Methodological and statistical characteristics of meta-analyses on spinal cord stimulation for chronic pain: a systematic review

BACKGROUND

A growing number of meta-analyses (MA) have investigated the use of spinal cord stimulation (SCS) as a treatment modality for chronic pain. The quality of these MAs has not been assessed by validated appraisal tools.

OBJECTIVE

To examine the methodological characteristics and quality of MAs related to the use of SCS for chronic pain syndromes.

EVIDENCE REVIEW

An online literature search was conducted in Ovid MEDLINE(R), Ovid EMBASE, Ovid Cochrane Database of Systematic Reviews, and Scopus databases (January 1, 2000 through June 30, 2023) to identify MAs that investigated changes in pain intensity, opioid consumption, and/or physical function after SCS for the treatment of chronic pain. MA quality was assessed using A Measurement Tool to Assess Systematic Reviews (AMSTAR-2) critical appraisal tool.

FINDINGS

Twenty-five MAs were appraised in the final analysis. Three were considered "high" quality, three "low" quality, and 19 "critically low" quality, per the AMSTAR-2 criteria. There was no association between the publication year and AMSTAR-2 overall quality (β 0.043; 95% CI -0.008 to 0.095; p=0.097). There was an association between the impact factor and AMSTAR-2 overall quality (β 0.108; 95% CI 0.044 to 0.172; p=0.002), such that studies published in journals with higher impact factors were associated with higher overall quality. There was no association between the effect size and AMSTAR-2 overall quality (β -0.168; 95% CI -0.518 to 0.183; p=0.320).According to our power analysis, three studies were adequately powered (>80%) to reject the null hypothesis, while the remaining studies were underpowered (<80%).

CONCLUSIONS

The study demonstrates a critically low AMSTAR-2 quality for most MAs published on the use of SCS for treating chronic pain. Future MAs should improve study quality by implementing the AMSTAR-2 checklist items.

PROSPERO REGISTRATION NUMBER

CRD42023431155.

The Use of Scrambler Therapy in Treating Chronic Pain Syndromes: A Systematic Review

BACKGROUND

Scrambler therapy (ST) is a noninvasive method of transcutaneous neuromodulation that has 510(K) clearance from the United States Food and Drug Administration for treating acute pain, postoperative pain, and intractable chronic pain. Since its inception, ST has been used to treat many chronic pain syndromes in a variety of patient populations. We synthesized the available literature for ST to delineate its overall evidence basis.

MATERIALS AND METHODS

We performed a systematic review based on conventional Preferred Reporting Items for Systematic Reviews and Meta-Analyses methods by surveying multiple data sources from January 1950 through October 2021. Two review authors, independently and in a standardized, unblinded fashion, conducted a systematic review to identify relevant studies and extract the necessary outcome measures. A conservative search strategy was implemented to identify all ST studies for the treatment of chronic pain syndromes. Primary outcome parameters collected were analgesic benefit, adverse effects, and other metrics such as sensorimotor testing.

RESULTS

A total of 21 studies met the final criteria for study inclusion and comprised randomized controlled trials (n = 8), prospective observational studies (n = 10), and retrospective cohort studies (n = 3). Nearly all the reported studies explored the use of ST for the treatment of neuropathic pain, with chemotherapy-induced peripheral neuropathy being the most studied condition. Most studies were limited by small cohorts but reported ST being safe, well tolerated, and providing clinically meaningful pain reduction. The duration of posttreatment follow-up ranged from ten to 14 days (concordant with completion of typical ST protocols) to three months. Secondary benefits such as medication reduction and improvement of sensory and motor symptoms were noted by some studies.

CONCLUSIONS

ST is regarded as a safe intervention with potential for significant analgesic benefit for neuropathic pain conditions. Although the available evidence is most robust for treating chemotherapy-induced peripheral neuropathy, ST has also been shown to be effective in treating other neuropathic pain syndromes. Evidence for ST use in nociceptive pain conditions is limited but appears promising. The favorable safety profile and increasing evidence basis for ST warrant more extensive recognition and consideration for use in clinical care.

Comprehensive, Evidence-Based, Consensus Guidelines for Prescription of Opioids for Chronic Non-Cancer Pain from the American Society of Interventional Pain Physicians (ASIPP)

BACKGROUND

Opioid prescribing in the United States is decreasing, however, the opioid epidemic is continuing at an uncontrollable rate. Available data show a significant number of opioid deaths, primarily associated with illicit fentanyl use. It is interesting to also note that the data show no clear correlation between opioid prescribing (either number of prescriptions or morphine milligram equivalent [MME] per capita), opioid hospitalizations, and deaths. Furthermore, the data suggest that the 2016 guidelines from the Centers for Disease Control and Prevention (CDC) have resulted in notable problems including increased hospitalizations and mental health disorders due to the lack of appropriate opioid prescribing as well as inaptly rapid tapering or weaning processes. Consequently, when examined in light of other policies and complications caused by COVID-19, a fourth wave of the opioid epidemic has been emerging.

OBJECTIVES

In light of this, we herein seek to provide guidance for the prescription of opioids for the management of chronic non-cancer pain. These clinical practice guidelines are based upon a systematic review of both clinical and epidemiological evidence and have been developed by a panel of multidisciplinary experts assessing the quality of the evidence and the strength of recommendations and offer a clear explanation of logical relationships between various care options and health outcomes.

METHODS

The methods utilized included the development of objectives and key questions for the various facets of opioid prescribing practice. Also utilized were employment of trustworthy standards, and appropriate disclosures of conflicts of interest(s). The literature pertaining to opioid use, abuse, effectiveness, and adverse consequences was reviewed. The recommendations were developed after the appropriate review of text and questions by a panel of multidisciplinary subject matter experts, who tabulated comments, incorporated changes, and developed focal responses to questions posed. The multidisciplinary panel finalized 20 guideline recommendations for prescription of opioids for chronic non-cancer pain. Summary of the results showed over 90% agreement for the final 20 recommendations with strong consensus. The consensus guidelines included 4 sections specific to opioid therapy with 1) ten recommendations particular to initial steps of opioid therapy; 2) five recommendations for assessment of effectiveness of opioid therapy; 3) three recommendations regarding monitoring adherence and side effects; and 4) two general, final phase recommendations.

