Cortical Responsiveness to Nociceptive Stimuli in Patients with Chronic Disorders of Consciousness: Do C-Fiber Laser Evoked Potentials Have a Role?

Antonino Naro,Margherita Russo,Antonino Leo,Patrizia Pollicino,Carmela Rifici,Rocco Salvatore Calabrò,Placido Bramanti,Lawrence M Ward

doi:10.1371/journal.pone.0144713

Antonino Naro, Margherita Russo + Show 6 more

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https://doi.org/10.1371/journal.pone.0144713

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Journal: PloS one	Publication Date: Dec 16, 2015
Citations: 14	License type: CC BY 4.0

Affiliation: Centro Neurolesi Bonino Pulejo

Abstract

It has been shown that the presence of Aδ-fiber laser evoked potentials (Aδ-LEP) in patients suffering from chronic disorders of consciousness (DOC), such as vegetative state (VS) and minimally conscious state (MCS), may be the expression of a residual cortical pain arousal. Interestingly, the study of C-fiber LEP (C-LEP) could be useful in the assessment of cortical pain arousal in the DOC individuals who lack of Aδ-LEP. To this end, we enrolled 38 DOC patients following post-anoxic or post-traumatic brain injury, who met the international criteria for VS and MCS diagnosis. Each subject was clinically evaluated, through the coma recovery scale-revised (CRS-R) and the nociceptive coma scale-revised (NCS-R), and electrophysiologically tested by means of a solid-state laser for Aδ-LEP and C-LEP. VS individuals showed increased latencies and reduced amplitudes of both the Aδ-LEP and C-LEP components in comparison to MCS patients. Although nearly all of the patients had both the LEP components, some VS individuals showed only the C-LEP ones. Notably, such patients had a similar NCS-R score to those having both the LEP components. Hence, we could hypothesize that C-LEP generators may be rearranged or partially spared in order to still guarantee cortical pain arousal when Aδ-LEP generators are damaged. Therefore, the residual presence of C-LEP should be assessed when Aδ-LEP are missing, since a potential pain experience should be still present in some patients, so to properly initiate, or adapt, the most appropriate pain treatment.

Highlights

In contrast to comatose patients, who lack of both wakefulness and awareness, individuals suffering from Vegetative State (VS) are awake but unaware of the environment and cannot purposefully respond to stimuli, whilst patients affected by Minimally Conscious State (MCS) are awake but limitedly aware and may show some purposeful behaviors [1,2]
The N1P1 complex reflects an early stage of sensory processing at unaware level, whereas the N2P2 wave is related to the stimulus saliency, independently from the nociceptive nature of the incoming stimulus [8,10,11,12]
Our findings agree with previous reports showing an increased latency of Aδ-fiber laser evoked potentials (Aδ-Laser evoked potentials (LEP)) in disorder of consciousness (DOC) patients without any significant amplitude inter-group difference [10,11]

Summary

Introduction

In contrast to comatose patients, who lack of both wakefulness and awareness, individuals suffering from Vegetative State (VS) are awake but unaware of the environment and cannot purposefully respond to stimuli, whilst patients affected by Minimally Conscious State (MCS) are awake but limitedly aware and may show some purposeful behaviors [1,2].PLOS ONE | DOI:10.1371/journal.pone.0144713 December 16, 2015CLEP in DOC DiagnosisPain perception in chronic disorder of consciousness (DOC) represents a controversial issue, since there is growing evidence concerning the presence of residual pain experience even in some VS individuals [3,4,5,6]. Taking into account that such patients have a strongly limited repertoire of communication, and that the inability to communicate could not exclude a possible pain experience, the issues of nociception and pain in such individuals are of ethic and clinical importance, especially concerning a proper diagnosis and an adequate pain treatment. Laser evoked potentials (LEP) are extensively used in pain study, since the laser stimulation can selectively activate the nociceptive pathways [7]. Laser stimulation typically evokes several LEP components, reflecting the activity of multiple cortical assemblies within different cortical areas (including primary and secondary somatosensory cortices, insula, and anterior cingulate cortex) that process either nociceptive or non-nociceptive inputs [8,9]. The N1P1 complex reflects an early stage of sensory processing at unaware level, whereas the N2P2 wave is related to the stimulus saliency, independently from the nociceptive nature of the incoming stimulus [8,10,11,12]

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