May clinical neurophysiology help to predict the recovery of neurological early rehabilitation patients brain anoxia

Background

Patients entering neurological and neurosurgical early rehabilitation are severely impaired. Morbidity is high [ 1] and they are suffering from disorders of consciousness [ 2, 3]. Early rehabilitation patients are dependent on nursing and may be colonized with multi-drug resistant germs [ 4, 5]. Frequently, their outcome is poor, but it is quite difficult to predict outcome accurately [ 3].

The role of clinical neurophysiology, in particular electroencephalography (EEG) and evoked potentials (EP) in predicting outcome of these patients is still unclear. Only a few studies are available on long-term rehabilitation results and clinical neurophysiology.


The question is whether clinical neurophysiological techniques may help to distinguish between patients who benefit from neurological early rehabilitation and such who don’t.Brain anoxia in contrast to imaging techniques, neurophysiological measurements are easy to perform, cheap, safe and available in most rehabilitation facilities.

Most studies focus on rehabilitation outcome of stroke patients (table 1) [ 6– 16]. With respect to SEP, an absence or amplitude reduction of cortical responses seems to be associated with a poor long-term outcome after stroke [ 6, 7, 10]. Like with SEP, absence of MEP may indicate poor recovery from stroke [ 10, 16]. VEP have also been studied, suggesting that left-right asymmetry may be associated with functional outcome [ 9]. Presence of delta and theta activity in EEG predicted unfavorable outcome one year after stroke [ 8].

AEP

AEP data was available in 448 cases (55.8 %).Brain anoxia absence of AEP on one side was observed in two cases, bilateral loss of AEP responses in one case, only. All three cases belonged to the poor outcome group, but due to small sample size, χ 2-test did not reveal significant differences. When comparing poor and good outcome groups, it turned out that a significantly longer latency III was observed on both sides in the poor outcome group ( p 0.05), table 8. Latency IV also showed significant differences between the groups, but on the left side, only ( p 0.05). Since AEP are closely connected to brain stem function, a sub-analysis focusing on brain stem lesions was done: 60 patients with brainstem lesions (7.5 %) were identified. With intact brain stem, BI at discharge was significantly higher than in patients with uni- or bilateral lesion ( F = 3.931, p = 0.009).Brain anoxia further, there was a small but significant correlation between age and AEP latency III (left: r = 0.209, p 0.001; right: r = 0.132, p 0.01).

Discussion

So far, reliable data on the usefulness of neurophysiological measurements in predicting the outcome from neurological and neurosurgical early rehabilitation is lacking. The present study analysed data of a large sample 803 patients. One would opt for clinical neurophysiology as a predictor because it is cheap, safe (no radiation), easy to perform and available in most rehabilitation facilities (in contrast to imaging like CT or MRI).

As with previous studies, present results suggest that outcome of neurological early rehabilitation patients mainly depends on age, morbidity and functional status on admission [ 3].Brain anoxia however, neurophysiological data may be of some predictive value, in particular median SEP, AEP, flash VEP and EEG.

It turned out that patients with worse outcome had longer AEP III latencies. AEP wave III represents the cochlear nucleus which is located in the pontomedullary junction of the dorsolateral brainstem [ 35]. It is well known that brainstem lesions are associated with poor neurological outcome and fatality [ 36]. This finding could be reproduced in this study: subjects with brain stem lesions on one or both sides showed a worse functional outcome from neurological early rehabilitation. As yet, a prolongation of AEP wave III latency has not been identified as a predictor of poor outcome and is a novel finding.Brain anoxia age, however, correlated significantly with wave III latency. Since age is a well-known predictor of poor outcome in neurological rehabilitation [ 3], it may partially explain this finding. In addition, it has to be pointed out that even in the normal ageing brain, a delay of evoked potentials, in particular VEP and AEP, may be observed [ 37, 38].

Another finding of this study was a prolongation of wave III in flash VEP in the poor outcome group. This finding is in line with a previous study from our group which focused on hypoxic brain damage patients [ 3]. VEP wave III abnormalities might be a neurophysiological correlate of cortical dysfunction [ 3]. As with AEP, VEP wave III latency also correlated with age.Brain anoxia thus, age might influence AEP wave III, too.

Another finding was that loss of cortical median SEP responses on one or both sides was associated with poor outcome. We know from literature that long-term outcome of stroke patients is also worse with absent SEP [ 6, 10]. Thus, it may be hypothesized that absence of SEP indicates poor outcome in early rehabilitation patients.

There are a couple of studies focusing on EEG and outcome prediction. As with previous studies [ 3, 8], theta and delta activity was associated with poor outcome.

There are some limitations to this study. First of all, this was a retrospective data analysis, only. This explains why only a proportion of the sample has been studied with all four neurophysiological examinations (EEG, SEP, AEP, VEP).Brain anoxia secondly, the patients showed a wide heterogeneity. This, however, is a common finding when examining neurological early rehabilitation patients [ 1]. These patients suffer from a broad specter of neurological and neurosurgical disorders, central as well as peripheral disturbances. In addition, the study employed no control group and confounding medication (e.G. Neuroleptics, benzodiazepines) has not been included in the analysis. Sedatives, however, are rarely used in our rehabilitation facility.

Results from this study defy ready summary, but EEG, median SEP, AEP and flash VEP may be of some predictive value in early rehabilitation patients. Further studies are strongly encouraged.