Primary erythromelalgia: a review

Nociceptor sodium channels shape subthreshold phase, upstroke, and shoulder of action potentials

Voltage-gated sodium channels (VGSCs) in the peripheral nervous system shape action potentials (APs) and thereby support the detection of sensory stimuli. Most of the nine mammalian VGSC subtypes are expressed in nociceptors, but predominantly, three are linked to several human pain syndromes: while Nav1.7 is suggested to be a (sub-)threshold channel, Nav1.8 is thought to support the fast AP upstroke. Nav1.9, as it produces large persistent currents, is attributed a role in determining the resting membrane potential. We characterized the gating of Nav1.1-Nav1.3 and Nav1.5-Nav1.9 in manual patch clamp with a focus on the AP subthreshold depolarization phase. Nav1.9 exhibited the most hyperpolarized activation, while its fast inactivation resembled the depolarized inactivation of Nav1.8. For some VGSCs (e.g., Nav1.1 and Nav1.2), a positive correlation between ramp current and window current was detected. Using a modified Hodgkin-Huxley model that accounts for the time needed for inactivation to occur, we used the acquired data to simulate two nociceptive nerve fiber types (an Aδ- and a mechano-insensitive C-nociceptor) containing VGSC conductances according to published human RNAseq data. Our simulations suggest that Nav1.9 is supporting both the AP upstroke and its shoulder. A reduced threshold for AP generation was induced by enhancing Nav1.7 conductivity or shifting its activation to more hyperpolarized potentials, as observed in Nav1.7-related pain disorders. Here, we provide a comprehensive, comparative functional characterization of VGSCs relevant in nociception and describe their gating with Hodgkin-Huxley-like models, which can serve as a tool to study their specific contributions to AP shape and sodium channel-related diseases.

Thermosensory Roles of G Protein-Coupled Receptors and Other Cellular Factors in Animals

In this review, we introduce the concept of "dual thermosensing mechanisms," highlighting the functional collaboration between G protein-coupled receptors (GPCRs) and transient receptor potential (TRP) channels that enable sophisticated cellular thermal responsiveness. GPCRs have been implicated in thermosensory processes, with recent findings identifying several candidates across species, including mammals, fruit flies, and nematodes. In many cases, these GPCRs work in conjunction with another class of thermosensors, TRP channels, offering insights into the complex mechanisms underlying thermosensory signaling. We examine how GPCRs function as thermosensors and how their signaling regulates cellular thermosensation, illustrating the complexity of thermosensory systems. Understanding these dual thermosensory mechanisms would advance our comprehension of cellular thermosensation and its regulatory pathways.

Diagnosis and initial management of children presenting with premature loss of primary teeth associated with a systemic condition: A scoping review and development of clinical aid

BACKGROUND

Premature loss of primary teeth (PLPT) can be a rare presentation of systemic medical conditions. Premature loss of primary teeth may present a diagnostic dilemma to paediatric dentists.

AIMS

To identify systemic conditions associated with PLPT and develop a clinical aid.

DESIGN

OVID Medline, Embase and Web of Science were searched up to March 2023. Citation searching of review publications occurred. Exclusion occurred for conference abstracts, absence of PLPT and absence of English-language full text.

RESULTS

Seven hundred and ninety-one publications were identified via databases and 476 by citation searching of review articles. Removal of 390 duplicates occurred. Following the exclusion of 466 records on abstract review, 411 publications were sought for retrieval, of which 142 met inclusion criteria. Thirty-one systemic conditions were identified. For 19 conditions, only one publication was identified. The majority of publications, 91% (n = 129), were case reports or series. Most publications, 44% (n = 62), were related to hypophosphatasia, and 25% (n = 35) were related to Papillon-Lefèvre. Diagnostic features were synthesised, and a clinical aid was produced by an iterative consensus approach.

CONCLUSIONS

A diverse range of systemic diseases are associated with PLPT. Evidence quality, however, is low, with most diseases having a low number of supporting cases. This clinical aid supports paediatric dentists in differential diagnosis and onward referral.

Small fiber neuropathy

Small fiber neuropathy (SFN) is a condition involving the small nerve fibers of the peripheral nervous system, specifically the thinly myelinated Aδ and unmyelinated C fibers. It is an increasingly acknowledged condition within the spectrum of neuropathic pain disorders, leading to a rise in diagnosed patients. SFN is characterized by neuropathic pain, that is often described as burning, and typically presents in the hands and feet ascending proximally. Since small nerve fibers are involved in the autonomic nervous system, SFN can also lead to autonomic dysfunction. In the clinical setting, SFN diagnosis is frequently based on the Besta Criteria, which include skin biopsy and quantitative sensory testing. For clinical trials, the ACTTION criteria are also recommended. However, the diagnostic process is often complex, prompting research towards more accessible diagnostic methods. The pathophysiology of SFN remains unclear, thereby challenging therapeutic strategies. A large variety of underlying conditions has been associated with SFN, including metabolic, immune-mediated, infectious, toxic and hereditary conditions. The discovery of genetic sodium channelopathies in SFN provides insight into its underlying mechanisms. Newly discovered mutations within these genes reveal that SFN often shows overlapping clinical presentations with other sodium channelopathies. This chapter provides an in-depth look at SFN, including its clinical features, diagnostic methods, underlying conditions and possible therapeutic strategies.

