September 25, 2017

expert reaction to study looking at vagus nerve stimulation in a patient in a vegetative state

Researchers publishing in Current Biology report that a 35 year-old man who had been in a vegetative state for 15 years has shown signs of consciousness after neurosurgeons implanted a vagus nerve stimulator into his chest.

Dr Vladimir Litvak, Senior Lecturer, The Wellcome Centre for Human Neuroimaging, UCL Institute of Neurology, said:

“This might be an interesting new lead but I would suggest to be cautious about these results until they are reproduced in more patients.  It is hard to know based on a single case how likely this treatment is to work in the general patient population.  Furthermore, a minimally conscious state still constitutes severe disability and the authors of the paper had to use special clinical tests and neuroimaging measures to prove that there has indeed been a change in the patient’s state.  This suggests that the practical implications for this patient’s care were minor if any.

“In 2007 a paper making similar claims was published in Nature (Schiff et al. ‘Behavioural improvements with thalamic stimulation after severe traumatic brain injury’).  The patient described in that paper had more dramatic behavioral improvements (for instance was able to start eating on his own) but this result has not been translated to a commonly used therapy to date.”

Dr David McGonigle, Neuroscientist, Cardiff University, said:

“It is important to recognise that this study, while promising, is a single case study only.  Vagal nerve stimulation may not work as effectively in other vegetative state patients, as individual patterns of brain damage may limit its potency.  We must also recognise that, while the study presents a number of brain imaging measures that show differences between the pre- and post-stimulation phases in the patient, actual behavioural improvement, as measured by the CRS-R, is reasonably small.  Evaluating the effectiveness of a treatment when you only have a single, albeit impressive, result is tricky, if not impossible: a full randomised controlled clinical trial is really needed to fully evaluate the effectiveness of vagal nerve stimulation in people in a vegetative state.”

Dr Elizabeth Coulthard, Consultant Senior Lecturer in Dementia Neurology, University of Bristol, said:

“This is a single patient study that, on the face of it, suggests stimulating the vagal nerve led to improved function in a patient persistent vegetative state.  The score used to assess function here is a 23 point scale where 0 represents no real verbal, visual or motor response and 23 indicates good ability, for example, appropriate responses to commands and intelligible speech.  At the start of the study, before any stimulation, the patient scored 6/23 and at the end of the study, when the patient was on the maximum stimulation, he scored 8/23 on the functional scale.  At times during the 6 month period, the patient scored as high as 10/23.  This is a very small performance difference that is of questionable significance to the patient.  The effects of stimulation on brain activity were statistically related to the functional abilities of the patient which may suggest that the stimulation directly caused the improved functional scores, but when the patient was on the maximum stimulation, he scored between 6 and 10 on the functional scale.  So the effects of stimulation were not consistent and, if present, may not continue in the long term.

“While it is suggested that perhaps this opens an avenue for future research, one cannot infer any clinical benefit on the basis of this one patient.  Even the small change demonstrated here may not be transferable to other people in a persistent vegetative state.”

* ‘Restoring consciousness with vagus nerve stimulation’ by Martina Corazzol et al. published in Current Biology on Monday 25 September 2017.

Declared interests

Dr David McGonigle: “I am involved in non-invasive brain stimulation work in normal human participants.  I have no links to the authors (have never met any either) and have no financial links to any other treatments/devices etc.).”

None others received.