1. ¹⁸F-FDG PET reliably predicted which vegetative patients had the potential to regain consciousness.
2. ¹⁸F-FDG PET had high sensitivity and agreement with clinical behavioral assessments in detecting the degree of consciousness in patients compared to fMRI.
Evidence Rating Level: 2 (Good)
Study Rundown: Disorders of consciousness are characterized into various pathological states. These include unresponsive wakefulness syndrome (UWS), or a vegetative state, in which patients are arousable but have no awareness; locked-in syndrome, in which patients are fully conscious but physically unresponsive; or a minimally conscious state (MCS), in which patients can respond to some stimuli and show fluctuating awareness. While correct diagnoses often have important ethical and therapeutic implications, traditional clinical bedside examinations can have significant misdiagnosis rates. This study included 41 patients with UWS, 4 with locked-in syndrome, and 81 in a MCS to assess whether ¹⁸F-fluorodeoxyglucose (FDG) PET and functional MRI (fMRI) could be used to detect cerebral activity along with standardized clinical assessment using the Coma Recovery Scale-Revised (CRS-R). ¹⁸F-FDG PET was found to have a higher sensitivity for identifying patients in a MCS and higher agreement with CRS-R scores than fMRI. ¹⁸F-FDG PET also correctly predicted outcomes in a higher percentage of patients than fMRI. This study was limited by the small sample size, as well as a lack of a true gold standard neurological assessment to compare the imaging results. Nevertheless, the results show that ¹⁸F-FDG PET may have prognostic values in patients with disorders of the consciousness.
Funding: The Belgian National Funds for Scientific Research (FNRS), Fonds Léon Fredericq, the European Commission, the James McDonnell Foundation, the Mind Science Foundation, the French Speaking Community Concerted Research Action, the University of Copenhagen, and the University of Liège.
Relevant Reading: Bedside detection of awareness in the vegetative state: a cohort study
In-Depth [retrospective cohort]: 126 patients (mean age 41, SD 18 years, 75 men) included in the study were diagnosed with having unresponsive wakefulness syndrome (n=41), locked-in syndrome (n=4), or a minimally conscious state (n=81) using CRS-R assessments. For ¹⁸F-FDG PET scans, patients were compared to 39 healthy, paid volunteers with no history of neurological disorders. For fMRI, patients were asked to do mental tasks during scanning and results were compared to 16 healthy, paid volunteers with no history of neurological disorders. Only 112 of 122 (92%) patients were assessed with ¹⁸F-FDG PET and 70 of 122 (59%) with fMRI due to technical reasons. Outcome data was available for 102 of 112 patients with ¹⁸F-FDG PET scans and 65 of 70 patients with fMRI scans.
¹⁸F-FDG PET had a high sensitivity for identifying patients in a MCS (93%, 95% Confidence Interval [CI] 85–98%) and high agreement with CRS-R scores (85%, 95% CI 77–90%). fMRI method was less sensitive at diagnosis of a MCS (45%, 95% CI 30–61%) and had lower agreement with CRS-R scores (63%, 95% CI 51–73%). ¹⁸F-FDG PET correctly predicted outcome in 75 of 102 patients (74%, 95% CI 64–81%), and fMRI in 36 of 65 patients (56%, 95% CI 43–67%).
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