EEG in the Evaluation of Patients with Coma and Other Disorders of Consciousness

Robert C. Knowlton, MD, MSPH Reviewing Forgacs PB et al., Ann Neurol 2014 Dec 76:869

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Standard bedside electroencephalography provides complementary information in the assessment of unrecognized cognitive function in severely brain-injured patients.

The clinical evaluation of disorders of consciousness involves the challenge of distinguishing coma from vegetative state (VS) and from minimally conscious state (MCS).

Recent neuroimaging studies have revealed cases with remarkable findings that diverge from bedside examination, suggesting that some patients are in a state more like locked-in syndrome rather than either VS or MCS.

To examine the value of electroencephalography (EEG) in making these distinctions, researchers now report findings of a prospective cohort study of 44 patients with disorders of consciousness assessed at least once with overnight continuous EEG. Most patients also underwent functional magnetic resonance imaging to examine covert command-following and fluorodeoxyglucose–positron emission tomography to measure and depict cortical metabolism. The study focused on correlations between conventional EEG analysis and behavioral and neuroimaging measures of brain function.

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The main findings were that  EEG features correlate with overall brain metabolism and behavioral diagnosis, and all patients with covert command-following had normal or mildly abnormal EEG background activity.

The most diagnostically valuable EEG features were relative preservation of background architecture and well-developed sleep spindles. The authors conclude that conventional visual assessment of EEG organization accurately measures overall brain activity and may aid the evaluation of patients with disorders of consciousness.

This study provides evidence supporting the clinical value of conventional EEG in the challenging evaluation of patients with disorders of consciousness.

The authors appropriately emphasize that EEG is widely available, inexpensive, and, for this purpose, requires only standard visual interpretation. Limits to diagnostic accuracy remain, but EEG assessment of corticothalamic integrity can aid the overall evaluation.

Clinical suspicion of some degree of cognition and awareness should be raised in patients with disordered consciousness who have a normal or mildly abnormal EEG along with high risk of motor-system injury based on etiology and history.

Conversely, patients with severely abnormal EEG background activity are highly unlikely to have any meaningful cognitive function.

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