18F-FDG/PET Helps Predict Prognosis of Vegetative Patients

Cerebral 18F-fluorodeoxyglucose (FDG) PET can assist in predicting the long-term recovery of patients with unresponsive wakefulness syndrome, according to a study published in The Lancet.

Researchers from Belgium, Canada, and Denmark performed a clinical validation study to test the diagnostic accuracy of functional 18F-FDG PET and functional MRI (fMRI) in clinical practice.

The study comprised 41 patients with unresponsive wakefulness syndrome, four with locked-in syndrome, and 81 who were in a minimally conscious state (MCS), diagnosed by the Coma Recovery Scale-Revised (CRS-R). The patients underwent repeated standardized clinical assessments with the CRS-R, 18F-FDG MRI and fMRI during mental activation tasks. Outcome was assessed after 12 months using the Glasgow Outcome Scale-Extended.

The researchers found that overall, the 18F-FDG PET was better than fMRI in distinguishing conscious from unconscious patients. Mental imagery fMRI was less sensitive at diagnoses of a MCS than 18-F FDG PET (45 percent versus 93 percent), and had less agreement with behavioral CRS-R scores than the PET (63 percent versus 85 percent). In addition, the PET was about 74 percent accurate in predicting the extent of recovery within the next year compared with 56 percent with the fMRI.

“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,” lead author Steven Laureys, PhD, of the University of Liege in Belgium, said in a release.

The PET correctly predicted the outcome in 75 of 102 patients (74 percent) and fMRI did so in 36 of 65 patients (56 percent). In addition, 13 of 42 patients who were behaviorally unresponsive showed brain activity compatible with minimal consciousness on at least one neuroimaging test, and nine of 13 (69 percent) subsequently recovered consciousness.

The researchers concluded that cerebral 18F-FDG PET could be used to complement bedside assessments and fMRI may be useful in differential diagnosis but it is not as accurate as the PET.