LIMITATIONS

There is a continued paucity of literature of long-term opioid therapy addressing chronic non-cancer pain. Further, significant biases exist in the preparation of guidelines, which has led to highly variable rules and regulations across various states.

CONCLUSION

These guidelines were developed based upon a comprehensive review of the literature, consensus among expert panelists, and in alignment with patient preferences, and shared decision-making so as to improve the long-term pain relief and function in patients with chronic non-cancer pain. Consequently, it was concluded - and herein recommended - that chronic opioid therapy should be provided in low doses with appropriate adherence monitoring and understanding of adverse events only to those patients with a proven medical necessity, and who exhibit stable improvement in both pain relief and activities of daily function, either independently or in conjunction with other modalities of treatments.

Complex Regional Pain Syndrome: Evidence-Based Advances in Concepts and Treatments

PURPOSE OF REVIEW

This review presents the most current information about the epidemiology of complex regional pain syndrome (CRPS), classification and diagnostic criteria, childhood CRPS, subtypes, pathophysiology, conventional and less conventional treatments, and preventive strategies.

RECENT FINDINGS

CRPS is a painful disorder with multifactorial pathophysiology. The data describe sensitization of the central and peripheral nervous systems, inflammation, possible genetic factors, sympatho-afferent coupling, autoimmunity, and mental health factors as contributors to the syndrome. In addition to conventional subtypes (type I and type II), cluster analyses have uncovered other proposed subtypes. Prevalence of CRPS is approximately 1.2%, female gender is consistently associated with a higher risk of development, and substantial physical, emotional, and financial costs can result from the syndrome. Children with CRPS seem to benefit from multifaceted physical therapy leading to a high percentage of symptom-free patients. The best available evidence along with standard clinical practice supports pharmacological agents, physical and occupational therapy, sympathetic blocks for engaging physical restoration, steroids for acute CRPS, neuromodulation, ketamine, and intrathecal baclofen as therapeutic approaches. There are many emerging treatments that can be considered as a part of individualized, patient-centered care. Vitamin C may be preventive. CRPS can lead to progressively painful sensory and vascular changes, edema, limb weakness, and trophic disturbances, all of which substantially erode healthy living. Despite some progress in research, more comprehensive basic science investigation is needed to clarify the molecular mechanisms of the disease so that targeted treatments can be developed for better outcomes. Incorporating a variety of standard therapies with different modes of action may offer the most effective analgesia. Introducing less conventional approaches may also be helpful when traditional treatments fail to provide sufficient improvement.

Antimicrobial therapies for chronic pain (part 2): the prevention and treatment of chronic pain

The discovery and development of antimicrobial therapies represents one of the most significant advancements in modern medicine. Although the primary therapeutic intent of antimicrobials is to eliminate their target pathogens, several antimicrobials have been shown to provide analgesia as a secondary benefit. Antimicrobials have demonstrated analgesic effects in conditions that involve dysbiosis or potential subclinical infection (e.g ., chronic low back pain with Modic type 1 changes; chronic prostatitis/chronic pelvic pain; irritable bowel syndrome; inflammatory bowel disease; functional gastrointestinal disorders/dyspepsia; myalgic encephalomyelitis/chronic fatigue syndrome), and might even prevent the chronification of pain after acute infections that are associated with excessive systemic inflammation (e.g ., post COVID-19 condition/long Covid, rheumatic fever). Clinical studies often assess the analgesic effects of antimicrobial therapies in an observational manner, without the ability to identify causative relationships, and significant gaps in the understanding remain regarding the analgesic potential of antimicrobials. Numerous interrelated patient-specific, antimicrobial-specific, and disease-specific factors altogether contribute to the perception and experience of pain, and each of these requires further study. Given worldwide concerns regarding antimicrobial resistance, antimicrobials must continue to be used judiciously and are unlikely to be repurposed as primary analgesic medications. However, when equipoise exists among several antimicrobial treatment options, the potential analgesic benefits of certain antimicrobial agents might be a valuable aspect to consider in clinical decision-making. This article (the second in a two-part series) aims to comprehensively review the evidence on the prevention and treatment of chronic pain using antimicrobial therapies and suggest a framework for future studies on this topic.

Antimicrobial therapies for chronic pain (part 1): analgesic mechanisms

There is increasing evidence that the relationship between chronic pain and infections is complex and intertwined. Bacterial and viral infections can cause pain through numerous mechanisms such as direct tissue damage and inflammation, the induction of excessive immunologic activity, and the development of peripheral or central sensitization. Treating infections might relieve pain by attenuating these processes, but a growing body of literature suggests that some antimicrobial therapies confer analgesic effects, including for nociceptive and neuropathic pain symptoms, and affective components of pain. The analgesic mechanisms of antimicrobials are indirect, but might be conceptualized into two broad categories: 1) the reduction of the infectious burden and associated pro-inflammatory processes; and 2) the inhibition of signaling processes (e.g., enzymatic and cytokine activity) necessary for nociception and maladaptive neuroplastic changes via off-target effects (unintended binding sites). For the former, there is evidence that symptoms of chronic low back pain (when associated with Modic type 1 changes), irritable bowel syndrome, inflammatory bowel disease, chronic pelvic pain, and functional dyspepsia might be improved after antibiotic treatment, though significant questions remain regarding specific regimens and dose, and which subpopulations are most likely to benefit. For the latter, there is evidence that several antimicrobial classes and medications exert analgesic effects independent of their reduction of infectious burden, and these include cephalosporins, ribavirin, chloroquine derivatives, rapalogues, minocycline, dapsone, and piscidin-1. This article aims to comprehensively review the existing literature for antimicrobial agents that have demonstrated analgesic efficacy in preclinical or clinical studies.

