According to new research from Liège, Belgium and published in The Lancet ( Stender J et al Diagnostic precision of PET imaging and functional MRI The Lancet April 16th 2014) functional brain imaging using PET is a promising tool for determining which severely brain damaged individuals in vegetative states have the potential to recover consciousness
In severely brain-damaged individuals, judging the level of consciousness is challenging. Traditionally, bedside clinical examinations have been used to decide whether patients are in a minimally conscious state (MCS), in which there is some evidence of awareness and response to stimuli, or are in a vegetative state (VS), where there is neither, and the chance of recovery is much lower. But up to 40% of patients are misdiagnosed using these examinations.
The new study assessed whether two functional brain imaging techniques— FDG-PET and fMRI could distinguish between vegetative and MCS in 126 patients with severe brain injury (81 in a MCS, 41 in a VS, and four with locked-in syndrome—a behaviorally unresponsive but conscious control group) who had been referred to the University Hospital of Liége, from across Europe. The researchers then compared their results with the well-established standardised Coma Recovery Scale–Revised (CSR-R) behavioral test, which is considered the most validated and sensitive method for discriminating very low awareness.
Overall, FDG-PET was better than fMRI in distinguishing conscious from unconscious patients. Mental imagery fMRI was less sensitive at diagnosis of a MCS than FDG-PET, and had less agreement with behavioral CRS-R scores than FDG-PET. Likewise, FDG-PET was about 74% accurate in predicting the extent of recovery within the next year, compared with 56% for fMRI.
Importantly, a third of the 36 patients diagnosed as behaviorally unresponsive on the CSR-R test who were scanned with FDG-PET showed brain activity consistent with the presence of some consciousness. Nine patients in this group subsequently recovered a reasonable level of consciousness.
“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”, says study leader Professor Steven Laureys.
Commenting on the study, Jamie Sleigh and Catherine Warnaby add, “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. 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 practise without it.”