A Systematic Review of the Diagnostic Methods of Small Fiber Neuropathies in Rehabilitation

Electroacupuncture Inhibits NLRP3-Mediated Microglial Pyroptosis to Ameliorate Chronic Neuropathic Pain in Rats

Background

Patients with neuropathic pain (NP), caused by injury or disease of the somatosensory nervous system, usually suffer from severe pain. Our previous studies revealed that electroacupuncture (EA) stimulation could effectively improve NP. However, the underlying mechanisms of EA have not been fully clarified. This study aimed to investigate the specific mechanisms of EA in alleviating NP, focusing on the pyroptosis.

Materials and Methods

Chronic Constriction Injury (CCI) model was established on the male Sprague-Dawley rats. CCI rats were treated with EA at acupoints GV20 and ST36 or/with the NOD-like receptor protein 3 (NLRP3) antagonist MCC950. EA treatment was administered for successive 14 days 7 days after the CCI surgery. The mechanical withdrawal threshold (MWT) and paw withdrawal latency (PWL) were performed during the experiment. At the end of the experiment, spinal cord segments and serum of rats were collected, ELISA detected the expression of inflammatory factors, immunofluorescence detected the microglia and neuron cells with pyroptosis biomarkers, and Western blot detected the NLRP3 pathway.

Results

EA treatment significantly alleviated pain hypersensitivity by increasing the MWT and PWL. Moreover, EA reduced levels of pro-inflammatory cytokines IL-1β and TNF-α in the spinal tissue. Mechanistically, the pyroptosis-related proteins, including NLRP3, N-GSDMD, Cleaved Caspase-1, IL-18 as well as IL-1β were downregulated by EA, indicating that EA attenuated the pyroptosis phenotype in NP rats. In particular, EA reduced the co-expression of NLRP3, Caspase-1 and N-GSDMD in microglia rather than in neuronal or astrocytic cells within the spinal cord of CCI rats. Pharmacological inhibition of NLRP3 inflammasome by MCC950 alleviates CCI-induced pain hypersensitivity while blocking EA's effect on anti-pyroptosis in CCI rats.

Conclusion

These findings demonstrate the EA ameliorates the neuroinflammation and pyroptosis to relieve chronic NP by suppressing NLRP3 inflammasome activation in microglia. EA may serve as a viable treatment therapy for chronic NP.

Post-COVID-19 Small Fiber Neuropathy as a New Emerging Quality of Life-Threatening Disease: A Systematic Review

Post-acute sequelae of COVID-19 (PASC) syndrome is considered an emergent and diffuse multidisciplinary problem. Compelling evidence suggests that COVID-19 increases symptoms of pre-existent small fiber neuropathy (SFN) and might trigger de novo onset of SFN. In this systematic review, for the first time, we provide a comprehensive overview of the clinical and diagnostic features of PASC-SFN, including the accompanying disorders, disease evolution, and possible treatments, described in the recent literature. Following infection, many patients reported a wide range of symptoms and complications, not self-limiting and independent from previous infection severity. SFN begins more frequently with distal limb burning pain and numbness, which accompany other dysautonomia, cognitive, visual, and osteoarticular disorders involving multiple organ systems. In an initial diagnostic suspicion, some tests might be useful as complementary examinations, such as nerve quantitative sensory testing, electromyography, and optic nerve tomography. Otherwise, definite diagnosis is reached with skin biopsy as the gold standard, along with corneal in vivo microscopy when ocular discomfort is present. Being a long-term condition, multiple and dissimilar symptomatic and disease-modifying drugs were employed for the treatment of this condition with the achievement of partial results, including steroids, pregabalin, gabapentin, duloxetine, vitamins, homotaurine and phosphatidylserine, alpha lipoic acid, immunosuppressants, and intravenous immunoglobulin therapy. PASC-SFN is a complex emerging disease and extremely challenging for physicians. At present, the only feasible management of PASC-SFN is represented by a multidisciplinary tailored approach, with future definitive protocols for diagnosis and treatment deemed essential.

