EEG abnormality grades and subdivisions of prognostic importance in traumatic and anoxic coma in adults

The EEG has long been established as an important laboratory test when assessing cerebral function in comatose states. During the last three decades, several grading scales regarding severity of the EEG abnormality in coma have been suggested to increase the prognostic power of the EEG for survival. Their main limitation was, that the majority of EEG abnormalities in coma fell in the middle of the five point scaling systems, i.e. Grade 3 abnormality on the five grade abnormality scales. In addition, it was considered that non-reactivity of EEG pattern in coma is confined only to the most advanced grades. The purpose of the present article is to define precisely the main five abnormality grades and their subdivisions, and to allocate them in five principal categories regarding their significance for survival. The five categories are: 1 = optimal, 2 = benign if persistent, 3 = uncertain, 4 = malignant if persistent, and 5 = fatal unless caused by drug effect or hypothermia. After the inclusion of more recently described coma patterns, it was possible to outline prognostic significance for survival in eleven types of abnormalities with assurance. Only four remain of uncertain prognostic significance. The EEG abnormalities as discussed in this article are generally applicable only to coma after diffuse brain trauma and cerebral hypoxia. However, they may also be found in some other diffuse encephalopathies associated with coma.