Successful Administration of Kampo Medicine and Acupuncture Treatment to Improve Erythromelalgia: A Case Report

Erythromelalgia is a rare disease characterized by a triad of recurrent burning pain, redness with pain, and hot flashes in the legs during attacks. We report the case of a 40-year-old woman who suffered from refractory erythromelalgia for 15 years and was successfully managed with Kampo medicine and acupuncture. Her pain was refractory to seven types of oral medications and intravenous lidocaine injections. Byakkokaninjinto was also administered for concomitant polydipsia in addition to acupuncture, unseiin, orengedokuto, and sokeikakketsuto. Because erythromelalgia has no established treatment, traditional Kampo medicine combined with acupuncture may help improve the quality of life of affected patients.

Erythromelalgia. Part I: Pathogenesis, clinical features, evaluation, and complications

Erythromelalgia is a rare pain disorder that is underrecognized and difficult-to-treat. It is characterized by episodes of extremity erythema and pain that can be disabling; it may be genetic, related to an underlying systemic disease, or idiopathic. Considering the prominent cutaneous features characteristic of the condition, dermatologists can play an important role in early recognition and limitation of morbidity. The first article in this 2-part continuing medical education series reviews the epidemiology, pathogenesis, clinical manifestations, evaluation, and complications.

Erythromelalgia. Part II: Differential diagnoses and management

The management of erythromelalgia is challenging and requires multidisciplinary effort. Patient education is crucial as unsafe self-administered cooling techniques can lead to significant morbidity, including acral necrosis, infection, and amputation. The goal of management is pain control, reduction of flare frequency, and prevention of complications. This text is focused on the management of erythromelalgia and several other incompletely understood and under-recognized neurovascular disorders such as red scrotum syndrome, red ear syndrome, facial flushing, and complex regional pain syndrome.

Erythromelalgia Secondary to Anti-Tumor Necrosis Factor (TNF) Alpha Therapy: A Report of Two Cases

Erythromelalgia is a rare syndrome with a generally unknown etiology. Whether primary or secondary, this condition is characterized by paroxysmal episodes of erythema, pain, and heat in the extremities. We report two cases of erythromelalgia occurring after the initiation of treatment with infliximab. The first case involves a 38-year-old patient who had been followed since August 2022 for ileocolonic Crohn's disease classified as A2L3B3 according to the Montreal classification, which was resistant to treatment and required infliximab therapy. Two months after the first infusion of infliximab, the patient developed symptoms of erythromelalgia. After ruling out other potential causes through an etiological assessment and conducting a pharmacological investigation, infliximab was considered the most likely cause. Infliximab was discontinued, and symptomatic treatment was initiated, including vascular laser sessions. The patient showed significant clinical improvement. In the second case, a 16-year-old patient with ileocolonic Crohn's disease classified as A1L3B3 according to the Montreal classification was treated with ileocecal resection and received an infusion of infliximab. Sixteen days after the second infusion, she developed clinical symptoms of erythromelalgia. The etiological assessment was inconclusive. Due to a strong suspicion of erythromelalgia secondary to tumor necrosis factor (TNF) alpha inhibitor therapy, infliximab was replaced with ustekinumab. The patient also received symptomatic treatment, and her clinical condition improved, marked by the disappearance of pain.

Erythromelalgia caused by the missense mutation p.Arg220Pro in an alternatively spliced exon of SCN9A (NaV1.7)

Erythromelalgia (EM), is a familial pain syndrome characterized by episodic 'burning' pain, warmth, and erythema. EM is caused by monoallelic variants in SCN9A, which encodes the voltage-gated sodium channel (NaV) NaV1.7. Over 25 different SCN9A mutations attributed to EM have been described to date, all identified in the SCN9A transcript utilizing exon 6N. Here we report a novel SCN9A missense variant identified in seven related individuals with stereotypic episodes of bilateral lower limb pain presenting in childhood. The variant, XM_011511617.3:c.659G>C;p.(Arg220Pro), resides in the exon 6A of SCN9A, an exon previously shown to be selectively incorporated by developmentally regulated alternative splicing. The mutation is located in the voltage-sensing S4 segment of domain I, which is important for regulating channel activation. Functional analysis showed the p.Arg220Pro mutation altered voltage-dependent activation and delayed channel inactivation, consistent with a NaV1.7 gain-of-function molecular phenotype. These results demonstrate that alternatively spliced isoforms of SCN9A should be included in all genomic testing of EM.