Efficacy and Safety of Ultrasound-Guided Pulsed Radiofrequency Therapy of Stellate Ganglion on Refractory Painful Diabetic Peripheral Neuropathy

Background

The best tool for the management of pain associated with distal symmetric peripheral neuropathy (DSPN) is a matter of debate. Therefore, the study aimed to explore whether ultrasound-guided pulsed radiofrequency (PRF) therapy of the stellate ganglion (SG) in type 2 diabetes mellitus (T2DM) patients with painful DSPN could decrease pain severity and the need for analgesics.

Methods

Fifty-six T2DM patients with refractory painful DSPN were enrolled in this study, who then received bilateral ultrasound-guided PRF therapy of SG. The patients completed visual analog scale (VAS), simplified McGill pain questionnaire (SF-MPQ), Toronto clinical score system (TCSS), sleep duration at night (SDN), pain disability index (PDI), Karnofsky performance status (KPS), and depression screening scale (PHQ-9). After procedures, the degree of perceived pain relief, numbness relief and chills relief of the patients, and side effects were assessed. All patients underwent evaluation after the last procedure at 1, 4, 12 and 24-week follow-up periods.

Results

The postoperative VAS, SF-MPQ, TCSS, PDI and PHQ-9 scores were significantly lower, while the KPS values higher than the preoperative (P<0.05). The postoperative SDN was longer than the preoperative (P<0.05). The degree of perceived pain relief, chills relief, and numbness relief at 4, 12, and 24 weeks were lower than that at 1 week after the procedures (P<0.05). The postoperative rates of administration of analgesic were lower than those of preoperative period (P<0.05). The significant effective rates at 1, 4, 12, and 24 weeks after the procedure were 67.86%, 42.86%, 21.43%, and 17.86% and the total effective rates were 89.29%, 71.43%, 46.43%, and 32.14%. No serious complication was observed.

Conclusion

Ultrasound-guided stellate ganglion PRF therapy can effectively relieve pain and improve the quality of life in T2DM patients with refractory painful DSPN.

Small Fiber Neuropathy Associated with Post-COVID-19 and Post-COVID-19 Vaccination Arthritis: A Rare Post-Infective Syndrome or a New-Onset Disease?

Post-COVID-19 (PC) and post-COVID-19 vaccination (PCV) syndromes are considered emergent multidisciplinary disorders. PC/PCV small fiber neuropathy (SFN) was rarely described and its association with undifferentiated arthritis (UA) was never defined. We aimed to evaluate PC/PCV-UA associated with the recent onset of severe lower limb paresthesia, compare SFN positive (+) to negative (-) patients, and evaluate changes in biomarkers in SFN+ during treatments. Nineteen PC/PCV-UA-patients with possible SFN underwent skin biopsy at the Usl Tuscany Center (Florence) early arthritis outpatient clinic from September 2021 to March 2024. Eight selected SFN+ were compared to ten SFN- patients. In SFN+ patients, baseline joint ultrasound (US), electromyography (EMG), optical coherence tomography (OCT), and skin biopsy were repeated at six months. Moreover, SFN+ patients were clinically assessed by a 0-10 numeric rating scale for neurological symptoms and DAS28/ESR up to 12 months follow-up. SFN+ patients showed a lower intraepidermal nerve fiber density at histopathological examination of skin biopsies and a higher frequency of OCT and EMG abnormalities in comparison to SFN- patients. In SFN+ patients, US and DAS28/ESR significantly improved, while intraepidermal nerve fiber density did not significantly change at the six-month follow-up. Fatigue, motor impairment, burning pain, brain fog, and sensitivity disorders decreased at long-term follow-up (12 months).

Patient Outcomes After Peripheral Nerve Injury Depend on Bimanual Dexterity and Preserved Use of the Affected Hand

BACKGROUND

Little is known about how peripheral nerve injury affects human performance, behavior, and life. Hand use choices are important for rehabilitation after unilateral impairment, but rarely measured, and are not changed by the normal course of rehabilitation and daily life.

