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

The sensorimotor theory of pathological pain revisited

Harris (1999) proposed that pain can arise in the absence of tissue damage because changes in the cortical representation of the painful body part lead to incongruences between motor intention and sensory feedback. This idea, subsequently termed the sensorimotor theory of pain, has formed the basis for novel treatments for pathological pain. Here we review the evidence that people with pathological pain have changes to processes contributing to sensorimotor function: motor function, sensory feedback, cognitive representations of the body and its surrounding space, multisensory processing, and sensorimotor integration. Changes to sensorimotor processing are most evident in the form of motor deficits, sensory changes, and body representations distortions, and for Complex Regional Pain Syndrome (CRPS), fibromyalgia, and low back pain. Many sensorimotor changes are related to cortical processing, pain, and other clinical characteristics. However, there is very limited evidence that changes in sensorimotor processing actually lead to pain. We therefore propose that the theory is more appropriate for understanding why pain persists rather than how it arises.

Intravenous Ketamine Infusion for Complex Regional Pain Syndrome: Survey, Consensus, and a Reference Protocol

OBJECTIVE

To find and reach a consensus on the usage of ketamine in the treatment of complex regional pain syndrome and to determine a reference protocol for future studies.

DESIGN

Three hundred fifty-one medical professionals participated in our survey on practice procedures, with 104 respondents providing information on their usage of ketamine for treating the pain associated with complex regional pain syndrome. Respondents answered questions about inpatient treatment, outpatient treatment, children vs adults, safety, and basic demographic information. An expert group then met to reach a consensus for a reference protocol.

RESULTS

There is a difference in how inpatients are treated compared with outpatients, making it necessary to have two different reference protocols. The duration of pain relief varied from one to 10 days to one to six months, with a correlation between the duration of pain relief and total infusion hours per round.

CONCLUSIONS

The consensus reference protocols are made up of nine recommended topics. Reference protocols need to be validated by extensive research before guidelines can be created.

Peripheral Neuropathic Pain and Pain Related to Complex Regional Pain Syndrome with and without Fixed Dystonia - Efficient Therapeutic Approach with Local Anesthetics

Peripheral Neuropathic Pain (PNP) as well as the Complex Regional Pain Syndrome (CRPS), also known as “Reflex Sympathetic Dystrophy”, or “Sudeck Dystrophy”, all of them have a poor prognosis. The numerous therapeutic offers are rarely accompanied by convincing success over a long duration of time. Even worse is the prognosis of a fixed dystonia which may develop in the extremities of PNP or CRPS patients. In literature a few cases are reported in which the often unbearable pain of those patients with or without a disabling dystonia disappeared immediately after the injection of local anesthetics (LAs) into the scars of a preceding trauma. This review evaluates publications concerning the neuropathological characteristics of fixed dystonia in PNP/CRPS patients and the electrophysiological processes of scar neuromas. The results of these evaluations support the understanding of the therapeutic successes and their immediate results reported above by the injection of LAs into triggering scars. Therapeutic options are discussed.

The Effect of Ketamine Infusion in the Treatment of Complex Regional Pain Syndrome: a Systemic Review and Meta-analysis

PURPOSE OF REVIEW

Complex regional pain syndrome (CRPS) is a painful debilitating neurological condition that accounts for approximately 1.2% of adult chronic pain population. Ketamine, an NMDA receptor antagonist, is an anesthetic agent that has been used by some pain specialists for CRPS. There is a growing body of clinical evidence to support the use of ketamine in the treatment of neuropathic pain, especially CRPS. This meta-analysis study was aimed to examine the efficacy of ketamine in the treatment of CRPS.

RECENT FINDINGS

A search of Embase, Pubmed, Web of Knowledge, Cochrane, Clinical Trial.gov , and FDA.gov between Jan 1, 1950, and August 1, 2017, was conducted to evaluate ketamine infusion therapy in the treatment of CRPS. We selected randomized clinical trials or cohort studies for meta-analyses. I 2 index estimates were calculated to test for variability and heterogeneity across the included studies. The primary outcome is pain relief. The effect of ketamine treatment for complex regional pain syndrome was assessed by 0-10 scale numerical rating pain score. The secondary outcome is the pain relief event rate, which is defined as the percentage of participants who achieved 30% or higher pain relief in each of the qualified studies. Our meta-analysis results showed that the Ketamine treatment led to a decreased mean of pain score in comparison to the self-controlled baseline (p < 0.000001). However, there is a statistical significance of between-study heterogeneity. The immediate pain relief event rate was 69% (95% confidence interval (CI) 53%, 84%). The pain relief event rate at the 1-3 months follow-ups was 58% (95% CI 41%, 75%). The current available studies regarding ketamine infusion for CRPS were reviewed, and meta-analyses were conducted to evaluate the efficacy of ketamine infusion in the treatment of CRPS. Our findings suggested that ketamine infusion can provide clinically effective pain relief in short term for less than 3 months. However, because of the high heterogeneity of the included studies and publication bias, additional random controlled trials and standardized multicenter studies are needed to confirm this conclusion. Furthermore, studies are needed to prove long-term efficacy of ketamine infusion in the treatment of CRPS.

