In the netherworld that lies between death and full consciousness, some grievously injured or ill patients will remain suspended indefinitely. But others, given time, will eke their way out of the twilight and toward recovery. Accurately predicting which group an apparently vegetative patient falls into could bring comfort, solace and sometimes hope to their families — and also to the patients involved, who may wish to convey they are still "in there," or may feel pain that is not being addressed.
Developing a test that could foretell the long-term outcome of a stricken patient has proved elusive. But a new study finds that scans that look for signs of metabolic activity in certain regions of the brain can improve prediction.
The latest research, published Tuesday in the journal Lancet, tracked for at least a year 102 unconscious subjects, assessing them initially by brain scan, bedside examination and a complex diagnostic test to measure impairments of consciousness. All were diagnosed as either minimally conscious, locked in, or unresponsively wakeful (also called vegetative).
Imaging the subjects' brains with a positron emission tomography, or PET, scan allowed researchers to predict accurately 74 percent of the time whether a patient would show evidence of consciousness a year later. It was a better prognosticator of a poor outcome, accurately predicting that a patient would continue to be vegetative or minimally conscious in 92 percent of cases. But in 67 percent of cases in which PET scan results suggested a patient would regain some level of lost consciousness, he or she did so.
PET imaging of 39 healthy control subjects helped researchers sketch the activity profile of a fully functioning brain and of brains with distinct patterns of impairment: Even when no difference in two patients' awareness levels was evident, the metabolic patterns of a brain in a vegetative state looked very different from those of a brain with intermittent consciousness.
Of 41 patients who had been deemed vegetative by existing diagnostic methods, PET scanning detected evidence of minimal but existing consciousness in 13 patients. After a year, nine of those 13 patients had progressed into a minimally conscious state or better, while three had died of complications or because further treatment was withheld. One remained in a vegetative state. None of the remaining 28 patients had regained a measurable degree of conscious awareness.