Perioperative and anesthetic considerations for the management of neuromodulation systems

The use of neuromodulation systems is increasing for the treatment of various pathologies ranging from movement disorders to urinary incontinence to chronic pain syndromes. While the type of neuromodulation devices varies, they are largely categorized as intracranial (eg, deep brain stimulation), neuraxial (eg, spinal cord stimulation, dorsal root ganglion stimulation, and intrathecal drug delivery systems), or peripheral (eg, sacral nerve stimulation and peripheral nerve stimulation) systems. Given the increasing prevalence of these systems in the overall population, it is important for anesthesiologists, surgeons, and the perioperative healthcare team to familiarize themselves with these systems and their unique perioperative considerations. In this review, we explore and highlight the various neuromodulation systems, their general perioperative considerations, and notable special circumstances for perioperative management.

Emerging Evidence for Intrathecal Management of Neuropathic Pain Following Spinal Cord Injury

A high prevalence of patients with spinal cord injury (SCI) suffer from chronic neuropathic pain. Unfortunately, the precise pathophysiological mechanisms underlying this phenomenon have yet to be clearly elucidated and targeted treatments are largely lacking. As an unfortunate consequence, neuropathic pain in the population with SCI is refractory to standard of care treatments and represents a significant contributor to morbidity and suffering. In recent years, advances from SCI-specific animal studies and translational models have furthered our understanding of the neuronal excitability, glial dysregulation, and chronic inflammation processes that facilitate neuropathic pain. These developments have served advantageously to facilitate exploration into the use of neuromodulation as a treatment modality. The use of intrathecal drug delivery (IDD), with novel pharmacotherapies, to treat chronic neuropathic pain has gained particular attention in both pre-clinical and clinical contexts. In this evidence-based narrative review, we provide a comprehensive exploration into the emerging evidence for the pathogenesis of neuropathic pain following SCI, the evidence basis for IDD as a therapeutic strategy, and novel pharmacologics across impactful animal and clinical studies.

An overview of painful diabetic peripheral neuropathy: Diagnosis and treatment advancements

Diabetes mellitus remains a public health problem, affecting 422 million people worldwide. Currently, there is no consensus around treating painful diabetic peripheral neuropathy in a step-wise manner. Among the non-pharmacological interventions, neuromodulation has become a promising alternative. Over the past decade, significant clinical trials have paved the way for prompt inclusion of high-frequency spinal cord stimulation within the painful diabetic peripheral neuropathy treatment algorithm. This article aims to provide an updated evidence-based approach for the management of painful diabetic peripheral neuropathy.

Combination Intrathecal Drug Therapy Strategies for Pain Management

BACKGROUND

Numerous combination intrathecal drug therapy (CIDT) strategies exist and are utilized for varying pain syndromes, typically when monotherapy dose escalation or medication alternation is deemed untenable or unfeasible. Unfortunately, the supportive evidence basis for the use of these strategies and specific drug combinations is generally lacking and unclear, with many medications being used for off-label indications.

OBJECTIVE

In this manuscript, we provide a robust exploration and analysis of the literature to provide an evidence-based narrative for the use of CIDT strategies in regard to clinical indications, pharmacologic parameters, specific drug combinations, safety profiles, and future directions.

STUDY DESIGN

Narrative review.

METHODS

This was an evidence based narrative performed after extensive review of the literature.

RESULTS

Variances in intrathecal pharmacokinetics and pharmacodynamics are utilized advantageously with CIDT strategies to achieve improved analgesic benefit; however, appropriate use may be limited by increased or compounded risk of adverse effects. The supportive evidence for CIDT use for chronic pain conditions is largely lacking and limited to small, uncontrolled, observational studies, with many having various confounding factors, including a lack of standardized dosing. The most evidenced CIDT strategies include polyanalgesia with morphine-ziconotide, opioid-clonidine, and morphine-bupivacaine. Notably, in addition to pain relief, morphine-bupivacaine has been shown to decrease early opioid escalation requirements.

LIMITATIONS

The supportive evidence for CIDT use for chronic pain conditions is largely lacking and limited to small, uncontrolled, observational studies, with many having various confounding factors including a lack of standardized dosing.

CONCLUSIONS

CIDT strategies and polyanalgesia combinations can be effective for treating various patient populations with chronic pain. The appropriate use of these strategies may be limited by increased or compounded risk of adverse effects, both of which are highly patient and scenario dependent. Therefore, practitioners should maintain a particularly low threshold of suspicion for adverse effects in patients with CIDT such that safety profiles associated with this therapy can be favorably maintained.

Use of Radiofrequency Ablation for the Management of Headache: A Systematic Review

BACKGROUND

Headache is a very common condition that affects 5-9% of men and 12-25% of women in North America and Europe. Globally, the prevalence of active headaches among adults is 47%. The most common type of headache is tension headaches (38% of adults), followed by migraines (10%), and chronic headaches (3%). While the majority of headaches are benign, the disorder can severely negatively influence a patients' quality of life, which is directly reflected in societal costs.

OBJECTIVE

The objective of this review was to summarize available evidence behind radiofrequency ablation (RFA) for headache, including pain outcome measures, secondary outcomes, and complications.

STUDY DESIGN

Systematic review.

SETTING

This systematic review examined studies that applied the use of RFA for management of headache.

METHODS

This systematic review was reported following the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). Two reviewers independently scored the methodological quality of the selected studies. Due to heterogeneity of studies, a best-evidence synthesis of the available prognostic factors was provided.

RESULTS

In the present investigation, we evaluated 18 studies composed of 6 randomized controlled trials (RCTs), 6 prospective studies, and 6 retrospective studies. All the studies assessed pain improvement with RFA in patients with headache. Most studies targeted the occipital nerve for treatment. Complications were mostly mild and self-limiting, including eyelid swelling, rash, superficial infection of the procedural site, and worsening of headache.