OBJECTIVE

To identify the relationship between hand use (L/R choices), motor performance, and patient-centered outcomes.

METHODS

Participants (n = 48) with unilateral peripheral nerve injury were assessed for hand use via Block Building Task, Motor Activity Log, and Edinburgh Handedness Inventory; dexterity (separately for each hand) via Nine-Hole Peg Test, Jebsen Taylor Hand Function Test, and a precision drawing task; patient-centered outcomes via surveys of disability, activity participation, and health-related quality of life; and injury-related factors including injury cause and affected nerve. Factor Analysis of Mixed Data was used to explore relationships between these variables. The data were analyzed under 2 approaches: comparing dominant hand (DH) versus non-dominant hand (NH), or affected versus unaffected hand.

RESULTS

The data were best explained by 5 dimensions. Good patient outcomes were associated with NH performance, DH performance (separately and secondarily to NH performance), and preserved function and use of the affected hand; whereas poor patient outcomes were associated with preserved but unused function of the affected hand.

CONCLUSION

After unilateral peripheral nerve injury, hand function, hand usage, and patient life arise from a complex interaction of many factors. To optimize rehabilitation after unilateral impairment, new rehabilitation methods are needed to promote performance and use with the NH, as well as the injured hand.

Exercise intervention for the management of chemotherapy-induced peripheral neuropathy: a systematic review and network meta-analysis

Purpose

Although exercise is recommended for cancer survivors with chemotherapy-induced peripheral neuropathy (CIPN), the effective types of exercise for preventing and treating CIPN remain unclear. This systematic review and network meta-analysis (NMA) aimed to evaluate the comparative effects of exercise on CIPN.

Methods

We included relevant randomized controlled trials (RCTs) identified in a 2019 systematic review that evaluated the effects of exercise on CIPN and conducted an additional search for RCTs published until 2023. We evaluated the risk of bias for each RCT; the comparative effectiveness of exercise on patient-reported quality of life (QOL) through an NMA; and the effectiveness of exercise on QOL scores, patient-reported CIPN symptoms, and pain through additional meta-analyses.

Results

Twelve studies (exercise, n = 540; control, n = 527) comparing 8 exercise interventions were included in the analysis. All studies were determined to have a high risk of bias. The meta-analyses showed significantly improved QOL [standard mean differences (SMD) 0.45; 95% confidence interval (CI) = 0.12 to 0.78] and CIPN symptoms (SMD 0.46; 95% CI = 0.11 to 0.82). No severe adverse events were reported. Pain tended to improve with exercise (SMD 0.84; 95% CI = -0.11 to 1.80). An NMA suggested that the interventions of a combination of balance and strength training showed a significant improvement in QOL scores compared to the control.

Conclusion

Exercise interventions may be beneficial for improving QOL and CIPN symptoms. High-quality large clinical trials and data are needed to conclude that exercise is beneficial and safe.

Netazepide, an Antagonist of Cholecystokinin Type 2 Receptor, Prevents Vincristine-Induced Sensory Neuropathy in Mice

Among the vinca-alkaloid class, vincristine is a potent chemotherapeutic agent with significant neurotoxic effects and is employed to address a wide spectrum of cancer types. Recently, the therapeutic potential of the cholecystokinin type 2 receptor (CCK2R) as a target for vincristine-induced peripheral neuropathy (VIPN) was demonstrated. In this study, the impact of preventive CCK2R blockade using netazepide (Trio Medicines Ltd., London, UK) was investigated in a mouse model of vincristine-induced peripheral neuropathy. Netazepide is a highly selective CCK2R antagonist under development for the treatment of patients with gastric neuroendocrine tumors caused by hypergastrinemia secondary to chronic autoimmune atrophic gastritis. Vincristine-induced peripheral neuropathy was induced by intraperitoneal injections of vincristine at 100 µg/kg/d for 7 days (D0 to D7). Netazepide (2 mg/kg/d or 5 mg/kg/d, per os) was administered one day before vincristine treatment until D7. Vincristine induced a high tactile allodynia from D1 to D7. VIPN was characterized by dorsal root ganglion neuron (DRG) and intraepidermal nerve fiber (IENF) loss, and enlargement and loss of myelinated axons in the sciatic nerve. Netazepide completely prevented the painful symptoms and nerve injuries induced by vincristine. In conclusion, the fact that netazepide protected against vincristine-induced peripheral neuropathy in a mouse model strongly supports the assessment of its therapeutic potential in patients receiving such chemotherapy.

