Anoxic-ischemic alpha coma: prognostic significance of the incomplete variant.

Abstract

The prognostic significance of post-anoxic-ischemic alpha coma (AC) is controversial. We recorded somatosensory evoked potentials (SEPs) and performed serial electroencephalography (EEG) in a 60-year-old woman in coma after cardiac arrest. The first EEG was recorded after 48 hours (GCS=5; E1-V1-M3); brain-stem reflexes were preserved. The EEG pattern showed monotonous alpha frequencies (10-11 Hz) with posterior predominance; acoustic and noxious stimuli evoked EEG reactivity. Early cortical SEPs (72 h) were normal. On the fifth day (GCS=8; E4-V1-M3), the EEG alpha pattern was replaced by a diffuse delta activity; rhythmic theta changes appeared spontaneously or in response to stimuli. The patient regained consciousness on the tenth day and EEG showed posterior theta activity (6-7 c/s) partially reactive to stimuli. At the 6-month follow-up, cognitive evaluation showed mild dementia. Recent studies identified two forms of AC. Patients with complete AC have an outcome that is almost invariably poor. Conversely, incomplete AC (posteriorly accentuated alpha frequency, reactive and with SEPs mostly normal) reflects a less severe degree of anoxic-ischemic encephalopathy. The case we report should be classified, according to the SEPs and EEG features, as incomplete AC. The fact that the patient has regained consciousness, even if with residual cognitive impairment, confirms the need to distinguish this variant from complete AC.