LIMITATIONS

A large variability in definitions of trigeminal neuralgia, radiofrequency technique, and patient selection bias was observed in our selected cohort of studies. In addition, there is a paucity of strong longitudinal RCTs and prospective studies.

CONCLUSION

Our review discusses several studies that suggest the efficacy of RFA in the treatment of headaches. Outcomes varied based on the difference in approaches regarding continuous radiofrequency versus pulsed radiofrequency, temperature, and duration of administration. The majority of the studies discussed in this review indicate a therapeutic benefit of RFA for headaches over a short-term period. Pain outcomes beyond one year are understudied and further studies are needed to determine the long-term effects of RFA for headaches.

Radiofrequency Ablation for Thoracic and Abdominal Chronic Pain Syndromes

Chronic thoracic pain and chronic abdominal pain are common conditions that can significantly affect quality of life. Pain syndromes encompassing a variety of causes, including cancer pain, neuritis, and postsurgical pain, are traditionally managed by the use of pharmacologic therapy; however, many cases are refractory to these conservative methods. Radiofrequency ablation (RFA) has been increasingly used as a tool to treat resistant, chronic pain of both thoracic and abdominal origin. Multiple cases and trials have been reported that show the efficacy of RFA in the treatment of these chronic pain conditions.

Chronic Pain in Patients with Rheumatoid Arthritis

PURPOSE OF REVIEW

Chronic pain is highly prevalent in patients with rheumatoid arthritis (RA) and can cause various physical and psychological impairments. Unfortunately, the appropriate diagnosis of chronic pain syndromes in this population can be challenging because pain may be primary to RA-specific inflammation and/or secondary to other conditions, typically osteoarthritis (OA) and fibromyalgia (FM). This disparity further poses a clinical challenge, given that chronic pain can often be discordant or undetected with standard RA-specific surveillance strategies, including serological markers and imaging studies. In this review, we provide a robust exploration of chronic pain in the RA population with emphasis on epidemiology, mechanisms, and management strategies.

RECENT FINDINGS

Chronic pain associated with RA typically occurs in patients with anxiety, female sex, and elevated inflammatory status. Up to 50% of these patients are thought to have chronic pain despite appropriate inflammatory suppression, typically due to peripheral and central sensitization as well as secondary OA and FM. In addition to the standard-of-care management for OA and FM, patients with RA and chronic pain benefit from behavioral and psychological treatment options. Moreover, early and multimodal therapies, including non-pharmacological, pharmacological, interventional, and surgical strategies, exist, albeit with varying efficacy, to help suppress inflammation, provide necessary analgesia, and optimize functional outcomes. Overall, chronic pain in RA is a difficult entity for both patients and providers. Early diagnosis, improved understanding of its mechanisms, and initiation of early, targeted approaches to pain control may help to improve outcomes in this population.

Many Faces of the Hidden Souls: Medical and Neurological Complications and Comorbidities in Disorders of Consciousness

Early and goal-directed management of complications and comorbidities is imperative to facilitate neurorecovery and to optimize outcomes of disorders of consciousness (DoC). This is the first large retrospective cohort study on the primary medical and neurological complications and comorbidities in persons with DoC. A total of 146 patients admitted to a specialized inpatient DoC rehabilitation program from 1 January 2014 to 31 October 2018 were included. The incidences of those conditions since their initial brain injuries were reviewed per documentation. They were categorized into reversible causes of DoC, confounders and mimics, and other medical/neurological conditions. The common complications and comorbidities included pneumonia (73.3%), pain (75.3%), pressure ulcers (70.5%), oral and limb apraxia (67.1%), urinary tract infection (69.2%), and 4-limb spasticity (52.7%). Reversible causes of DoC occurred very commonly. Conditions that may confound the diagnosis of DoC occurred at surprisingly high rates. Conditions that may be a source of pain occurred not infrequently. Among those that may diminish or confound the level of consciousness, 4.8 ± 2.0 conditions were identified per patient. In conclusion, high rates of various complications and comorbidities occurred in persons with DoC. Correcting reversible causes, identifying confounders and mimics, and managing general consequences need to be seriously considered in clinical practice.

Neuromodulation for Pain Management in the Inpatient Setting: A Narrative Review

Pain is highly prevalent and pharmacological therapy is not always efficacious. There are a few pathophysiological reasons to believe that neuromodulation would increase the rate of success of pain management. This review article is focused on that aspect, discussing non-invasive or minimally invasive neuromodulation techniques in both the inpatient and outpatient setting. This article provides an in-depth discussion of the multiple neuromodulation techniques available over time to be suitable and effective when used as analgesic therapies for chronic pain. We reviewed the literature and discussed all available neuromodulation options that were tested in the inpatient and outpatient setting. Neuromodulation plays a very important role in treating chronic pain in both inpatient and outpatient setting.

Radiotherapy-Specific Chronic Pain Syndromes in the Cancer Population: An Evidence-Based Narrative Review

While radiation therapy is increasingly utilized in the treatment paradigm of many solid cancers, the chronic effects of radiation therapies are poorly characterized. Notably, understanding radiation-specific chronic pain syndromes is paramount given that the diagnosis and management of these conditions can serve to prevent long-standing functional impairments, optimize quality of life, and even allow for continued radiotherapy candidacy. These radiation-specific chronic pain phenomena include dermatitis, mucositis, enteritis, connective tissue fibrosis, lymphedema, and neuropathic pain syndromes. It is necessary to maintain a low threshold of suspicion for appropriately diagnosing these conditions as there exists a variance in when these symptoms arise after radiation. However, we present key epidemiological data delineating vulnerable cancer populations for each pain syndrome along with the available evidence for the management for each specific condition.

Utility of Electrical Neuromodulation for Treating Chronic Pain Syndromes in the Pediatric Setting: A Systematic Review

OBJECTIVES

Chronic pain syndromes in children can carry significant threats to psychological well-being, opioid overuse, functional impairments, and severe disability. While several high-level studies, almost exclusively in adults, have demonstrated the utility of implantable electrical neuromodulation systems for treating various chronic pain syndromes, there exists a paucity of pediatric-specific evidence. Unfortunately, evidence and practice patterns established from adults may not be fully translatable to children given differences in disease manifestations and anatomical variances.

