Characterization of neuromas in peripheral nerves and their effects on heterotopic bone formation

Regulatory T cell-derived enkephalin imparts pregnancy-induced analgesia

T cells have emerged as sex-dependent orchestrators of pain chronification but the sexually dimorphic mechanisms by which T cells control pain sensitivity is not resolved. Here, we demonstrate an influence of regulatory T cells (Tregs) on pain processing that is distinct from their canonical functions of immune regulation and tissue repair. Specifically, meningeal Tregs (mTregs) express the endogenous opioid, enkephalin, and mTreg-derived enkephalin exerts an antinociceptive action through a presynaptic opioid receptor signaling mechanism that is dispensable for immunosuppression. mTregs are both necessary and sufficient for suppressing mechanical pain sensitivity in female but not male mice. Notably, the mTreg modulation of pain thresholds depends on sex-hormones and expansion of enkephalinergic mTregs during gestation imparts a remarkable pregnancy-induced analgesia in a pre-existing, chronic, unremitting neuropathic pain model. These results uncover a fundamental sex-specific, pregnancy-pronounced, and immunologically-derived endogenous opioid circuit for nociceptive regulation with critical implications for pain biology and maternal health.

Biology and pathophysiology of symptomatic neuromas

ABSTRACT

Neuromas are a substantial cause of morbidity and reduction in quality of life. This is not only caused by a disruption in motor and sensory function from the underlying nerve injury but also by the debilitating effects of neuropathic pain resulting from symptomatic neuromas. A wide range of surgical and therapeutic modalities have been introduced to mitigate this pain. Nevertheless, no single treatment option has been successful in completely resolving the associated constellation of symptoms. While certain novel surgical techniques have shown promising results in reducing neuroma-derived and phantom limb pain, their effectiveness and the exact mechanism behind their pain-relieving capacities have not yet been defined. Furthermore, surgery has inherent risks, may not be suitable for many patients, and may yet still fail to relieve pain. Therefore, there remains a great clinical need for additional therapeutic modalities to further improve treatment for patients with devastating injuries that lead to symptomatic neuromas. However, the molecular mechanisms and genetic contributions behind the regulatory programs that drive neuroma formation-as well as the resulting neuropathic pain-remain incompletely understood. Here, we review the histopathological features of symptomatic neuromas, our current understanding of the mechanisms that favor neuroma formation, and the putative contributory signals and regulatory programs that facilitate somatic pain, including neurotrophic factors, neuroinflammatory peptides, cytokines, along with transient receptor potential, and ionotropic channels that suggest possible approaches and innovations to identify novel clinical therapeutics.

Stem cells and pain

Pain can be defined as an unpleasant sensory and emotional experience caused by either actual or potential tissue damage or even resemble that unpleasant experience. For years, science has sought to find treatment alternatives, with minimal side effects, to relieve pain. However, the currently available pharmacological options on the market show significant adverse events. Therefore, the search for a safer and highly efficient analgesic treatment has become a priority. Stem cells (SCs) are non-specialized cells with a high capacity for replication, self-renewal, and a wide range of differentiation possibilities. In this review, we provide evidence that the immune and neuromodulatory properties of SCs can be a valuable tool in the search for ideal treatment strategies for different types of pain. With the advantage of multiple administration routes and dosages, therapies based on SCs for pain relief have demonstrated meaningful results with few downsides. Nonetheless, there are still more questions than answers when it comes to the mechanisms and pathways of pain targeted by SCs. Thus, this is an evolving field that merits further investigation towards the development of SC-based analgesic therapies, and this review will approach all of these aspects.

CatWalk XT gait parameters: a review of reported parameters in pre-clinical studies of multiple central nervous system and peripheral nervous system disease models

Automated gait assessment tests are used in studies of disorders characterized by gait impairment. CatWalk XT is one of the first commercially available automated systems for analyzing the gait of rodents and is currently the most used system in peer-reviewed publications. This automated gait analysis system can generate a large number of gait parameters. However, this creates a new challenge in selecting relevant parameters that describe the changes within a particular disease model. Here, for the first time, we performed a multi-disorder review on published CatWalk XT data. We identify commonly reported CatWalk XT gait parameters derived from 91 peer-reviewed experimental studies in mice, covering six disorders of the central nervous system (CNS) and peripheral nervous system (PNS). The disorders modeled in mice were traumatic brain injury (TBI), stroke, sciatic nerve injury (SNI), spinal cord injury (SCI), Parkinson's disease (PD), and ataxia. Our review consisted of parameter selection, clustering, categorization, statistical evaluation, and data visualization. It suggests that certain gait parameters serve as potential indicators of gait dysfunction across multiple disease models, while others are specific to particular models. The findings also suggest that the more site-specific the injury is, the fewer parameters are reported to characterize its gait abnormalities. This study strives to present a clearly organized picture of gait parameters used in each one of the different mouse models, potentially helping novel CatWalk XT users to apply this information to similar or related mouse models they are working on.

Painful total knee arthroplasty: Infrapatellar branch of the saphenous nerve selective denervation. A case series

INTRODUCTION

Total knee arthroplasty (TKA) is a reliable and widespread solution for knee osteoarthritis treatment, but about 20% of the patients complains of persisting pain. Neuroma formation in the IPBSN (infrapatellar branch of the saphenous nerve) is an undervalued cause of persistent anterior pain after TKA. The aim of this study was to evaluate the effectiveness of the selective neuroma denervation on patients satisfaction and pain improvement.