Sudomotor dysfunction in diabetic peripheral neuropathy (DPN) and its testing modalities: A literature review

Long term consequences of diabetes mellitus (DM) may include multi-organ complications such as retinopathy, cardiovascular disease, neuronal, and kidney damage. One of the most prevalent complication is diabetic peripheral neuropathy (DPN), occurring in half of all diabetics, and is the main cause of disability globally with profound impact on a patient's quality of life. Small fiber neuropathy (SFN) can develop in the pre-diabetes stage preceding large fiber damage in DPN. Asymptomatic SFN is difficult to diagnose in early stages, with sudomotor dysfunction considered one of the earliest manifestations of autonomic neuropathy. Early detection is crucial as it can prevent potential cardiovascular events. Although punch skin biopsy is the gold-standard method for SFN diagnosis, implementation as routine screening is hindered due to its invasive, impractical, and time-consuming nature. Other sudomotor testing modalities, most of which evaluate the postganglionic cholinergic sympathetic nervous system, have been developed with varying sensitivity and specificity for SFN diagnosis. Here, we provide an overview on the general mechanism of DPN, the importance of sudomotor assessment for early detection of autonomic dysfunction in DPN, the benefits and disadvantages of current testing modalities, factors that may affect testing, and the importance of future discoveries on sudomotor testing for successful DPN diagnosis.

Comparison of Novel Wide-Field In Vivo Corneal Confocal Microscopy With Skin Biopsy for Assessing Peripheral Neuropathy in Type 2 Diabetes

Diabetic peripheral neuropathy (DPN) is a serious complication of diabetes, where skin biopsy assessing intraepidermal nerve fiber density (IENFD) plays an important diagnostic role. In vivo confocal microscopy (IVCM) of the corneal subbasal nerve plexus has been proposed as a noninvasive diagnostic modality for DPN. Direct comparisons of skin biopsy and IVCM in controlled cohorts are lacking, as IVCM relies on subjective selection of images depicting only 0.2% of the nerve plexus. We compared these diagnostic modalities in a fixed-age cohort of 41 participants with type 2 diabetes and 36 healthy participants using machine algorithms to create wide-field image mosaics and quantify nerves in an area 37 times the size of prior studies to avoid human bias. In the same participants, and at the same time point, no correlation between IENFD and corneal nerve density was found. Corneal nerve density did not correlate with clinical measures of DPN, including neuropathy symptom and disability scores, nerve conduction studies, or quantitative sensory tests. Our findings indicate that corneal and intraepidermal nerves likely mirror different aspects of nerve degeneration, where only intraepidermal nerves appear to reflect the clinical status of DPN, suggesting that scrutiny is warranted concerning methodologies of studies using corneal nerves to assess DPN.

ARTICLE HIGHLIGHTS

Comparison of intraepidermal nerve fiber density with automated wide-field corneal nerve fiber density in participants with type 2 diabetes revealed no correlation between these parameters. Intraepidermal and corneal nerve fibers both detected neurodegeneration in type 2 diabetes, but only intraepidermal nerve fibers were associated with clinical measures of diabetic peripheral neuropathy. A lack of association of corneal nerves with peripheral neuropathy measures suggests that corneal nerve fibers may be a poor biomarker for diabetic peripheral neuropathy.