MATERIALS AND METHODS

We performed a systematic review using conventional PRISMA methodology to identify studies reporting use of implantable electrical neuromodulation systems in children. The primary outcome parameters collected were analgesic relief and functional benefits. Additionally, previous interventions attempted, neuromodulation parameters, and limitations were collected as reported.

RESULTS

A total of 11 studies was identified, which described 19 patients who were refractory to multidisciplinary pain management strategies. The cohort was mostly adolescent (18/19), suffered from CRPS (14/19), and received SCS (17/19). Nearly all patients, both those with CRPS (13/14) and non-CRPS conditions (4/4), reported significant pain relief and functional recovery following neuromodulation. There were no severe complications reported; limitations included suboptimal benefit or loss of analgesia (3/19), lead or device revision (3/19), and subcutaneous infection (1/19), all of which were congruent with adult outcomes.

CONCLUSION

There exist children with chronic pain refractory to standard of care approaches who could be considered for neuromodulation interventions. The existing data, which was limited and from a low tier of evidence, suggest that these interventions are relatively safe and provide meaningful pain reduction and functional improvements. While not previously reported, we recommend careful consideration of the pubertal growth spurt prior to device lead placement-if reasonable and appropriate-given the possibility of inferior lead migration with physiologic growth in patients with SCS devices or foraminal extrusion in patients with dorsal root ganglion stimulation devices.

Dorsal Root Ganglion Stimulation for the Treatment of Non-Complex Regional Pain Syndrome Related Chronic Pain Syndromes: A Systematic Review

BACKGROUND

While the majority of indications and approvals for dorsal root ganglion stimulation (DRGS) are for the refractory management of complex regional pain syndrome (CRPS), emerging evidence has suggested that DRGS may be favorably used for a plethora of other chronic pain phenomena. Consequently, we aimed to characterize the use and efficacy of DRGS for these non-CRPS-related chronic pain syndromes.

MATERIALS AND METHODS

A systematic review of clinical studies demonstrating the use of DRGS for non-CRPS-related chronic pain syndromes. The literature search was performed using PubMed, Cochrane Library, and CINAHL plus across August and September 2020.

RESULTS

A total of 28 reports comprising 354 total patients were included in the analysis. Of the chronic pain syndromes presented, axial low back pain, chronic pelvic and groin pain, other peripheral neuropathies, and studies with multiple concomitant pain syndromes, a majority demonstrated >50% mean pain reduction at the time of last follow-up following DRGS. Physical function, quality of life (QOL), and lesser pain medication usage also were repeatedly reported to be significantly improved.

CONCLUSIONS

DRGS continues to lack supportive evidence from well designed, high level studies and recommendations from consensus committee experts. However, we present repeated and consistent evidence from lower level studies showing success with the use of DRGS for various non-CRPS chronic pain syndromes in reducing pain along with increasing function and QOL from one week to three years. Due to such low-level, high bias evidence, we strongly encourage the continuation of high-level studies in order to provide a stronger foundation for the use of DRGS in non-CRPS chronic pain patients. However, it may be reasonable and appropriate to evaluate patients for DRGS candidacy on a case-by-case basis particularly if they manifest focal pain syndromes refractory to noninterventional measures and may not be ideal candidates for other forms of neuromodulation.

Use of Cryotherapy for Managing Chronic Pain: An Evidence-Based Narrative

Background

Cryotherapy has been used to reduce chronic pain for many years due in part to its ease of use, affordability, and simplicity. It can be applied either locally (e.g., ice packs) or non-locally (e.g., partial and whole-body cryotherapy) depending on the location of the pain.

Objectives

To determine the overall effectiveness of cryotherapy at reducing chronic pain by characterizing the currently available evidence supporting the use and effects of cryotherapy on chronic pain associated with chronic diseases.

Study Design

A narrative review of original research studies assessing the efficacy of cryotherapy in alleviating chronic pain.

Methods

A PubMed database search was performed to find human studies between the years 2000 and 2020 that included the application of cryotherapy in patients with chronic pain associated with chronic diseases. A review of the relevant references was also performed to gather more articles. Data was extracted, summarized into tables, and qualitatively analyzed.

Results

Twenty-five studies (22 randomized controlled trials, one prospective analysis, 1 one-group pretest/posttest study, and one case–control study) were included after the literature search. Both local and non-local cryotherapy applications show promise in reducing chronic pain associated with various chronic diseases including those of rheumatic and degenerative origin. Cryotherapy appears to be a safe therapy in carefully selected patients, with only minimal adverse effects reported in the literature.

Limitations

Meta-analysis was not possible given the many differences between studies. Cross-study data homogenization and comparison between studies proved fairly difficult due to the lack of standardized studies, various uses and practice types of cryotherapy, and lack of control groups in some studies.

Conclusions

Local and non-local cryotherapy can be low-risk and easy treatment options to add in the management of chronic pain in carefully selected patients. However, long-term effects, a standardized approach, and careful study of other chronic pain syndromes should be considered in future research to further support the use of cryotherapy in the management of chronic pain.

Spinal Cord Stimulation for Chronic Pain Syndromes: A Review of Considerations in Practice Management

BACKGROUND

Chronic pain syndromes are clinically challenging to treat, and management with opioid medications is increasingly shown to be inappropriate and ineffective. Spinal cord stimulation (SCS) has been demonstrated across numerous high-quality and well-designed studies to be effective in treating various refractory chronic pain. The efficacy and overall success of SCS is highly dependent on compliance to and consideration of various practice patterns.

OBJECTIVE

This manuscript is intended to compile and present comprehensive recommendations for key SCS management principles including: a) patient selection criteria, b) efficacy of SCS for various conditions, c) discussion of SCS waveforms, d) trial and permanent implantation considerations, e) periprocedural management, and f) complications and adverse events.