A case of erythromelalgia with gastrointestinal dysautonomia treated with immunoglobulin: A case report

An 18-year-old female with a history of atopic march, hyperhidrosis, and eosinophilic esophagitis was diagnosed with erythromelalgia and gastrointestinal dysautonomia secondary to presumed autoimmune small fiber neuropathy. The patient experienced significant clinical improvements after the initiation of intravenous immunoglobulin therapy, supporting an underlying autoimmune disorder.

Peripheral temperature dysregulation associated with functionally altered NaV1.8 channels

The voltage-gated sodium channel NaV1.8 is prominently expressed in the soma and axons of small-caliber sensory neurons, and pathogenic variants of the corresponding gene SCN10A are associated with peripheral pain and autonomic dysfunction. While most disease-associated SCN10A variants confer gain-of-function properties to NaV1.8, resulting in hyperexcitability of sensory neurons, a few affect afferent excitability through a loss-of-function mechanism. Using whole-exome sequencing, we here identify a rare heterozygous SCN10A missense variant resulting in alteration p.V1287I in NaV1.8 in a patient with a 15-year history of progressively worsening temperature dysregulation in the distal extremities, particularly in the feet. Further symptoms include increasingly intensifying tingling and numbness in the fingers and increased sweating. To assess the impact of p.V1287I on channel function, we performed voltage-clamp recordings demonstrating that the alteration confers loss- and gain-of-function characteristics to NaV1.8 characterized by a right-shifted voltage dependence of channel activation and inactivation. Current-clamp recordings from transfected mouse dorsal root ganglion neurons further revealed that NaV1.8-V1287I channels broaden the action potentials of sensory neurons and increase their firing rates in response to depolarizing current stimulations, indicating a gain-of-function mechanism of the variant at the cellular level in a heterozygous setting. The data support the hypothesis that the properties of NaV1.8 p.V1287I are causative for the patient's symptoms and that nonpainful peripheral paresthesias should be considered part of the clinical spectrum of NaV1.8-associated disorders.

Part II: Cutaneous manifestations of peripheral vascular disease

In this Part 2 of a 2-part continuing medical education series, we review the epidemiology of peripheral vascular disease, its association with cutaneous symptoms, and the diagnosis and evaluation of cutaneous features of vascular disorders. As peripheral vascular disease becomes more prevalent globally, it is essential for dermatologists to become competent at accurately recognizing and diagnosing cutaneous manifestations and directing individuals to receive appropriate care and treatment.

Clinical Challenges in Primary Erythromelalgia: a Real-Life Experience from a Single Center and a Diagnostic-Therapeutic Flow-Chart Proposal

INTRODUCTION

Primary erythromelalgia (EM) is a rare clinical syndrome characterized by recurrent erythema, burning pain and warmth of the extremities. The symptoms greatly compromise the patients' quality of life leading to severe disability. SCN9A mutations can be the cause of the disease. Dermatologists are often the specialists these patients turn to for assistance.

OBJECTIVES

To describe the demographic and clinical characteristics of patients with primary EM, to assess the presence and mutation types in the SCN9A gene, to evaluate the effectiveness of several therapeutic approaches, and to propose a diagnostic algorithm with therapeutic implications.

METHODS

A monocentric retrospective study using the database of patients with a discharge diagnosis of primary EM of our Center. Demographic, clinical, instrumental and laboratory data of patients were reviewed.

RESULTS

Eleven female patients (age range 16 to 57) were selected. All patients were affected in both the lower and upper extremities. Follow-up ranged from 2 to 9 years. Four patients had four different heterozygous variants of the SCN9A gene. Two patients, although genetically negative, had a suggestive family history. A variety of medications were tried in all our patients to alleviate symptoms, but their efficacy was variable, partial and/or transitory. The most effective therapies were antihistamines, venlafaxine, and mexiletine.

CONCLUSIONS

The diagnosis and treatment of EM remain challenging. Patients with this condition display a wide spectrum of clinical manifestations and severity, as well as a paucity of resources and structures to support them. Mutations in the SCN9A gene are not always detected.

Cyclosporine-induced erythromelalgia

Erythromelalgia is a rare syndrome characterised by recurrent erythema, heat and burning pain in the extremities. There are two types: primary (genetic) and secondary (toxic, drug-related or associated with other diseases). We report a 42-year-old woman who developed erythromelalgia after taking cyclosporine for myasthenia gravis. Although exact mechanism for this rare adverse effect is unclear, it is reversible, and so clinicians should be aware of the association . Additional use of corticosteroids could aggravate cyclosporine's toxic effects.