MATHERIAL AND METHODS

Between 2014 and 2020, we evaluated 13 patients suffering from persistent anterior knee pain and numbness after TKA who underwent a surgical neurectomy of the IPBSN. After clinical assessment and diagnosis confirmation, we carried out the surgery. Short Form 12 Health (SF12), Oxford Knee Score (OKS), and Numeric Rating Scale (NRS) have been collected before and after the procedure. After the surgical treatment, the symptom's resolution and patients' satisfaction were attested by the achievement of the Minimal ClinicallyImportantDifference(MCID) of the self-administered patient-reported outcome measures (PROMs).

RESULTS

Our results showed a statistically significant improvement (p < 0.05) of patients pain perception (mean NRS improvement -4.2, SD 2.5) and overall satisfaction (with a mean increase in OKS of 14.5 points SD 9.4, and in SF12 of 6.5 points SD 4.0).

CONCLUSIONS

Hence, our study suggests that selective neuroma denervation may be an effective solution to improve the quality of life of patients who develop this complication after TKA.

Corneal Cellular and Neuroinflammatory Changes After SARS-CoV-2 Infection

PURPOSE

The purpose of this study was to evaluate corneal cellular and ultrastructural changes and to quantify the neuroinflammatory process in patients after mild severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

METHODS

Thirty patients after SARS-CoV-2 infection and 41 age-matched controls were examined. All subjects underwent in vivo confocal microscopy of the corneal cell layers and subbasal nerve fibers with the Heidelberg Retina Tomograph II. Semiautomated analysis of basal epithelial, anterior and posterior stromal keratocyte, and endothelial cell density was performed. Dendritic cell (DC) density and area were also calculated, and subbasal nerve plexus morphology was analyzed.

RESULTS

The posterior stromal keratocyte density was significantly lower in patients after SARS-CoV-2 infection ( P = 0.0006). DC density in the central cornea was significantly higher in patients after SARS-CoV-2 infection ( P = 0.0004). There was a significant difference in the DC area between the 2 groups ( P < 0.0001). Significantly altered subbasal nerve fiber morphology was detected in patients after SARS-CoV-2 infection compared with healthy volunteers ( P < 0.05).

CONCLUSIONS

Corneal cellular and ultrastructural changes demonstrated in this study suggest neuroinflammatory consequences of COVID-19 in the cornea in the absence of ophthalmoscopic alterations.

Disruption of targeted muscle reinnervation due to heterotopic ossification in an amputated lower extremity

A patient in his late 40s presented after 1-year following below knee amputation and targeted muscle reinnervation (TMR) with new prosthesis intolerance and pinpoint pain, suspicious for neuroma. X-ray confirmed fibular heterotopic ossification (HO). Operative revision identified HO encompassing a TMR construct with a large neuroma requiring excision and neuroplasty revision. Now approximately 1-year post procedure, the patient remains active, pain-free and ambulating with a prosthetic. Amputated extremities can be at risk for development of HO. Although described in literature, the pathophysiology and timeline for HO development is not well understood. Preventative measures for HO have been described, yet results remain variable. The gold standard for existing HO remains to be operative excision. Due to the unpredictable nature and debilitating presentation, risk of HO should be incorporated into patient-physician discussions. Additionally, new prosthetic intolerance absent of prior trauma should raise suspicion for possible HO development.

Role of adipose mesenchymal stem cells and secretome in peripheral nerve regeneration

The use of stem cells is a breakthrough in medical biotechnology which brings regenerative therapy into a new era. Over the past several decades, stem cells had been widely used as regenerative therapy and Mesenchymal Stem Cells (MSCs) had emerged as a promising therapeutic option. Currently stem cells are effective therapeutic agents againts several diseases due to their tissue protective and repair mechanisms. This therapeutic effect is largely due to the biomolecular properties including secretomes. Injury to peripheral nerves has significant health and economic consequences, and no surgical procedure can completely restore sensory and motor function. Stem cell therapy in peripheral nerve injury is an important future intervention to achieve the best clinical outcome improvement. Adipose mesenchymal stem cells (AdMSCs) are multipotent mesenchymal stem cells which are similar to bone marrow-derived mesenchymal stem cells (BM-MSCs). The following review aims to provide an overview of the use of AdMSCs and their secretomes in regenerating peripheral nerves.

Comparative Pathology of the Peripheral Nervous System

The peripheral nervous system (PNS) relays messages between the central nervous system (brain and spinal cord) and the body. Despite this critical role and widespread distribution, the PNS is often overlooked when investigating disease in diagnostic and experimental pathology. This review highlights key features of neuroanatomy and physiology of the somatic and autonomic PNS, and appropriate PNS sampling and processing techniques. The review considers major classes of PNS lesions including neuronopathy, axonopathy, and myelinopathy, and major categories of PNS disease including toxic, metabolic, and paraneoplastic neuropathies; infectious and inflammatory diseases; and neoplasms. This review describes a broad range of common PNS lesions and their diagnostic criteria and provides many useful references for pathologists who perform PNS evaluations as a regular or occasional task in their comparative pathology practice.