IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Transforaminal Injections of Platelet-Rich Plasma Compared with Steroid in Lumbar radiculopathy: A Prospective, Double-Blind Randomized Study

Purpose

To evaluate and compare the clinical efficacy of transforaminal steroid and platelet-rich plasma (PRP) injections in patients with discogenic lumbar radiculopathy.

Methods

60 patients were randomized to be treated with single transforaminal injection of PRP (n = 29) or steroid (methylprednisolone acetate [n = 31]). Clinical assessment was done with Visual analogue scale (VAS), modified Oswestry low back pain disability index (MODI), and straight leg raise test (SLRT). Baseline assessment of outcomes was done followed by post-intervention evaluation at 1, 3, and 6 months. Both groups had similar baseline characteristics.

Results

There was a significant statistical improvement of VAS and MODI in both groups at follow-up (P < 0.05). In PRP group, minimal clinically important change (> 2 cm difference of mean for VAS and > 10-point change in MODI) for both outcome scores was achieved at all follow-up intervals (1, 3, 6 months), while as in steroid group, it was seen only at 1 and 3 months for both VAS and MODI. On intergroup comparison, better results were seen in steroid group at 1 month (P < 0.001 for both VAS and MODI), and in PRP group at 6 months (P < 0.001 for both VAS and MODI) with non-significant difference at 3 months (P = 0.605 for MODI and P = 0.612 for VAS). More than 90% tested SLRT negative in PRP group and 62% in steroid group at 6 months. No serious complications were seen.

Conclusion

Transforaminal injections of PRP and steroid improve short-term (up to 3 months) clinical outcome scores in discogenic lumbar radiculopathy, but clinically meaningful improvements sustaining for 6 months were provided by PRP only.

Interventions for treating pain and disability in adults with complex regional pain syndrome- an overview of systematic reviews

BACKGROUND

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually occurs in a limb following trauma or surgery. It is characterised by persisting pain that is disproportionate in magnitude or duration to the typical course of pain after similar injury. There is currently no consensus regarding the optimal management of CRPS, although a broad range of interventions have been described and are commonly used. This is the first update of the original Cochrane review published in Issue 4, 2013.

OBJECTIVES

To summarise the evidence from Cochrane and non-Cochrane systematic reviews of the efficacy, effectiveness, and safety of any intervention used to reduce pain, disability, or both, in adults with CRPS.

METHODS

We identified Cochrane reviews and non-Cochrane reviews through a systematic search of Ovid MEDLINE, Ovid Embase, Cochrane Database of Systematic Reviews, CINAHL, PEDro, LILACS and Epistemonikos from inception to October 2022, with no language restrictions. We included systematic reviews of randomised controlled trials that included adults (≥18 years) diagnosed with CRPS, using any diagnostic criteria.  Two overview authors independently assessed eligibility, extracted data, and assessed the quality of the reviews and certainty of the evidence using the AMSTAR 2 and GRADE tools respectively. We extracted data for the primary outcomes pain, disability and adverse events, and the secondary outcomes quality of life, emotional well-being, and participants' ratings of satisfaction or improvement with treatment.  MAIN RESULTS: We included six Cochrane and 13 non-Cochrane systematic reviews in the previous version of this overview and five Cochrane and 12 non-Cochrane reviews in the current version. Using the AMSTAR 2 tool, we judged Cochrane reviews to have higher methodological quality than non-Cochrane reviews. The studies in the included reviews were typically small and mostly at high risk of bias or of low methodological quality. We found no high-certainty evidence for any comparison.  There was low-certainty evidence that bisphosphonates may reduce pain intensity post-intervention (standardised mean difference (SMD) -2.6, 95% confidence interval (CI) -1.8 to -3.4, P = 0.001; I2 = 81%; 4 trials, n = 181) and moderate-certainty evidence that they are probably associated with increased adverse events of any nature (risk ratio (RR) 2.10, 95% CI 1.27 to 3.47; number needed to treat for an additional harmful outcome (NNTH) 4.6, 95% CI 2.4 to 168.0; 4 trials, n = 181).  There was moderate-certainty evidence that lidocaine local anaesthetic sympathetic blockade probably does not reduce pain intensity compared with placebo, and low-certainty evidence that it may not reduce pain intensity compared with ultrasound of the stellate ganglion. No effect size was reported for either comparison. There was low-certainty evidence that topical dimethyl sulfoxide may not reduce pain intensity compared with oral N-acetylcysteine, but no effect size was reported. There was low-certainty evidence that continuous bupivacaine brachial plexus block may reduce pain intensity compared with continuous bupivacaine stellate ganglion block, but no effect size was reported. For a wide range of other commonly used interventions, the certainty in the evidence was very low and provides insufficient evidence to either support or refute their use. Comparisons with low- and very low-certainty evidence should be treated with substantial caution. We did not identify any RCT evidence for routinely used pharmacological interventions for CRPS such as tricyclic antidepressants or opioids.

AUTHORS' CONCLUSIONS

Despite a considerable increase in included evidence compared with the previous version of this overview, we identified no high-certainty evidence for the effectiveness of any therapy for CRPS. Until larger, high-quality trials are undertaken, formulating an evidence-based approach to managing CRPS will remain difficult. Current non-Cochrane systematic reviews of interventions for CRPS are of low methodological quality and should not be relied upon to provide an accurate and comprehensive summary of the evidence.

Alpha-2 macroglobulin for the treatment of neuroma pain in the stump of a below-knee amputee patient

This case report describes the successful treatment of neuroma pain in the setting of below knee amputations using alpha-2-macroglobulin (A2M). A 34-year-old female patient presented with 9 months of stump pain despite conservative treatment. The exam revealed persistent pain through rest periods and weight-bearing status during therapy. Ultrasound showed neuroma formation with neovascularization. The patient underwent two A2M hydrodissection treatments, 2 weeks apart. The patient reported significant pain relief. Ultrasound showed decreases in neovascularization and cross-sectional area of the neuroma. The patient was able to ambulate pain-free for 2 years and reported no pain since. A2M may be a treatment for patients with neuroma pain in the setting of amputations.

Platelet Rich Plasma and Platelet-Related Products in the Treatment of Radiculopathy-A Systematic Review of the Literature

Back pain with radicular symptoms is associated with detrimental physical and emotional functioning and economic burden. Conservative treatments including physical, pharmacologic and injection therapy may not provide clinically significant or long-standing relief. Regenerative medicine research including Platelet rich plasma (PRP), Platelet lysate (PL) or Plasma rich in growth factors (PRGF) continues to develop, however evidence appraisal for treatment of radicular pain remains lacking. Thus, we performed a systematic review to evaluate the effectiveness of epidural steroid injections containing PRP or related products to treat radicular pain. Embase, PubMed/MEDLINE, Cochrane Central Register of Controlled Trials (CENTRAL), and Google Scholar databases were queried. Twelve studies were included in qualitative analysis, consisting of three randomized controlled trials and nine observational studies. The primary outcome was pain intensity, and secondary outcomes included functional improvement, anatomical changes on advanced imaging, and adverse events. All studies identified improved pain intensity and functional outcomes after epidural injection of PRP, PRGF and/or PL. Similar or longer lasting pain relief was noted in the PRP cohort compared to the cohort receiving epidural steroid injections with effects lasting up to 12-24 months. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) analysis revealed a very-low certainty of evidence due to risk of bias, indirectness, and imprecision.