Assessment of intraepidermal nerve fiber density and neurophysiological studies in patients with idiopathic polyneuropathy

Background

Idiopathic polyneuropathy is an asymmetrical, length-dependent neuropathy in which neurophysiology demonstrates axonal damage involving large fibers, along with insidious onset and slow progression over 6 months, with no identified etiology in spite of thorough investigations. This study aimed to evaluate the diagnostic role of clinical, electrophysiological, and histopathological studies in patients with idiopathic polyneuropathy.

Methods

Case–control study included 20 patients with clinical and neurophysiological evidence of sensory or sensory–motor neuropathy with no apparent etiology after laboratory investigation were recruited from 127 patients with sensory–motor neuropathy of unknown etiology (the patients group). Twenty apparently healthy individuals, age- and sex-matched, with no neuropathy symptoms (the control group), were recruited from the Neurology Clinic of Al-Azhar University, Assuit.

Results

Age of onset of patients with idiopathic polyneuropathy (44–70) years, duration of illness (1–6) years, 60% had painful neuropathy, diagnostic neuropathic pain questioner (DN4 score) (5–7), abnormal pin brick (80%), abnormal vibration (90%), abnormal fine touch (75%), distal weakness (70%), and lost ankle reflex (90%). In the control group, there were substantial differences with respect to prolonged latency, diminished sympathetic skin response amplitude, and significant intraepidermal nerve fiber density reduction in skin biopsy cases. In diagnosing idiopathic polyneuropathy, the specificity and sensitivity of sympathetic skin response were (80–86)% and (81–89.5)%, respectively, whereas those of diminished intraepidermal nerve fiber density were (92.5%) and (97.5%), respectively.

Conclusion

The assessment of intraepidermal nerve fiber density had an important good diagnostic role in cases presented with polyneuropathy.

DTI and MTR Measures of Nerve Fiber Integrity in Pediatric Patients With Ankle Injury

Acute peripheral nerve injury can lead to chronic neuropathic pain. Having a standardized, non-invasive method to evaluate pathological changes in a nerve following nerve injury would help with diagnostic and therapeutic assessments or interventions. The accurate evaluation of nerve fiber integrity after injury may provide insight into the extent of pathology and a patient's level of self-reported pain. The aim of this investigation was to evaluate the extent to which peripheral nerve integrity could be evaluated in an acute ankle injury cohort and how markers of nerve fiber integrity correlate with self-reported pain levels in afferent nerves. We recruited 39 pediatric participants with clinically defined neuropathic pain within 3 months of an ankle injury and 16 healthy controls. Participants underwent peripheral nerve MRI using diffusion tensor (DTI) and magnetization transfer imaging (MTI) of their injured and non-injured ankles. The imaging window was focused on the branching point of the sciatic nerve into the tibial and fibular division. Each participant completed the Pain Detection Questionnaire (PDQ). Findings demonstrated group differences in DTI and MTI in the sciatic, tibial and fibular nerve in the injured ankle relative to healthy control and contralateral non-injured nerve fibers. Only AD and RD from the injured fibular nerve correlated with PDQ scores which coincides with the inversion-dominant nature of this particular ankle injuruy cohort. Exploratory analyses highlight the potential remodeling stages of nerve injury from neuropathic pain. Future research should emphasize sub-acute time frames of injury to capture post-injury inflammation and nerve fiber recovery.

Intraepidermal Nerve Fiber Density as Measured by Skin Punch Biopsy as a Marker for Small Fiber Neuropathy: Application in Patients with Fibromyalgia

Small fiber neuropathy (SFN) is a type of peripheral neuropathy that occurs from damage to the small A-delta and C nerve fibers that results in the clinical condition known as SFN. This pathology may be the result of metabolic, toxic, immune-mediated, and/or genetic factors. Small fiber symptoms can be variable and inconsistent and therefore require an objective biomarker confirmation. Small fiber dysfunction is not typically captured by diagnostic tests for large-fiber neuropathy (nerve conduction and electromyographic study). Therefore, skin biopsies stained with PGP 9.5 are the universally recommended objective test for SFN, with quantitative sensory tests, autonomic function testing, and corneal confocal imaging as secondary or adjunctive choices. Fibromyalgia (FM) is a heterogenous syndrome that has many symptoms that overlap with those found in SFN. A growing body of research has shown approximately 40-60% of patients carrying a diagnosis of FM have evidence of SFN on skin punch biopsy. There is currently no clearly defined phenotype in FM at this time to suggest whom may or may not have SFN, though research suggests it may correlate with severe cases. The skin punch biopsy provides an objective tool for use in quantifying small fiber pathology in FM. Skin punch biopsy may also be repeated for surveillance of the disease as well as measuring response to treatments. Evaluation of SFN in FM allows for better classification of FM and guidance for patient care as well as validation for their symptoms, leading to better use of resources and outcomes.