Case report: Spinal cord stimulation in the treatment of pediatric erythromelalgia

Introduction

In children, erythromelalgia is a rare chronic pain syndrome characterized by erythema, severe burning pain, and itching of affected feet. Unfortunately, there is no definitive therapy available currently.

Case report

Here, we report a case of primary erythromelalgia and the treatment response in a 10-year-old boy, whose genetic findings for mutations in the SCN9A gene were positive and skin biopsy results were diagnosed as small fiber neuropathy, while he has suffered from excruciating burning pain, itching, erythema, and recurrent infections over the past 3 years. He did not respond well to conventional treatment, and the only way to receive minimal relief was to immerse his feet in ice water. After a successful trial of spinal cord stimulation (SCS), the implantable pulse generator (IPG) was successfully implanted without complications, and it proved partial response to therapy.

Conclusion

There is no specific, efficient treatment for pediatric erythromelalgia currently, but this case demonstrates neuromodulation serves as part of the multimodal regimen to treat pediatric erythromelalgia.

A Case of Autoimmune Small Fiber Neuropathy as Possible Post COVID Sequelae

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is reported to induce and augment autoimmune processes. Moreover, postinfectious effects of coronavirus disease 2019 (COVID-19) are still poorly understood and often resemble symptoms of the acute infection phase. A patient with swollen extremities was presented to the Department of Angiology at the Medical University of Vienna with complaints of muscle and joint pain, paresthesia, and arterial hypertension with intense headache. Prior to these complaints, she had been suffering from various symptoms since November 2020, following a SARS-CoV-2 infection in the same month. These included recurrent sore throat, heartburn, dizziness, and headache. Paresthesia and muscle and joint pain started in temporal relation to a human papillomavirus (HPV) vaccination. Since the patient was suffering from severe pain, intensive pain management was performed. Skin and nerve biopsies revealed autoimmune small fiber neuropathy. The patient's condition could be related to COVID-19, as her first symptoms began in temporal relation to the SARS-CoV-2 infection. Furthermore, in the disease course, antinuclear (ANA) and anti-Ro antibodies, as well as anti-cyclic citrullinated peptide (anti-CCP) antibodies, could be detected. Together with the symptoms of xerophthalmia and pharyngeal dryness, primary Sjögren's syndrome was diagnosed. In conclusion, though biopsy results could not distinguish a cause of the disease, SARS-CoV-2 infection can be discussed as a likely trigger for the patient's autoimmune reactions.

A severe case of primary erythromelalgia presenting as small fiber neuropathy with a novel SCN9A mutation

Primary erythromelalgia (PEM) is a rare condition characterized by severe burning pain, erythema, and increased temperature in the extremeties. Mutations in the Nav1.7 sodium channel encoded by the SCN9A are responsible for PEM. The pathophysiology of PEM is unclear, but the involvement of neurogenic and vasogenic mechanisms has been suggested. Here we report a case of severe PEM in a 9-year-old child with a novel SCN9A mutation and examine the distribution of nerve fibers and expression of neuropeptides in the affected skin. Gene mutation analysis revealed a novel mutation p.L951I (c.2851C>A) in the heterozygous form of the SCN9A. An immunofluorescence study showed that intraepidermal nerve fibers were decreased in the affected leg, suggesting small fiber neuropathy. There was no increase in the expression of substance P (SP) or calcitonin gene-related peptide (CGRP) in the lesional skin tissue. These findings suggest SP and CGRP do not play a major role in the pathophysiology of primary erythromelalgia.

Erythromelalgia in a patient with feet erythema and cyanosis

Erythromelalgia is a rare disease characterised by a triad of a clinical syndrome of redness, warmth and painful extremities. We present the case of a male adolescent with no prior medical history who presents to our family medicine clinic with a 3-month history of bilateral feet erythema followed by episodes of cyanosis in bilateral toes. Given his history, the findings on clinical examination, and the lack of any pathology on the diagnostic testing, the patient is diagnosed with erythromelalgia. He is then counselled on both pharmacological and non-pharmacological treatments for his condition and is discharged on non-pharmacological treatment options such as leg elevation, cooling with a fan and limiting exposure to heat. The patient is also advised to perform an annual complete blood count given the association of erythromelalgia with myeloproliferative disorders.

A Review of the Therapeutic Targeting of SCN9A and Nav1.7 for Pain Relief in Current Human Clinical Trials

Introduction

There is a great need to find alternative treatments for chronic pain which have become a healthcare problem. We discuss current therapeutic targeting Nav1.7.

Areas Covered

Nav1.7 is a sodium ion channel protein that is associated with several human pain genetic syndromes. It has been found that mutations associated with Nav1.7 lead to the loss of the ability to perceive pain in individuals that are otherwise normal. Several therapeutic interventions are presently undergoing preclinical and research using the methodology of damping Nav1.7 expressions as a methodology to decrease the sensation of pain leading to analgesia.

