Fast track — ArticlesPerception of pain in the minimally conscious state with PET activation: an observational study
Introduction
A persistent vegetative state (PVS) is defined by wakefulness without awareness of self or the environment,1 whereas patients in a minimally conscious state (MCS) show some evidence of self and environmental awareness.2 However, the carers of patients who are minimally conscious have difficulties in assessing the patients' level of conscious pain perception through their behaviour. Moreover, there are no guidelines on pain treatment in patients in MCS.3 Noxious stimulation is a routine clinical procedure for the bedside assessment of consciousness in patients who are severely brain damaged. Noxious stimulation is also part of the commonly used coma scales, such as the Glasgow coma scale (GCS),4 the reaction level scale,5 the Innsbruck coma scale,6 the Edinburgh 2 coma scale,7 and the coma recovery scale.8 The study of cerebral processing of noxious stimulation in these patients is also of clinical, therapeutic, and ethical relevance.9 We have previously reported on the cortical responses of patients in PVS to similar noxious somatosensory stimuli by use of 15O-radiolabelled water PET,10 and found that the only areas that significantly responded to noxious stimulation in patients in PVS were the brainstem, contralateral thalamus, and primary somatosensory cortex (S1). Here, we used an identical set-up to study five patients who are in MCS and compared the results with those from patients in PVS and 15 healthy controls.
Section snippets
Participants
Five non-sedated patients in MCS (4 men; mean age 49 [SD 22] years, range 18–74 years), 15 non-sedated patients in PVS (12 men; mean age 48 [17] years, range 19–75 years), and 15 healthy volunteers (8 male; mean age 40 [9] years, range 19–64 years) were studied prospectively. Table 1 shows the demographic data of the patients in MCS. The aetiologies of the patients in PVS were: cardiorespiratory arrest (n=5), diffuse axonal injury (n=3), drugs overdose (n=2), prolonged respiratory insufficiency
Results
In the controls, noxious stimulation resulted in the subjective experience of pain and increased regional cerebral blood flow in several areas, including the thalamus, striatum, contralateral S1, secondary somatosensory or insular cortices, superior temporal, posterior, parietal, posterior cingulate, prefrontal, and anterior cingulate cortices (table 2 and figure). Compared with baseline, deactivations could also be found in the posterior cingulate and precuneus and medial prefrontal cortices (
Discussion
Pain is a subjective experience.23 By definition, patients in MCS are unable to consistently and reliably communicate their experiences, and their behavioural responses to noxious stimulation are often difficult to interpret. Even if some patients in MCS can correctly answer yes or no questions at a level above chance, a question such as, “Are you in pain?” might not elicit a reliable response. The behavioural assessment of motor or autonomic signs (ie, respiratory frequency, heart rate, blood
References (46)
Chronic disorders of consciousness
Lancet
(2006)- et al.
Assessment of coma and impaired consciousness. A practical scale
Lancet
(1974) - et al.
Prediction of non-survival after trauma: Innsbruck Coma Scale
Lancet
(1991) - et al.
The JFK Coma Recovery Scale-Revised: measurement characteristics and diagnostic utility
Arch Phys Med Rehabil
(2004) - et al.
Cortical processing of noxious somatosensory stimuli in the persistent vegetative state
Neuroimage
(2002) - et al.
Monitoring rate of recovery to predict outcome in minimally responsive patients
Arch Phys Med Rehabil
(1991) - et al.
Effect of stimulus intensity on short latency somatosensory evoked potentials
Electroencephalogr Clin Neurophysiol
(1979) Ethical guidelines for pain research in humans. Committee on Ethical Issues of the International Association for the Study of Pain
Pain
(1995)- et al.
Thresholding of statistical maps in functional neuroimaging using the false discovery rate
Neuroimage
(2002) - et al.
Valid conjunction inference with the minimum statistic
Neuroimage
(2005)