Background: Making an accurate diagnosis in patients with disorders of consciousness remains challenging. 18F-fluorodeoxyglucose (FDG)-PET has been validated as a diagnostic tool in this population, and allows identifying unresponsive patients with a capacity for consciousness. In parallel, the perturbational complexity index (PCI), a new measure based on the analysis of the electroencephalographic response to transcranial magnetic stimulation, has also been suggested as a tool to distinguish between unconscious and conscious states. The aim of the study was to cross-validate FDG-PET and PCI, and to identify signs of consciousness in otherwise unresponsive patients.
Methods: We jointly applied the Coma Recovery Scale-Revised, FDG-PET and PCI to assess 24 patients with non-acute disorders of consciousness or locked-in syndrome (13 male; 19-54 years old; 12 traumatic; 9 unresponsive wakefulness syndrome, 11 minimally conscious state; 2 emergence from the minimally conscious state, and 2 locked-in syndrome).
Results: FDG-PET and PCI provided congruent results in 22 patients, regardless of their behavioural diagnosis. Notably, FDG-PET and PCI revealed preserved metabolic rates and high complexity levels in four patients who were behaviourally unresponsive.
Conclusion: We propose that jointly measuring the metabolic activity and the electrophysiological complexity of cortical circuits is a useful complement to the diagnosis and stratification of patients with disorders of consciousness.
Keywords: Brain injury; CRS-R, Coma Recovery Scale-Revised; DOC, disorders of consciousness; Disorders of consciousness; EMCS, emergence from the minimally conscious state; Electroencephalography; FDG, 18F-fluorodeoxyglucose; LIS, locked-in syndrome; MCS*, non-behavioural minimally conscious state; MCS, minimally conscious state; PCI, perturbational complexity index; Positron emission tomography; SPM, statistical parametric mapping; TMS–EEG, transcranial magnetic stimulation coupled with high-density EEG; Transcranial magnetic stimulation; UWS, unresponsive wakefulness syndrome; Unresponsive wakefulness syndrome minimally conscious state; fMRI, functional MRI.