Expert Opinion

It is our strong belief that there is a viable future in the targeting of protein of Nav1.7 for the relief of chronic pain in humans. The review will look at the genomics associated with SCN1A and proteomic of Nav1.7 as a foundation to explain the mechanism of the therapeutic interventions targeting Nav1.7, the human disease that are associated with Nav1.7, and the current development of treatment for chronic pain whether in preclinical or clinical trials targeting Nav1.7 expressions. The development of therapeutic antagonists targeting Nav1.7 could be a viable alternative to the current treatments which have led to the opioid crisis. Therefore, Nav1.7 targeted treatment has a major clinical significance that will have positive consequences as it relates to chronic pain interventions.

[Functional vascular acrosyndromes]

Vascular acrosyndromes are characterized by sparse, uniform clinical manifestations and a variety of possible pathomechanisms. The present article focuses on the functional entities. Raynaud phenomenon is based on cold- or stress-induced vasospasms of acral arteries. It is defined by the color changes of the skin, in the typical case white-blue-red (tricolore). The long fingers are most commonly affected. The etiology is unknown, and the pathophysiology is poorly understood. A distinction is made between primary and a secondary Raynaud phenomenon. The most important underlying diseases include collagenosis, primarily systemic sclerosis, and malignancies; furthermore, medications and drugs may promote vasospasm. Treatment is aimed at preventing or breaking the vasospasm, but has been only partially effective in doing so. Acrocyanosis is a vasospastic dystonic acral disorder that results in permanent reddish-livid discoloration, especially of the hands and feet. Secondary forms occur in collagenosis, malignancies, and myelodysplastic syndromes. The etiology and pathophysiology are virtually unknown. Targeted pharmacological intervention is not possible. Unlike all other vascular acrosyndromes, erythromelalgia is characterized by hyperemia. The primary form is a genetic sodium channelopathy, while secondary forms include malignancies, connective tissue diseases, and myelodysplastic syndromes. The symptoms are often distressing and disabling. Therapy requires a multimodal approach that includes both nonpharmacological and pharmacological strategies. Close interdisciplinary collaboration is essential for the management of this disease.

Novel Therapies for the Treatment of Neuropathic Pain: Potential and Pitfalls

Neuropathic pain affects more than one million people across the globe. The quality of life of people suffering from neuropathic pain has been considerably declining due to the unavailability of appropriate therapeutics. Currently, available treatment options can only treat patients symptomatically, but they are associated with severe adverse side effects and the development of tolerance over prolonged use. In the past decade, researchers were able to gain a better understanding of the mechanisms involved in neuropathic pain; thus, continuous efforts are evident, aiming to develop novel interventions with better efficacy instead of symptomatic treatment. The current review discusses the latest interventional strategies used in the treatment and management of neuropathic pain. This review also provides insights into the present scenario of pain research, particularly various interventional techniques such as spinal cord stimulation, steroid injection, neural blockade, transcranial/epidural stimulation, deep brain stimulation, percutaneous electrical nerve stimulation, neuroablative procedures, opto/chemogenetics, gene therapy, etc. In a nutshell, most of the above techniques are at preclinical stage and facing difficulty in translation to clinical studies due to the non-availability of appropriate methodologies. Therefore, continuing research on these interventional strategies may help in the development of promising novel therapies that can improve the quality of life of patients suffering from neuropathic pain.

Life-threatening hypothermia in a child with primary erythromelalgia

Primary erythromelalgia is a rare autosomal-dominant condition due to pathogenic variant in the SCN9A gene, characterized by childhood onset of excruciating pain, redness, and warmth of acral sites. Patients often resort to ice water baths and other cooling measures to manage the discomfort. Hypothermia is a rare complication, reported only twice previously. We report a child with primary erythromelalgia due to a confirmed pathogenic variant admitted with life-threatening hypothermia. Although the overuse of cooling mechanisms may have contributed, we postulate that the SCN9A mutation may lead to thermodysregulation and make patients with primary erythromelalgia particularly susceptible to this complication.