STUDY DESIGN

An evidence-based narrative review.

METHODS

PubMed, Medline, Cochrane Library, prior systematic reviews, and reference lists were screened by 2 separate authors for all randomized trials, meta-analyses, and observational studies relevant to each of the aforementioned management principles and considered for study inclusion.

RESULTS

All high-level evidence studies that explored the various facets of SCS practice management were included for review.

LIMITATIONS

Both continued investigation into, and practice implementation of, the various facets of SCS management are necessary to optimize patient outcomes.

CONCLUSION

Implementation of and adherence to the evidenced-based recommendations delineated in this publication may help optimize efficacy outcomes and maintain safety profiles for persons treated with SCS interventions.

Intrathecal Drug Delivery for Chronic Pain Syndromes: A Review of Considerations in Practice Management

BACKGROUND

Chronic pain syndromes are poorly understood and challenging to treat. However, intrathecal drug delivery systems (IDDS) have been shown to have good efficacy in treating various pain subtypes and patient populations. The success of IDDS interventions is largely dependent on consideration of and adherence to varying practice patterns.

OBJECTIVES

We aimed to review and report on the evidence basis for various considerations in IDDS practice management including: (1) patient selection and periprocedural criteria, (2) efficacy of IDDS for various conditions, (3) intrathecal medications, (4) drug delivery systems, (5) trial and implantation, (6) complications and adverse events, and (7) chronic follow-up.

STUDY DESIGN

We conducted an evidence-based narrative review.

METHODS

PubMed, Medline, Cochrane Library, prior systematic reviews, and reference lists were screened by 2 separate authors for all randomized trials, meta-analyses, and observational studies relevant to each of the aforementioned management principles and were considered for study inclusion.

RESULTS

All high-level evidence studies that explored the various facets for IDDS practice management were included for review.

LIMITATIONS

Despite existing evidence basis for practice considerations, current practice patterns are highly practitioner dependent. More and continued high-level evidence is necessary to support, affirm, and dictate principles in practice considerations.

CONCLUSIONS

Incorporation of the principles found in this evidence-based narrative, which is comprised of the highest level of evidence supportive of various facets of IDDS practice management, is essential to optimize outcomes, treatment efficacy, and safety profiles.

Obesity Trends Amongst Hospitalized Patients with Spinal Cord Stimulator Implants

INTRODUCTION

Chronic pain remains an important public health problem as it continues to increase healthcare-related cost. Comorbidities like obesity have been associated with efficacy of spinal cord stimulator (SCS) therapy and worse outcomes. The goal of this study is to investigate the trends of obesity amongst hospitalized patients with SCS therapy as well as healthcare utilization outcomes.

METHODS

Using the International Classification of Diseases (ICD) ninth and tenth procedure and diagnosis code, we investigated the National Inpatient Sample (NIS) for patients with SCS implants between 2011 and 2015. Patients received a diagnosis of obesity based on the following categories: class I, II and III obesity. Age, gender, and comorbid conditions of patients with obesity were matched 1:1 on propensity score to those without obesity diagnosis. Our primary outcome was defined as trend of obesity diagnosis. Our secondary outcome, healthcare utilization, included in-hospital cost, length of stay, and discharge location.

RESULTS

Between 2011 and 2015, a total of 3893 patients with SCS implants were identified (average age 56 ± 15 years, 58% female, 0.70 ± 1.1 Charlson Comorbidity Index, CCI). Of this cohort, 640 patients were identified as obese. The proportion of patients with obesity diagnosis increased significantly from 13.75% in 2011 to 19.36% in 2015 (p < 0.001). After 1:1 matching on propensity score, 597 patients with obesity were successfully matched to 597 patients without obesity. The total hospital cost for SCS patients with obesity (median $104,845, IQR $74,648-144,292) was not significantly different from patients without obesity diagnosis (median $111,092, IQR $68,990-145,459) (p = 0.161).

CONCLUSIONS

The data from our study suggests that there is an increasing rate of obesity diagnosis amongst patients with SCS therapy. However, there was no difference in healthcare utilization between patients with and without obesity. Additional studies may provide more insight into our findings.

Comparison of Spinal Cord Stimulation Waveforms for Treating Chronic Low Back Pain: Systematic Review and Meta-Analysis

BACKGROUND

The treatment of chronic refractory low back pain (LBP) is challenging. Conservative and pharmacologic options have demonstrated limited efficacy. Spinal cord stimulation (SCS) has been shown to be effective in reducing chronic LBP in various contexts. With emerging SCS technologies, the collective evidence of novel waveforms relative to traditional tonic stimulation for treating chronic LBP has yet to be clearly characterized.

OBJECTIVES

To provide evidence for various SCS waveforms-tonic, burst, and high frequency (HF)-relative to each other for treating chronic LBP.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

PubMed, Medline, Cochrane Library, prior systematic reviews, and reference lists were screened by 2 separate authors for all randomized trials and prospective cohort studies comparing different SCS waveforms for treatment of chronic LBP.

RESULTS

We identified 11 studies that included waveform comparisons for treating chronic LBP. Of these, 6 studies compared burst versus tonic, 2 studies compared burst versus HF, and 3 studies compared tonic versus HF. A meta-analysis of 5 studies comparing burst versus tonic was conducted and revealed pooled superiority of burst over tonic in pain reduction. One study comparing burst versus tonic was excluded given technical challenges in data extraction.

LIMITATIONS

Both randomized controlled trials and prospective cohort studies were included for meta-analysis. Several studies included a high risk of bias in at least one domain.

CONCLUSIONS

Burst stimulation is superior to tonic stimulation for treating chronic LBP. However, superiority among other waveforms has yet to be clearly established given some heterogeneity and limitations in evidence. Given the relative novelty of burst and HF SCS waveforms, evidence of longitudinal efficacy is needed.

Pain Syndromes Secondary to Cluneal Nerve Entrapment

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of the cluneal nerves, present a summary of pain syndromes secondary to clunealgia, and evaluate current literature for diagnostic and treatment modalities.