Differential Efficacy of Ketamine in the Acute versus Chronic Stages of Complex Regional Pain Syndrome in Mice

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful, disabling, and often chronic condition, where many patients transition from an acute phase with prominent peripheral neurogenic inflammation to a chronic phase with evident central nervous system changes. Ketamine is a centrally acting agent believed to work through blockade of N-methyl-D- aspartate receptors and is being increasingly used for the treatment of refractory CRPS, although the basis for the drug's effects and efficacy at different stages of the syndrome remains unclear.

METHODS

The authors used a mouse model of CRPS (n = 8 to 12/group) involving tibia fracture/cast immobilization to test the efficacy of ketamine (2 mg kg day; 7 days) or vehicle infusion during acute (3 weeks after fracture) and chronic (7 weeks after fracture) stages.

RESULTS

Acute-phase fracture mice displayed increased limb temperature, edema, and nociceptive sensitization that were not reduced by ketamine. Fracture mice treated with ketamine during the chronic phase showed reduced nociceptive sensitization that persisted beyond completion of the infusion. During this chronic phase, ketamine also reduced latent nociceptive sensitization and improved motor function at 18 weeks after fracture. No side effects of the infusions were identified. These behavioral changes were associated with altered spinal astrocyte activation and expression of pain-related proteins including N-methyl-D-aspartate receptor 2b, Ca/calmodulin-dependent protein kinase II, and brain-derived neurotrophic factor.

CONCLUSIONS

Collectively, these results demonstrate that ketamine is efficacious in the chronic, but not acute, stage of CRPS, suggesting that the centrally acting drug is relatively ineffective in early CRPS when peripheral mechanisms are more critical for supporting nociceptive sensitization.

Complex regional pain syndrome-significant progress in understanding

Research into complex regional pain syndrome (CRPS) has made significant progress. First, there was the implementation of the official IASP "Budapest" diagnostic criteria. It would be desirable to also define exclusion and outcome criteria that should be reported in studies. The next step was to recognize the complex pathophysiology. After trauma, some inflammation is physiological; in acute CRPS, this inflammation persists for months. There is an abundance of inflammatory and a lack of anti-inflammatory mediators. This proinflammatory network (cytokines and probably also other mediators) sensitizes the peripheral and spinal nociceptive system, it facilitates the release of neuropeptides from nociceptors inducing the visible signs of inflammation, and it stimulates bone cell or fibroblast proliferation, and endothelial dysfunction leading to vascular changes. Trauma may also expose nervous system structures to the immune system and triggers autoantibodies binding to adreno- and acetylcholine receptors. In an individual time frame, the pain in this inflammatory phase pushes the transition into "centralized" CRPS, which is dominated by neuronal plasticity and reorganization. Sensory-motor integration becomes disturbed, leading to a loss of motor function; the body representation is distorted leading to numbness and autonomic disturbances. In an attempt to avoid pain, patients neglect their limb and learn maladaptive nonuse. The final step will be to assess large cohorts and to analyze these data together with data from public resources using a bioinformatics approach. We could then develop diagnostic toolboxes for individual pathophysiology and select focused treatments or develop new ones.

Responsiveness to botulinum toxin type A in muscles of complex regional pain patients with tonic dystonia

Tonic dystonia of the limbs in complex regional pain syndrome (CRPS) is associated with considerable disability. Treatment options are scarce. Botulinum toxin (BoNT) is sometimes used, but the effect is often said to be disappointing. However, this notion stems from case reports and clinicians' opinions but has never been formally studied. We therefore investigated responsiveness to BoNT in CRPS patients with tonic dystonia. We injected the extensor digitorum brevis (EDB) muscle with BoNT-A in 17 patients with CRPS and tonic dystonia to compare the response between affected and unaffected legs. We also investigated the right legs of 17 healthy controls. Responsiveness was defined as a decrease of the amplitude of the compound muscle action potential (CMAP) of >20% from baseline 2 weeks after BoNT-A injection. We controlled for a temperature effect on BoNT efficacy by measuring skin temperature hourly directly above the EDB muscle in the first 2 weeks. CMAP amplitude decreased >20% after injection on the affected side in 16 of 17 CRPS patients, similar to the response in unaffected legs (12/13) or legs of controls (17/17). The degree of CMAP reduction was significantly smaller in patients than in controls (56.0 ± 22.3 vs. 70.6 ± 14.6%; p = 0.031). This may be due to a lower physical activity level and a greater difficulty to localize the EDB muscle properly in affected legs. The decrease in CMAP amplitude was not related to skin temperature. Contrary to the prevailing opinion, BoNT-A has a normal, although perhaps slightly lower efficacy in CRPS patients with dystonia.