Assessing the impact of pain-linked Nav1.7 variants: An example of two variants with no biophysical effect

Mutations in the voltage-gated sodium channel Nav1.7 are linked to human pain. The Nav1.7/N1245S variant was described before in several patients suffering from primary erythromelalgia and/or olfactory hypersensitivity. We have identified this variant in a pain patient and a patient suffering from severe and life-threatening orthostatic hypotension. In addition, we report a female patient suffering from muscle pain and carrying the Nav1.7/E1139K variant. We tested both Nav1.7 variants by whole-cell voltage-clamp recordings in HEK293 cells, revealing a slightly enhanced current density for the N1245S variant when co-expressed with the β1 subunit. This effect was counteracted by an enhanced slow inactivation. Both variants showed similar voltage dependence of activation and steady-state fast inactivation, as well as kinetics of fast inactivation, deactivation, and use-dependency compared to WT Nav1.7. Finally, homology modeling revealed that the N1245S substitution results in different intramolecular interaction partners. Taken together, these experiments do not point to a clear pathogenic effect of either the N1245S or E1139K variant and suggest they may not be solely responsible for the patients' pain symptoms. As discussed previously for other variants, investigations in heterologous expression systems may not sufficiently mimic the pathophysiological situation in pain patients, and single nucleotide variants in other genes or modulatory proteins are necessary for these specific variants to show their effect. Our findings stress that biophysical investigations of ion channel mutations need to be evaluated with care and should preferably be supplemented with studies investigating the mutations in their context, ideally in human sensory neurons.

Classical Philadelphia-negative myeloproliferative neoplasms (MPNs): A continuum of different disease entities

Classical Philadelphia-negative myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell-derived disorders characterized by uncontrolled proliferation of differentiated myeloid cells and close pathobiologic and clinical features. According to the 2016 World Health Organization (WHO) classification, MPNs include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The 2016 revision aimed in particular at strengthening the distinction between masked PV and JAK2-mutated ET, and between prefibrotic/early (pre-PMF) and overt PMF. Clinical manifestations in MPNs include constitutional symptoms, microvascular disorders, thrombosis and bleeding, splenomegaly secondary to extramedullary hematopoiesis, cytopenia-related symptoms, and progression to overt MF and acute leukemia. A dysregulation of the JAK/STAT pathway is the unifying mechanistic hallmark of MPNs, and is guided by somatic mutations in driver genes including JAK2, CALR and MPL. Additional mutations in myeloid neoplasm-associated genes have been also identified, with established prognostic relevance, particularly in PMF. Prognostication of MPN patients relies on disease-specific clinical models. The increasing knowledge of MPN biology led to the development of integrated clinical and molecular prognostic scores that allow a more refined stratification. Recently, the therapeutic landscape of MPNs has been revolutionized by the introduction of potent, selective JAK inhibitors (ruxolitinib, fedratinib), that proved effective in controlling disease-related symptoms and splenomegaly, yet leaving unmet critical needs, owing the lack of disease-modifying activity. In this review, we will deal with molecular, clinical, and therapeutic aspects of the three classical MPNs aiming at highlighting either shared characteristics, that overall define a continuum within a single disease family, and uniqueness, at the same time.

Differential Modulation of the Voltage-Gated Na+ Channel 1.6 by Peptides Derived From Fibroblast Growth Factor 14

The voltage-gated Na⁺ (Nav) channel is a primary molecular determinant of the initiation and propagation of the action potential. Despite the central role of the pore-forming α subunit in conferring this functionality, protein:protein interactions (PPI) between the α subunit and auxiliary proteins are necessary for the full physiological activity of Nav channels. In the central nervous system (CNS), one such PPI occurs between the C-terminal domain of the Nav1.6 channel and fibroblast growth factor 14 (FGF14). Given the primacy of this PPI in regulating the excitability of neurons in clinically relevant brain regions, peptides targeting the FGF14:Nav1.6 PPI interface could be of pre-clinical value. In this work, we pharmacologically evaluated peptides derived from FGF14 that correspond to residues that are at FGF14's PPI interface with the CTD of Nav1.6. These peptides, Pro-Leu-Glu-Val (PLEV) and Glu-Tyr-Tyr-Val (EYYV), which correspond to residues of the β12 sheet and β8-β9 loop of FGF14, respectively, were shown to inhibit FGF14:Nav1.6 complex assembly. In functional studies using whole-cell patch-clamp electrophysiology, PLEV and EYYV were shown to confer differential modulation of Nav1.6-mediated currents through mechanisms dependent upon the presence of FGF14. Crucially, these FGF14-dependent effects of PLEV and EYYV on Nav1.6-mediated currents were further shown to be dependent on the N-terminal domain of FGF14. Overall, these data suggest that the PLEV and EYYV peptides represent scaffolds to interrogate the Nav1.6 channel macromolecular complex in an effort to develop targeted pharmacological modulators.

High frequency dorsal column spinal cord stimulation for management of erythromelalgia

Erythromelalgia is a rare hereditary channelopathy affecting the Nav1.7 sodium channel. Patients afflicted with this condition suffer from pain in their hands and feet, with vasomotor changes including flushing and redness to the distal upper and lower extremities. Current treatment modalities for this condition include pharmacological therapies (neuropathic medications), behavioural interventions, lumbar epidural infusions with local anaesthetics and sympathetic nerve blocks. Despite these treatments, many patients may have refractory pain. In these situations, there may be a role for dorsal column spinal cord stimulation for management of their pain. Here, we present the case of a 21-year-old man with 9-year history of refractory erythromelalgia successfully treated with paresthesia-free dorsal column spinal cord stimulation.

