Cerebral 18F-FDG PET may predict long-term recovery of patients in vegetative states

Cerebral ¹⁸F-FDG PET could be used to complement bedside exams and predict long-term recovery of patients with unresponsive wakefulness syndrome, according to a study published online April 15 by The Lancet.

Detecting unambiguous signs of consciousness in patients with severe brain damage is no easy task. Neuroimaging methods are in development to accompany bedside exams investigating the compatibility of a patient’s cerebral activity with consciousness. ¹⁸F-FDG PET can examine areas of the brain associated with consciousness, thereby enabling visualization of glucose metabolism at the whole brain level.

Lead author Johan Stender, MD, of the University Hospital of Liège in Belgium, and colleagues conducted a validation study of cerebral ¹⁸F-FDG PET and functional MRI (fMRI) to establish the diagnostic and prognostic utility of neuroimaging in patients with unresponsive wakefulness syndrome.

The study included 41 patients diagnosed with unresponsive wakefulness syndrome, four with locked-in syndrome and 81 in a minimally conscious state with traumatic or non-traumatic causes. During mental activation tasks, repeated standardized clinical assessments with the Coma Recovery Scale—Revised (CRS-R), cerebral ¹⁸F-FDG PET and fMRI were performed. The diagnostic accuracy of the two imaging methods with CRS-R diagnosis as a reference was calculated by the researchers. They also assessed outcome after 12 months with the Glasgow Outcome Scale—Extended.

High sensitivity was observed with cerebral ¹⁸F-FDG PET for identification of patients in a minimally conscious state. The modality also had a high congruence of 85 percent with behavioral CRS-R scores.

In comparison, the active fMRI method was less sensitive at diagnosis of a minimally conscious state and had a lower overall congruence with behavioral scores. Cerebral ¹⁸F-FDG PET correctly predicted outcome in 75 of 102 patients, while fMRI was correct in 36 of 65 patients.

Thirteen of the 42 behaviorally unresponsive patients exhibited brain activity compatible with minimal consciousness on at least one neuroimaging test. Nine of 13 patients, or 69 percent, recovered consciousness.

“Neuroimaging diagnosis should not stand alone, but complement standardised behavioural assessments,” wrote Stender and colleagues. “By definition, neuroimaging cannot challenge a certain clinical diagnosis of minimally conscious states. Therefore, we propose that behavioural assessments and neuroimaging could be combined to screen for non-behavioural minimally conscious states, and identify cases with potential for long-term recovery of consciousness.”

The authors assert that fMRI may complement assessment during mental tasks by providing information about preserved cognitive capability, but should not be the primary imaging-based method used.

“Future work should aim to validate other promising neuroimaging-based differential diagnostic markers, such as quantified metabolic markers, resting state fMRI, or electroencephalography with transcranial magnetic stimulation,” they concluded.