Peripheral Neuropathy under Oncologic Therapies: A Literature Review on Pathogenetic Mechanisms

Peripheral neurologic complications are frequent adverse events during oncologic treatments and often lead to dose reduction, administration delays with time elongation of the therapeutic plan and, not least, worsening of patients’ quality of life. Experience skills are required to recognize symptoms and clinical evidences and the collaboration between different health professionals, in particular oncologists and hospital pharmacists, grants a correct management of this undesirable occurrence. Some classes of drugs (platinates, vinca alkaloids, taxanes) typically develop this kind of side effect, but the genesis of chemotherapy-induced peripheral neuropathy is not linked to a single mechanism. This paper aims from one side at summarizing and explaining all the scattering mechanisms of chemotherapy-induced peripheral neuropathy through a detailed literature revision, on the other side at finding new approaches to possible treatments, in order to facilitate the collaboration between oncologists, hematologists and hospital pharmacists.

Contribution of Skin Biopsy in Peripheral Neuropathies

In the last three decades the study of cutaneous innervation through 3 mm-punch-biopsy has provided an important contribution to the knowledge of small fiber somatic and autonomic neuropathies but also of large fiber neuropathies. Skin biopsy is a minimally invasive technique with the advantage, compared to sural nerve biopsy, of being suitable to be applied to any site in our body, of being repeatable over time, of allowing the identification of each population of nerve fiber through its target. In patients with symptoms and signs of small fiber neuropathy the assessment of IntraEpidermal Nerve Fiber density is the gold standard to confirm the diagnosis while the quantification of sudomotor, pilomotor, and vasomotor nerve fibers allows to evaluate and characterize the autonomic involvement. All these parameters can be re-evaluated over time to monitor the disease process and to evaluate the effectiveness of the treatments. Myelinated fibers and their receptors can also be evaluated to detect a “dying back” neuropathy early when nerve conduction study is still normal. Furthermore, the morphometry of dermal myelinated fibers has provided new insight into pathophysiological mechanisms of different types of inherited and acquired large fibers neuropathies. In genetic neuropathies skin biopsy has become a surrogate for sural nerve biopsy, no longer necessary in the diagnostic process, to study genotype–phenotype correlations.

A Systematic Review of Pharmacologic and Rehabilitative Treatment of Small Fiber Neuropathies

The aim of this systematic review is to guide the physician in defining the pharmacologic and rehabilitative therapeutic approaches for adopting the best strategies described in the current literature. The search was conducted in PubMed, EMBASE, Cochrane Library and Web of Science to identify the treatment of small fiber neuropathies. Two reviewers independently reviewed and came to a consensus on which articles met inclusion/exclusion criteria. The authors excluded the duplicates, animal studies and included the English articles in which the treatment of patients with small fiber neuropathies was described. The search identified a total of 975 articles with the keywords “small fiber neuropathy” AND “rehabilitation” OR “therapy” OR “treatment”. Seventy-eight selected full-text were analyzed by the reviewers. Forty-two publications met the inclusion criteria and were included in the systematic review to describe the rehabilitative and pharmacologic treatment of small fiber neuropathies. Despite the range of different protocols of treatment for small fiber neuropathy, other robust trials are needed. In addition, always different therapeutic approaches are used; a unique protocol could be important for the clinicians. More research is needed to build evidence for the best strategy and to delineate a definitive therapeutic protocol.