Perception of pain in the minimally conscious state with PET activation: an observational study.
BACKGROUND
Patients in a minimally conscious state (MCS) show restricted self or environment awareness but are unable to communicate consistently and reliably. Therefore, better understanding of cerebral noxious processing in these patients is of clinical, therapeutic, and ethical relevance.


METHODS
We studied brain activation induced by bilateral electrical stimulation of the median nerve in five patients in MCS (aged 18-74 years) compared with 15 controls (19-64 years) and 15 patients (19-75 years) in a persistent vegetative state (PVS) with (15)O-radiolabelled water PET. By way of psychophysiological interaction analysis, we also investigated the functional connectivity of the primary somatosensory cortex (S1) in patients and controls. Patients in MCS were scanned 57 (SD 33) days after admission, and patients in PVS 36 (9) days after admission. Stimulation intensities were 8.6 (SD 6.7) mA in patients in MCS, 7.4 (5.9) mA in controls, and 14.2 (8.7) mA in patients in PVS. Significant results were thresholded at p values of less than 0.05 and corrected for multiple comparisons.


RESULTS
In patients in MCS and in controls, noxious stimulation activated the thalamus, S1, and the secondary somatosensory or insular, frontoparietal, and anterior cingulate cortices (known as the pain matrix). No area was less activated in the patients in MCS than in the controls. All areas of the cortical pain matrix showed greater activation in patients in MCS than in those in PVS. Finally, in contrast with patients in PVS, those in MCS had preserved functional connectivity between S1 and a widespread cortical network that includes the frontoparietal associative cortices.


CONCLUSIONS
Cerebral correlates of pain processing are found in a similar network in controls and patients in MCS but are much more widespread than in patients in PVS. These findings might be objective evidence of a potential pain perception capacity in patients in MCS, which supports the idea that these patients need analgesic treatment.
Coma Science Group, Cyclotron Research Center, University of Liège, Belgium.
Mélanie
M
Boly
Marie-Elisabeth
ME
Faymonville
Caroline
C
Schnakers
Philippe
P
Peigneux
Bernard
B
Lambermont
Christophe
C
Phillips
Patrizio
P
Lancellotti
Andre
A
Luxen
Maurice
M
Lamy
Gustave
G
Moonen
Pierre
P
Maquet
Steven
S
Laureys
D000293:Adolescent; D000328:Adult; D000368:Aged; D000700:Analgesics / Q000592:standards / Q000627:therapeutic use; D001921:Brain / Q000000981:diagnostic imaging / Q000503:physiopathology; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D003243:Consciousness / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D006179:Gyrus Cinguli / Q000502:physiology; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D009415:Nerve Net / Q000000981:diagnostic imaging / Q000503:physiopathology; D010146:Pain / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D018458:Persistent Vegetative State / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D049268:Positron-Emission Tomography / Q000379:methods*; D013003:Somatosensory Cortex / Q000502:physiology; D013788:Thalamus / Q000502:physiology
D000700:Analgesics