The journal of pain : official journal of the American Pain Society
-
Randomized Controlled Trial
Pain relief is associated with improvement in motor function in complex regional pain syndrome type 1: secondary analysis of a placebo-controlled study on the effects of ketamine.
There are indications of motor circuit changes in patients with complex regional pain syndrome (CRPS). Nevertheless, although several studies have analyzed motor behavior in CRPS, a relation with pain could not be detected. This might be explained by the use of cross-sectional designs in these studies, in which pain is considered as a trait- rather than a state-dependent variable. We therefore studied the time-dependent relation between pain and motor function in affected arms of 29 CRPS patients during their participation in a placebo-controlled ketamine study. Movement parameters (velocity, frequency, amplitude, and number of arrests) were assessed during a finger tapping task. Linear mixed model analysis of the effects of pain (numerical rating scale score), treatment (ketamine/placebo), and week (1, 3, 6, and 12 weeks after treatment) on the movement parameters revealed that pain intensity was significantly (inversely) related to motor function, irrespective of whether patients had received ketamine or placebo. Movement parameters changed 3-12% per point numerical rating scale change. Because patients were unaware of possible effects of ketamine on motor function, these findings suggest that motor function changes were mediated by, or occurred simultaneously with, changes in pain intensity. By improving motor function, pain relief may offer a window of opportunity for rehabilitation programs in CRPS. ⋯ This article provides evidence for a direct relation between pain and motor function in CRPS, which indicates that pain relief may be an important factor in the treatment of motor disturbances in this condition. These findings may help to advance our understanding of the pathways underlying motor disturbances in CRPS.
-
Vicarious pain has been shown to enhance observers' nociceptive reactivity and pain perception. We exposed healthy participants to specific parts of facial pain expressions in order to investigate which components are required to induce this modulation. We created 2 classes of stimuli: one containing the most useful information for identification of pain expressions (diagnostic) and one containing the least useful information (antidiagnostic). Twenty-eight normal volunteers received electrical stimulation of the sural nerve immediately after they viewed these stimuli. Subjective ratings (intensity and unpleasantness) as well as the nociceptive flexion reflex (NFR) evoked by the shock were recorded. Results show that diagnostic stimuli lead to higher subjective ratings of shock pain than the antidiagnostic stimuli, but the stimuli classes had no significant impact on the NFR. A control experiment showed that our facial stimuli were given very low valence and arousal ratings compared to stimuli previously used to demonstrate the effect of emotional pictures on pain. Thus, the results are unlikely to be explained by emotions felt by the observer and suggest a vicarious facilitation of supraspinal pain processing induced by key features underlying pain expressions recognition. Results provide further support to the perception-action model of empathy. ⋯ This study demonstrates that visual features that are efficiently used for the recognition of pain expressions are sufficient to induce a vicarious facilitation of self-pain. Supraspinal pain responses were modulated by the informativeness of the areas of the pain expressions that participants viewed prior to the painful stimulations.
-
Review Meta Analysis
Primary motor cortex function in complex regional pain syndrome: a systematic review and meta-analysis.
Dysfunction in the central nervous system is thought to underlie the movement disorders that commonly occur in complex regional pain syndrome (CRPS), with much of the literature focusing on reorganization of the primary motor cortex (M1). Presumed changes in the M1 representation of the CRPS-affected body part have contributed to new CRPS treatments, which are increasingly being integrated in the clinic. We systematically investigated the evidence for altered M1 function in CRPS. We adhered to rigorous systematic review procedure in our search strategy, risk-of-bias appraisal, and data extraction. Eighteen studies comprising 14 unique data sets were included. The included studies used several neuroimaging techniques, whose outcomes we grouped into M1 cortical excitability, spatial representation, reactivity, and glucose metabolism, and conducted meta-analyses where possible. Risk of bias across studies was high, mainly due to missing data and unblinded assessment of outcomes. No definitive conclusions can be drawn regarding M1 spatial representation, reactivity, or glucose metabolism in CRPS. There is limited evidence for bilateral M1 disinhibition in CRPS of the upper limb. ⋯ Despite widely held assumptions of primary motor cortex dysfunction in complex regional pain syndrome, there is only evidence to support bilateral disinhibition, and there is high risk of bias across the literature.
-
Randomized Controlled Trial
An explanatory study evaluating the muscle relaxant effects of intramuscular magnesium sulphate for dystonia in complex regional pain syndrome.
The treatment of dystonia related to complex regional pain syndrome (CRPS) remains unsatisfactory, raising the need of alternative targets for intervention. In dystonia, pathologic muscle changes may occur, which contributes to stiffness. Because magnesium sulphate may act as a muscle relaxant through its actions on the neuromuscular junction and muscle, we performed an explanatory study of the muscle relaxant effect and safety of intramuscular magnesium sulphate (IMMG) in CRPS patients with dystonia. In a double-blind randomized placebo-controlled crossover study, 30 patients were assigned to 3-week treatments of IMMG and placebo. Treatments were separated by a 1-week washout period. The daily dose of IMMG was 1,000 mg in week 1, 1,500 mg in week 2, and 2,000 mg in week 3. The primary outcome measure was the difference in change in Burke-Fahn-Marsden scores after 3 weeks of treatment between both interventions. Secondary outcomes involved severity of dystonia, myoclonus, tremor, and pain, and functional activity. Data of 22 patients available for the explanatory analysis revealed no significant differences between IMMG and placebo treatment in any of the outcomes. In conclusion, we found no indication of efficacy of IMMG in a daily dose of 2,000 mg as a muscle relaxant in CRPS-related dystonia. ⋯ In this double-blind placebo-controlled crossover study there was no evidence found of a muscle relaxant effect of intramuscular magnesium sulphate in dystonia related to CRPS. Consequently, there is insufficient support for new studies evaluating the efficacy of other routes of MG administration in CRPS-related dystonia.
-
Pain is ultimately a perceptual phenomenon. It is built from information gathered by specialized pain receptors in tissue, modified by spinal and supraspinal mechanisms, and integrated into a discrete sensory experience with an emotional valence in the brain. Because of this, studying intact animals allows the multidimensional nature of pain to be examined. A number of animal models have been developed, reflecting observations that pain phenotypes are mediated by distinct mechanisms. Animal models of pain are designed to mimic distinct clinical diseases to better evaluate underlying mechanisms and potential treatments. Outcome measures are designed to measure multiple parts of the pain experience, including reflexive hyperalgesia measures, sensory and affective dimensions of pain, and impact of pain on function and quality of life. In this review, we discuss the common methods used for inducing each of the pain phenotypes related to clinical pain syndromes as well as the main behavioral tests for assessing pain in each model. ⋯ Understanding animal models and outcome measures in animals will assist in translating data from basic science to the clinic.