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Background and Objectives Somatic antinociceptive effects of baclofen have been demonstrated in animal models. We hypothesized that if enhanced thermal or pain sensitivity is produced by loss of gamma-aminobutyric acid ( GABA)-ergic tone in the central nervous system, spinal administration of GABA agonists might be predicted to be effective in thermal and/or pain perception changes and pain-related evoked potentials in candidates for intrathecal baclofen ( ITB) treatment. Methods Eleven patients with severe spinal cord injury ( SCI) who suffered from severe spasticity were evaluated during a 50-μg ITB bolus test. Warm and heat pain thresholds, evoked heat pain perception, and contact heat-evoked potentials ( CHEPs) were determined above SCI level from the right and left sides. Nine age- and gender-matched healthy volunteers undergoing repeat testing without any placebo injection served as control group. Result In patients, heat pain perception threshold increased, and evoked pain perception and amplitude of CHEPs decreased significantly after ITB bolus application in comparison with baseline ( p < 0.005), with no change in warm perception threshold. In controls, no significant changes were observed in repeat testing over time. Conclusion Our findings indicate that ITB modulates heat pain perception threshold, evoked heat pain perception and heat pain-related evoked potentials without inducing warm perception threshold changes in SCI patients. This phenomenon should be taken into account in the clinical evaluation and management of pain in patients receiving baclofen. [ABSTRACT FROM AUTHOR]

Background Neuropathic pain ( NP) is common in spinal cord injury ( SCI) patients. One of its manifestations is a lowering of pain perception threshold in quantitative thermal testing ( QTT) in dermatomes rostral to the injury level. Transcranial direct current stimulation ( tDCS) combined with visual illusion ( VI) improves pain in SCI patients. We studied whether pain relief with tDCS + VI intervention is accompanied by a change in contact heat- evoked potentials ( CHEPs) or in QTT. Methods We examined 18 patients with SCI and NP before and after 2 weeks of daily tDCS + VI intervention. Twenty SCI patients without NP and 14 healthy subjects served as controls. We assessed NP intensity using a numerical rating scale ( NRS) and determined heat and pain thresholds with thermal probes. CHEPs were recorded to stimuli applied at C4 level, and subjects rated their perception of evoked pain using NRS during CHEPs. Results Thirteen patients reported a mean decrease of 50% in the NRS for NP after tDCS + VI. Evoked pain perception was significantly higher than in the other two groups, and reduced significantly together with CHEPs amplitude after tDCS + VI with respect to baseline. Pain perception threshold was significantly lower than in the other two groups before tDCS + VI intervention, and increased significantly afterwards. Conclusion Two weeks of tDCS + VI induced significant changes in CHEPs, evoked pain and heat pain threshold in SCI patients with NP. These neurophysiological tests might be objective biomarkers of treatment effects for NP in patients with SCI. [ABSTRACT FROM AUTHOR]

The cutaneous silent period (CSP) is a spinal inhibitory reflex mediated by Aδ fibres. The postinhibitory rebound of electromyographic (EMG) activity following the CSP has been mainly attributed to resynchronization of motoneurons, but the possibility of startle reflex activity contributing to the EMG burst has also been suggested. Several types of reflexes may be suppressed by a preceding weak stimulus – a phenomenon called prepulse inhibition (PPI). Our aim was to study whether PPI would diminish the EMG rebound, thereby providing further evidence for excitatory reflex activity contained within the postinhibitory EMG rebound following the CSP. Ten healthy subjects underwent CSP testing following noxious digit II stimulation in two conditions, with and without a prepulse applied to digit III. Rectified surface EMG recordings were obtained from right orbicularis oculi, sternocleidomastoid and thenar muscles of the dominant hand during thumb abduction with 25% of maximum force. The area of the EMG rebound and the EMG reflex responses in orbicularis oculi and sternocleidomastoid were significantly smaller in recordings where a prepulse stimulus was applied 100 ms before the stimulus as compared to control responses without prepulse. CSP onset and end latency, CSP duration, and the degree of EMG suppression were not influenced. Prepulses significantly reduced subjective discomfort as based on visual analog scale scores. Inhibition of the EMG rebound by prepulse stimulation supports the hypothesis that the excitatory EMG activity following the CSP contains not only resynchronization of motoneuronal firing, but also an excitatory reflex component. The most probable type of reflex seems to be a somatosensory startle reflex, a defence reaction which is generated in structures located in the caudal brainstem following an unexpected intense stimulus. Reduction of the discomfort associated with high-intensity electrical fingertip stimulation by a prepulse without affecting CSP parameters underlines the utility of PPI in the context of CSP testing. [ABSTRACT FROM AUTHOR]