By Susan Fitzgerald
Transcranial direct current stimulation (tDCS), a non-invasive medium for cortical stimulation using weak polarizing currents, may temporarily improve signs of consciousness in brain-damaged patients who are in a minimally conscious state (MCS), according to a randomized-controlled trial from Belgium published in the Feb. 26 online edition of Neurology.
After a short session of tDCS was delivered over the left prefrontal cortex, MCS patients showed improvement as measured by a standardized scale, but the electrical stimulation did not, for the most part, help persons in a vegetative/unresponsive wakefulness syndrome (VS/UWS) who only show reflex movements. The electrical stimulation was compared with a sham treatment.
The improvement in signs of consciousness that was measured right after treatment was not evident when the patients were reassessed 12 months later. The study’s senior author, Steven Laureys, MD, PhD — director of the Coma Science Group and clinical professor of neurology at University Hospital of Liege in Belgium — told Neurology Today that caution was needed to avoid presenting the study results as “spectacular changes.”
“It is a real yet moderate effect and should not give false hopes to families,” Dr. Laureys said in an e-mail.
An editorial accompanying the study in the same edition of Neurology noted “the article is of considerable interest as it suggests another potential treatment avenue for DOC [disorders of consciousness], as well as suggesting a promising site of intervention.” The editorial stressed that more research was needed to determine whether these short-term effects can be amplified and made more durable, which would be required for real clinical effectiveness.”
The Belgium study included 55 brain-damaged patients, 30 with MCS and 25 with VS/UWS, who were hospitalized in the neurology department of the University Hospital of Liege or at a rehabilitation center. The study group, ranging in age from 15 to 85, had heterogeneous causes of brain damage. Some of the patients had suffered a traumatic brain injury; in other cases, the damage was due to a non-traumatic event such as a subarachnoid hemorrhage or anoxia. The time since brain damage ranged from seven days to 26 years.
The study was a double-blind sham-controlled design in which anodal and sham tDCS were delivered by randomized order over the left dorsolateral prefrontal cortex for 20 minutes.
Patients were assessed using the Coma Recovery Scale Revised (CRS-R) — a scale that goes from 0 to 23, with the higher score meaning higher awareness or demonstration of cognitively mediated behaviors — directly before and after anodal and sham stimulation. They also were assessed 12 months later with the Glasgow Outcome Scale-Extended to determine the long-term effect of tDCS.
“Responders” were defined as those patients who after receiving tDCS presented a sign of consciousness — intentional or functional communication, command following, visual pursuit, recognition, manipulation, localization or functional use of objects, or orientation to pain — that was not present before the treatment or before or after a sham treatment.
The article reported that 13 of the 30 MCS patients (43 percent) showed some improvement after tDCS. Five of the 13 MCS responders were at least five months post-injury. In the VS/UWS group, two patients (8 percent) showed a response. Both of them were less than three months post-injury.
“No correlation between tDCS response and patient outcome was observed at 12 months follow-up,” the team reported.
“Our study illustrates the residual capacity for neural plasticity and temporary recovery of (minimal) signs of consciousness in some patients in MCS, but does not permit us to make any claims regarding possible long-term tDCS effects in this setting,” the study authors noted.
Stay tuned for the full discussion of the findings and their implications in the April 3 issue of Neurology Today. See our previous coverage of research involving patients in MCS: http://bit.ly/1o1Azwl.