 1 was similar to that observed in anoxic comas. The outcome of patients presenting pattern 2 depended on the extent of hemispheric damage associated with the mesencephalic lesion; we thus suggest to systematically perform magnetic resonance imaging (MRI) in patients presenting TMEP pattern 2. We finally demonstrated that a few patients presenting absent cortical activities in the very acute stage of coma can eventually recover a good neurological function.