Combination gel of 2% amitriptyline and 0.5% ketamine to treat refractory erythromelalgia pain - a case report of pain control success

Erythromelalgia (EM) is a rare autosomal dominant neuropathy characterized by the combination of severe burning pain and erythematous warm extremities. Chronic pain control is most often unsuccessful and a completely effective therapy is yet to be identified. Recent studies have reported significant improvements in pain management using a combination of amitriptyline and ketamine in a topical formulation. We describe a 1-year follow-up pain control success case of a male patient with EM, proposed for topical use of a 2% Amitriptyline and 0.5% Ketamine gel.

Combination gel of 2% amitriptyline and 0.5% ketamine to treat refractory erythromelalgia pain - a case report of pain control success

Erythromelalgia (EM) is a rare autosomal dominant neuropathy characterized by the combination of severe burning pain and erythematous warm extremities. Chronic pain control is most often unsuccessful and a completely effective therapy is yet to be identified. Recent studies have reported significant improvements in pain management using a combination of amitriptyline and ketamine in a topical formulation. We describe a 1-year follow-up pain control success case of a male patient with EM, proposed for topical use of a 2% Amitriptyline and 0.5% Ketamine gel.

A reappraisal of the presence of small or large fiber neuropathy in patients with erythromelalgia

OBJECTIVE

To assess the contribution of large and small nerve fiber alteration in erythromelalgia (EM).

METHODS

Thirty-three EM patients were included and underwent clinical evaluation based on EM severity score, DN4, and Utah Early Neuropathy Scale (UENS) score. Neurophysiological evaluation consisted in nerve conduction studies (NCS) for large nerve fibers and specific tests for small nerve fibers: electrochemical skin conductance, cold and warm detection thresholds, and laser evoked potentials. Finally, the evaluation of vascular changes was based on the presence of clinical feature of microvascular disorders and the measurement of the Toe Pressure Index (TPI).

RESULTS

While 28 patients (85%) had vascular alteration on TPI or clinical features, 23 patients (70%) had small-fiber neuropathy on neurophysiological tests, and only 10 patients (30%) had large fiber neuropathy on NCS. Regarding clinical scores, there was no difference between groups (presence or absence of large- or small-fiber neuropathy or microvascular disorder) except for a higher UENS score in patients with large fiber neuropathy.

CONCLUSION

Peripheral neuropathy, mostly involving small nerve fibers, is almost as common as microvascular changes in EM, but remains inconstant and not related to a specific neuropathic pattern or higher clinical severity.

SIGNIFICANCE

The association of neuropathic and vascular factors is not systematic in EM, this syndrome being characterized by different pathophysiological mechanisms leading to a common clinical phenotype.

Loss of SLC9A6/NHE6 impairs nociception in a mouse model of Christianson syndrome

Supplemental Digital Content is Available in the Text.

Patients diagnosed with Christianson syndrome have intellectual disability, epilepsy, ataxia, and mutism, as well as hyposensitivity to pain. In this study, we use a mouse model of Christianson syndrome to demonstrate that this pain hyposensitivity is due in part to a decrease in excitability of nociceptors.

Children diagnosed with Christianson syndrome (CS), a rare X-linked neurodevelopmental disorder characterized by intellectual disability, epilepsy, ataxia, and mutism, also suffer from hyposensitivity to pain. This places them at risk of sustaining serious injuries that often go unattended. Christianson syndrome is caused by mutations in the alkali cation/proton exchanger SLC9A6/NHE6 that regulates recycling endosomal pH homeostasis and trafficking. Yet, it remains unclear how defects in this transporter lead to altered somatosensory functions. In this study, we validated a Nhe6 knockout (KO) mouse as a model of CS and used it to identify the cellular mechanisms underlying the elevated pain tolerance observed in CS patients. Within the central nervous system, NHE6 immunolabelling is detected in a small percentage of cortical neurons involved in pain processing, including those within the primary somatosensory and the anterior cingulate cortices as well as the periaqueductal gray. Interestingly, it is expressed in a larger percentage of nociceptors. Behaviourally, Nhe6 KO mice have decreased nocifensive responses to acute noxious thermal, mechanical, and chemical (ie, capsaicin) stimuli. The reduced capsaicin sensitivity in the KO mice correlates with a decreased expression of the transient receptor potential channel TRPV1 at the plasma membrane and capsaicin-induced Ca²⁺ influx in primary cultures of nociceptors. These data indicate that NHE6 is a significant determinant of nociceptor function and pain behaviours, vital sensory processes that are impaired in CS.

