Sympathetic Blocks as a Predictor for Response to Ketamine Infusion in Patients with Complex Regional Pain Syndrome: A Multicenter Study

BACKGROUND

Ketamine infusions are frequently employed for refractory complex regional pain syndrome (CRPS), but there are limited data on factors associated with treatment response. Sympathetic blocks are also commonly employed in CRPS for diagnostic and therapeutic purposes and generally precede ketamine infusions.

OBJECTIVES

We sought to determine whether demographic and clinical factors, and technical and psychophysical characteristics of sympathetic blocks are associated with response to ketamine infusion.

METHODS

In this multi-center retrospective study, 71 patients who underwent sympathetic blocks followed by ketamine infusions at 4 hospitals were evaluated. Sympathetically maintained pain (SMP) was defined as ≥ 50% immediate pain relief after sympathetic block and a positive response to ketamine was defined as ≥ 30% pain relief lasting over 3 weeks.

RESULTS

Factors associated with a positive response to ketamine in univariable analysis were the presence of SMP (61.0% success rate vs 26.7% in those with sympathetically independent pain; P = .009) and post-block temperature increase (5.66 ± 4.20 in ketamine responders vs 3.68 ± 3.85 in non-responders; P = .043). No psychiatric factor was associated with ketamine response. In multivariable analysis, SMP (OR 6.54 [95% CI 1.83, 23.44]) and obesity (OR 8.75 [95% 1.45, 52.73]) were associated with a positive ketamine infusion outcome.

CONCLUSIONS

The response to sympathetic blocks may predict response to ketamine infusion in CRPS patients, with alleviation of the affective component of pain and predilection to a positive placebo effect being possible explanations.

Managing Chronic Neuropathic Pain: Recent Advances and New Challenges

Aim. Neuropathic pain affects 7–10% of the population, with most of the patients receiving inadequate and incomplete treatment. Owing to the high financial burden and the poor quality of life of the patients and their caretakers, there is a dire need to address the challenges in diagnosing and treating chronic neuropathic pain. Methods. This literature review was conducted to review novel treatments and related challenges through a systematic search from sources such as PubMed, Google Scholar with the combination of MESH words such as neuropathic pain, management of neuropathic pain. Articles from non-English literature, reports without human subjects, animal studies, and abstracts/posters were excluded. However, human studies and studies published in English were included. Result. This review article discusses novel treatment modalities while acknowledging the challenges medical workers face while encountering neuropathic pain. Despite the recent advances in diagnosis and treatment modalities, several challenges still exist. Hence, there is still a need to explore the various treatment modalities, emphasizing the cause and underlying pathophysiology of neuropathic pain. Conclusion. We recommend integrated multimodal treatment with the current treatment facility, including various medical disciplines. However, a personalized approach would work the best depending on the ’patient’s medical history. Therefore, this article recommends an integrated, cause-specific, cost-effective approach to address this problem of chronic neuropathic pain.

Efficacy of the lumbar sympathetic ganglion block in lower limb pain and its application prospects during the perioperative period

The sympathetic nervous system is involved in the physiological pathogenesis of many different types of chronic pain. Sympathetic blocks can interrupt the reflex control system by intercepting the noxious afferent fibers accompanying autonomic nerves, resulting in changes in peripheral or central sensory processing. A lumbar sympathetic ganglion block (LSGB), as a treatment method, refers to the injection of nerve blockers into the corresponding lumbar sympathetic nerve segments, usually requiring imaging assistance (CT, X-ray, ultrasound) to guide. At present, LSGB has been widely used in the clinical treatment of lower limb pain, such as neuropathic pain, lower limb ischemic pain, and so on. Its mechanism of action may be through inhibiting sympathetic nerve activity and dilating blood vessels, thereby alleviating pain and inhibiting stress response. However, there are few reports of LSGB during the perioperative period, especially in postoperative pain and gastrointestinal function. Therefore, by studying the literature about LSGB-related studies, this article reviews the anatomy of the lumbar sympathetic nerve (LSN), with its clinical application and possible mechanism. We reviewed the analgesic effect of LSGB in patients with lower limb pain and postoperative pain and the potential application prospects in the recovery of gastrointestinal function, finally providing a reference for its clinical application.

Neuropathic Pain in the Elderly

Neuropathic pain due to a lesion or a disease of the somatosensory system often affects older people presenting several comorbidities. Moreover, elderly patients are often poly-medicated, hospitalized and treated in a nursing home with a growing risk of drug interaction and recurrent hospitalization. Neuropathic pain in the elderly has to be managed by a multidimensional approach that involves several medical, social and psychological professionals in order to improve the quality of life of the patients and, where present, their relatives.

Residual limb pain: An evidence-based review

Acquired limb loss, whether from accident or amputation, occurs with an incidence of greater than 175,000 per year in the United States. Current prevalence is estimated at greater than 1.5 million and is expected to double within 30 years. While many patients with amputations may have no significant pain or sensory issues after healing from the initial loss, one-quarter to one-half of patients may have ongoing difficulties with residual limb pain, phantom limb pain, or phantom limb sensation. This review explores the potential etiologies of those symptoms, as well as a variety of treatment options that a practitioner may consider when approaching this condition.

The role of afferent input in postamputation pain: a randomized, double-blind, placebo-controlled crossover study

In this randomized, double-blind, placebo-controlled crossover study, we investigated whether a peripheral nerve block could temporarily eliminate phantom and stump pain after amputation. Amputees with constant postamputation pain were included and randomized to receive a nerve block with lidocaine 2% with adrenaline or saline in a crossover design. Spontaneous phantom and stump pain and evoked responses were assessed at baseline and at fixed time-points until 120 minutes after lidocaine or saline injection. The primary outcome was the difference in absolute change between worst pain intensity, either phantom or stump pain, at baseline and at 30 minutes after lidocaine or saline injection. Twelve amputees were randomized and 9 patients were included in the analysis. The absolute change in median worst pain intensity between lidocaine and saline injection was -2.0 (interquartile range, -4.0 to 0.0) (n = 9, P = 0.12). Nine of 9 patients reported at least some pain relief after lidocaine injection compared with only 2 of 9 patients after saline injection (P = 0.02). Phantom pain intensity was significantly reduced after lidocaine compared with saline injection (P = 0.04), whereas there was no significant change in stump pain intensity between the 2 interventions (P = 0.17). In all 9 amputees, evoked responses were eliminated after lidocaine injection. Thus, our findings suggest that afferent input from the peripheral nervous system plays an important role in postamputation pain.