RECENT FINDINGS

Multiple trials and studies have reported success with numerous modalities ranging from nerve blocks, neuroablation, and even peripheral neuromodulation with varying degrees of clinical benefit. Cluneal nerve entrapment or chronic impingement can cause buttock pain or referred pain to nearby areas including the lower back, pelvic area, or even the lower extremities. Clunealgias and associated pain syndromes can often be challenging to diagnose and differentiate. An appreciation of the pathophysiology of clunealgias can assist with patient selection for interventional pain strategies targeted towards the cluneal nerves, including nerve blocks, neuroablation, and peripheral neuromodulation. More research is needed to better delineate the efficacy of these procedures for clunealgias.

Correlating computed tomography pulmonary angiography signs of right ventricular strain in pulmonary embolisms to clinical outcomes

INTRODUCTION:

Right ventricular strain (RVS) in pulmonary embolism (PE) can be used to stratify risk and direct intervention. The clinical significance of computed tomography pulmonary angiogram (CTPA)-derived radiologic signs of RVS, however, remains incompletely characterized. We retrospectively analyzed a cohort of persons with acute PE to determine which, if any, findings of RVS on CTPA correlate with clinical outcomes.

METHODS:

All patients with PE diagnosed on CTPA from March 2013 through February 2015 at Lyndon B. Johnson Hospital were identified. Their records were retrospectively reviewed to identify length of stay, intensive care unit (ICU) placement, hemodynamic failure, use of thrombolytics, vasopressor requirement, mechanical ventilation, and attributable mortality. Three radiologists, blinded to clinical outcomes, separately reviewed the cohort's CTPAs to identify signs of RVS – pulmonary trunk size, internal size of the right and left ventricles, paradoxical interventricular septal bowing, inferior vena cava (IVC) contrast reflux, and hepatic vein contrast reflux.

RESULTS:

In our cohort of 102 persons, 12 demonstrated hemodynamic failure, 13 required ICU placement, 3 received thrombolysis, and 5 had death attributable to PE. The greatest interobserver agreement among radiologists existed for the presence of increased pulmonary trunk size (0.76 kappa by %agreement) and hepatic vein contrast reflux (0.92 kappa by %agreement). A multiple regression analysis found that when 100% radiologist agreement existed, presence of paradoxical intravenous septal bowing predicted thrombolytic usage (P = 0.02), and the presence of IVC reflux predicted attributable mortality (P = 0.03).

CONCLUSION:

Only IVC contrast reflux was associated with increased mortality, and no other sign of RVS on CTPA correlated with clinical outcomes. This suggests that most signs of RVS on CTPA do not reliably predict PE severity. Therefore, RVS seen by CTPA should be used cautiously in weighing the decision to initiate thrombolytics.

Exploration of Gender-Specific Authorship Disparities in the Pain Medicine Literature

BACKGROUND

Given the readily increasing membership of the pain physician community, efforts toward correcting notable gender disparities are instrumental. The under-representation of women is particularly prevalent within leadership roles in academic medicine, thought to be driven largely by diminished research efforts. Consequently, we aimed to characterize gender differences among the highest impact pain literature.

METHODS

The 20 highest cited articles per year from 2014 to 2018 were extracted from each of seven impactful journals affiliated to the largest pain medicine societies. Collected data from each article included genders of the first and last authors, the number of citations accumulated and the journal impact factor at the time of publication.

RESULTS

Across all considered literature, female authors were surprisingly not under-represented when considering the national prevalence of female pain physicians. However, more in-depth analysis found trends toward significance to suggest that female authorship was relatively diminished within more impactful and higher cited literature. When exploring gender-gender collaboration patterns, we found that male authors were favored over female counterparts with statistical significance; it must be noted that this likelihood analysis and preference toward male authors may be statistically obfuscated by the high prevalence of male authors. Nonetheless, these findings help to quantify overt, demonstrated disparity patterns. Of note, this inequity may also be fully secondary to the lower number of female pain physicians and/or those involved in research endeavors and decreased number of submissions from female physicians. Establishing gender discrimination patterns as causal factors in such disparities can be extremely challenging to determine.

CONCLUSION

In our analysis of authorship between genders within the context of pain medicine literature, we found trends, although non-significant, toward women being lesser represented in the more impactful literature. We suggest that these inequities are possibly resultant of a markedly small and outnumbered female pain physician membership that has yet to achieve a critical mass and possible implicit gender biases that may restrict female authorship. However, further exploration and analysis of this issue are necessary to more clearly illuminate which systemic deficits exist and how they may, in turn, be corrected with cultural and macroscopic organizational-driven change.

Phenol Neurolysis for Management of Focal Spasticity in the Distal Upper Extremity

BACKGROUND

When managing patients with focal spasticity, phenol neurolysis is often avoided largely because of its presumed poor adverse effect profile. It is suggested that dysesthesias may be more common with phenol neurolysis of the mixed sensorimotor nerves (eg, radial, median, and ulnar nerves) compared to neurolysis of pure motor nerves. However, these risks may be mitigated with precise localization of pure motor branches by ultrasound and electrical stimulation (EStim).

OBJECTIVE

To explore practice patterns of phenol neurolysis to distal upper extremity mixed sensorimotor nerves with ultrasound and EStim guidance.

DESIGN

A retrospective analysis of all neurolysis procedure records at a single institution from January 2013 to February 2018. Demographic and clinical variables including primary neurological diagnosis, concurrent spasticity treatments, nerves injected, phenol dosage and adverse events were abstracted from the electronic medical records.

PARTICIPANTS

57 patients who received phenol neurolysis with ultrasound and EStim guidance for spasticity management to radial, median, or ulnar nerves.

MAIN OUTCOME MEASURES

Reported adverse effects.

