A "functional brain imaging technique" could help predict whether or not a comatose patient will wake up.
The technique, known as positron emission tomography (PET), was tested on its ability to asses the potential for a patient in a vegetative state to recover consciousness for the first time, a Lancet news release reported.
"Our findings suggest that PET imaging can reveal cognitive processes that aren't visible through traditional bedside tests, and could substantially complement standard [behavioral] assessments to identify unresponsive or 'vegetative' patients who have the potential for long-term recovery," study leader Professor Steven Laureys of the University of Liége in Belgium, said in the news release.
In the past, judging the brain function of severely brain-damaged individuals has been difficult. Clinical assessments are the norm for determining if a patient is in a minimally conscious state (MCS) in which they respond to some stimuli or are in a vegetative state (VS) in which they are unresponsive and unlikely to recover. About 40 percent of patients are misdiagnosed in these exams.
"In patients with substantial cerebral oedema [swelling of the brain], prediction of outcome on the basis of standard clinical examination and structural brain imaging is probably little better than flipping a coin," Jamie Sleigh of the University of Auckland, New Zealand, and Catherine Warnaby from the University of Oxford, UK, wrote in a linked Comment, the news release reported.
The researchers looked at if "PET with the imaging agent fluorodeoxyglucose (FDG) and functional MRI (fMRI)" would be useful in making those diagnoses. The team tried out the techniques on 126 patients with severe brain injury.
The team determined FDG-PET was better than fMRI in distinguishing between conscious and unconscious patients.
"FDG-PET was about 74 [percent] accurate in predicting the extent of recovery within the next year, compared with 56 [percent] for fMRI," the news release reported.
One third of the 36 patients diagnosed as behaviorally unresponsive were found to have brain activity through the FDG-PET exam. Nine of these patients recovered a "reasonable level" of consciousness.
"We confirm that a small but substantial proportion of [behaviorally] unresponsive patients retain brain activity compatible with awareness. Repeated testing with the CRS-R complemented with a cerebral FDG-PET examination provides a simple and reliable diagnostic tool with high sensitivity towards unresponsive but aware patients. fMRI during mental tasks might complement the assessment with information about preserved cognitive capability, but should not be the main or sole diagnostic imaging method," Laureys said.
"From these data, it would be hard to sustain a confident diagnosis of unresponsive wakefulness syndrome solely on [behavioral] grounds, without PET imaging for confirmation...[This] work serves as a signpost for future studies. Functional brain imaging is expensive and technically challenging, but it will almost certainly become cheaper and easier. In the future, we will probably look back in amazement at how we were ever able to [practice] without it," Jamie Sleigh and Catherine Warnaby wrote.
