Elektrophysiologische Indizes der Informationsverarbeitung bei Patienten im 'Vegetativ State' und 'Minimally Conscious State' : Auftretensmuster und klinischer Vorhersagewert

Abstract

In this study we examined the development of 92 patients in a vegetative state or a minimally conscious state. The patients were hospitalised between 1995 and 2005 in the Kliniken Schmieder, Allensbach. 53 of the patients had been in a vegetative state (VS) at the date of their initial examination, 39 had been in a minimally conscious state (MCS). In our research we focused on the existence and prognostic value of two so called late and therefore cognitive event related potentials (ERPs): the P300 and N400.We recruited former patients for a follow-up study, 2 to 13 years after they were discharged from the rehab hospital. The patients that were still alive were visited and we measured their condition with the glasgow outcome scale . For the deceased patients we tried to elicit information about the patient s last condition from their relatives. Clinically we find that after the follow-up time (of 2 to 13 years) around 50% of the patients were deceased, 25% showed no progress and 25% of the patients' condition improved. We also find that patients with a traumatic cause did improve more often and to a better outcome than patients with a hypoxic cause. And we find that VS and MCS patients did not significantly differ in their ability to improve.In case of the P300, we find that patients in MCS and VS did show this ERP. But it did not yield any prognostic value. Meaning the condition of patients showing a P300 did not improve more frequently than patients who did not show the component.That picture is completely different in case of the N400 component. The N400 typically occurs as a result of semantic incongruity. Here we find a positive correlation between a detectable N400 and a later positive development of the patients. This correlation holds true for patients in a VS and a MCS.The main finding of the study is that contrary to claims in past publications more patients in a VS are able to produce an N400. It will help to improve our understanding of information processing by patients with very limited consciousness.Another important finding is that the N400 component can be used to predict the awakening from the vegetative state and the regaining of (rudimentary) communication abilities.