RESULTS

A total of 57 patients who collectively received neurolysis to 139 nerves across 102 encounters, met inclusion criteria. Most prevalent diagnoses included traumatic brain injury (N = 27, 47.4%) and stroke (N = 18, 31.6%), with a smaller subset having spinal cord injury (N = 10, 17.5%). Most patients received concomitant chemodenervation with botulinum toxin (N = 44, 77.2%). The average phenol dosage per nerve was 1.8 mL, with a range of 0.5-9.0 mL. Reported adverse effects included three cases of prolonged pain, but no dysesthesias were reported during the follow-up period (>40 days).

CONCLUSIONS

Phenol neurolysis with ultrasound and EStim guidance was successfully and safely used to manage focal spasticity in the distal upper extremity.

LEVEL OF EVIDENCE

III.

Observations of Autonomic Variability Following Central Neuromodulation for Chronic Neuropathic Pain in Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) persons with chronic neuropathic pain (NP) demonstrate maladaptive autonomic profiles compared to SCI counterparts without NP (SCI - NP) or able-bodied (AB) controls. These aberrations may be secondary to maladaptive neuroplasticity in the shared circuitry of the pain neuromatrix-central autonomic network interface (PNM-CAN). In this study, we explored the proposed PNM-CAN mechanism in SCI + NP and AB cohorts following centrally-directed neuromodulation to assess if the PNM and CAN are capable of being differentially modulated.

MATERIALS AND METHODS

Central neuromodulation was administered via breathing-controlled electrical stimulation (BreEStim), previously evidenced to operate at the PNM. To quantify CAN activity, conventional heart rate variability (HRV) recordings were used to gather time and frequency domain parameters of autonomic modulation. SCI + NP (n = 10) and AB (n = 13) cohorts received null and active BreEStim randomly in crossover fashion. HRV data were gathered pretest and 30 minutes posttest. Pain modulation was quantified at both time-points by visual analog scale (VAS) for SCI + NP persons and electrical detection and pain threshold levels (EDT, EPT) for AB persons.

RESULTS

Following active BreEStim only, SCI + NP persons demonstrated increased parasympathetic tone (increased NN50, p = 0.03, and pNN50, p = 0.02, HRV parameters). This parasympathetic restoration was associated with analgesia (VAS reduction, p < 0.01). Similarly, AB persons demonstrated increased noxious tolerance (increased EPT, p = 0.03, with preserved EDL, p = 0.78) only following active BreEStim. However, this increased pain threshold was not associated with autonomic changes.

CONCLUSIONS

Central modulation targeting the PNM produced autonomic changes in SCI + NP persons but not AB persons. These findings suggest that AB persons exhibit intact CAN mechanisms capable of compensating for PNM aberrations or simply that SCI + NP persons exhibit altered PNM-CAN machinery altogether. Our collective findings confirm the interconnectedness and maladaptive plasticity of PNM-CAN machinery in SCI + NP persons and suggest that the PNM and CAN circuitry can be differentially modulated.

Neuropathic pain modulation after spinal cord injury by breathing-controlled electrical stimulation (BreEStim) is associated with restoration of autonomic dysfunction

BACKGROUND

Recent findings have implicated supraspinal origins from the pain neuromatrix- central autonomic network (PNM-CAN) in the generation of neuropathic pain (NP) after spinal cord injury (SCI). The aim of this study was to further investigate the theorized PNM-CAN mechanisms in persons with SCI by using a centrally directed pain intervention, provided by breathing-controlled electrical stimulation (BreEStim), to measure resultant autonomic changes measured by time and frequency domain heart rate variability (HRV) analysis.

METHODS

Null and active BreEStim interventions were administered to SCI+NP subjects (n=10) in a random order. HRV data and VAS pain scores were collected at resting pre-test and 30 minutes post-test time points. Resting HRV data were also collected from SCI-NP subjects (n=11).

RESULTS

SCI+NP subjects demonstrated a lower baseline HRV and parasympathetic tone, via SD of the normal-to-normal intervals (SDNN) and low frequency (LF) parameters, compared with SCI-NP subjects. However, following active BreEStim, SCI+NP subjects exhibited an increase in HRV and parasympathetic tone, most notably via pairs of successive R-R beat lengths varying by greater than 50 ms (NN50) and proportion of NN50 for total number of beats (pNN50) parameters along with lower VAS scores. Additionally, the post-test SCI+NP group was found to have a statistically comparable autonomic profile to the SCI-NP group across all HRV variables, including SDNN and LF parameters.

CONCLUSION

The analgesic effects of active BreEStim in SCI+NP subjects were associated with restoration of autonomic dysfunction in this population.

Heart Rate Variability: A Novel Modality for Diagnosing Neuropathic Pain after Spinal Cord Injury

Background: Heart rate variability (HRV), the physiological variance in the heart's R-R interval length, can be analyzed to produce various parameters reflective of one's autonomic balance. HRV analysis may be used to capture those autonomic aberrations associated with chronic neuropathic pain (NP) in spinal cord injury (SCI). This study assesses the capacity of HRV parameters to diagnose NP in an SCI cohort.

Methods: An electrocardiogram (ECG) was collected at rest from able bodied participants (AB, n = 15), participants with SCI only (SCI-NP, n = 11), and those with SCI and NP (SCI+NP, n = 20). HRV parameters were analyzed using conventional time and frequency analysis.

Results: At rest, there were no heart rate differences amongst groups. However, SCI+NP participants demonstrated lower overall HRV, as determined by the SDNN time domain parameter, compared to either AB (p < 0.01) or SCI-NP (p < 0.05) groups. Moreover, AB and SCI-NP participants were statistically comparable for all HRV time and frequency domain parameters. Additional analyses demonstrated no differences in HRV parameters between T4, above vs. T5, below SCI groups (for all parameters: p > 0.15) or between C8, above vs. T1, below SCI groups (p > 0.30).

Conclusions: Participants with SCI and NP exhibit a lower overall HRV, which can be determined by HRV time domain parameter SDNN. HRV analysis is an innovative modality with the capacity for objective quantification of chronic NP in participants with SCI.