Red ear syndrome in children: Review of literature and report of three cases

BACKGROUND

Red ear syndrome (RES) is a neurological syndrome that is characterized by attacks of redness and pain that is localized in the earlobe, accompanied by a burning sensation, swelling or otalgia. The exact pathophysiology of RES is not known. Several pediatric cases have been described. They show an extreme variability in clinical presentation and therapeutic response, and therefore there are numerous difficulties in the diagnostic-therapeutic approach and in the comprehension of the physiopathology. The goal of this report is to present three clinical cases of red ear syndrome in children. These cases show various characteristics that can give useful indications regarding the differential diagnosis and the pathogenetic mechanisms that are involved, particularly when they are compared with cases published in the literature.

CASE-REPORTS

We report three pediatric RES cases: 1) a boy whose condition offered a typical example of the association that occurs between migraine and RES. 2) a girl with idiopathic RES. 3) a child who suffered RES attacks that showed many similarities with trigeminal autonomic cephalalgias.

CONCLUSION

Our clinical series shows the different ways in which RES can be expressed and they support the reported scientific literature. We suggest that the different forms of RES have a common final autonomic pathogenetic mechanism that is activated by parasympathetic hyperactivity and sympathetic inhibition. The different temporal characteristics, frequency, etc. may depend on the activation of distinct physiopathological modules that are related to the pain circuits, as suggested by the modular theory which describes that groups of neurons are defined as a module, where each module is responsible for a symptom and the individual's headache is defined by the activated modules.

Chemotherapy-induced peripheral neuropathy (CIPN): current therapies and topical treatment option with high-concentration capsaicin

Cancer diagnosis and treatment are drastic events for patients and their families. Besides psychological aspects of the disease, patients are often affected by severe side effects related to the cancer itself or as a result of therapeutic interventions. Particularly, chemotherapy-induced peripheral neuropathy (CIPN) is the most prevalent neurological complication of oral or intravenous chemotherapy. The disorder may require dose reduction of chemotherapy and is accompanied by multiple symptoms with long-term functional impairment affecting quality of life (QoL), e.g., sensory and functional deteriorations as well as severe pain. Although CIPN may reverse or improve after termination of the causative chemotherapy, approximately 30–40% of patients are faced with chronicity of the symptoms. Due to the advantages in cancer diagnosis and treatments, survival rates of cancer patients rise and CIPN may occur even more frequently in the future. In this review, we summarize current recommendations of leading national and international societies regarding prevention and treatment options in CIPN. A special focus will be placed on current evidence for topical treatment of CIPN with high-dose capsaicin. Finally, an algorithm for CIPN treatment in clinical practice is provided, including both pharmacologic and non-pharmacologic modalities based on the clinical presentation.

Phosphorylation of a chronic pain mutation in the voltage-gated sodium channel Nav1.7 increases voltage sensitivity

Mutations in voltage-gated sodium channels (Navs) can cause alterations in pain sensation, such as chronic pain diseases like inherited erythromelalgia. The mutation causing inherited erythromelalgia, Nav1.7 p.I848T, is known to induce a hyperpolarized shift in the voltage dependence of activation in Nav1.7. So far, however, the mechanism to explain this increase in voltage sensitivity remains unknown. In the present study, we show that phosphorylation of the newly introduced Thr residue explains the functional change. We expressed wildtype human Nav1.7, the I848T mutant, or other mutations in HEK293T cells and performed whole-cell patch-clamp electrophysiology. As the insertion of a Thr residue potentially creates a novel phosphorylation site for Ser/Thr kinases and because Nav1.7 had been shown in Xenopus oocytes to be affected by protein kinases C and A, we used different nonselective and selective kinase inhibitors and activators to test the effect of phosphorylation on Nav1.7 in a human system. We identify protein kinase C, but not protein kinase A, to be responsible for the phosphorylation of T848 and thereby for the shift in voltage sensitivity. Introducing a negatively charged amino acid instead of the putative phosphorylation site mimics the effect on voltage gating to a lesser extent. 3D modeling using the published cryo-EM structure of human Nav1.7 showed that introduction of this negatively charged site seems to alter the interaction of this residue with the surrounding amino acids and thus to influence channel function. These results could provide new opportunities for the development of novel treatment options for patients with chronic pain.

A curious observation of passive transfer of steroid antifungal combination creams to the scrotum in patients of tinea cruris-Is this forme fruste of red scrotum syndrome?

We report 16 patients of tinea cruris who presented with an asymptomatic red scrotum due to fixed dose combination creams containing antifungal agents and topical steroids applied to the thighs as a treatment of tinea cruris. The erythema resolved upon starting appropriate treatment with single molecule antifungal creams and oral antifungal drugs in about six weeks' time in majority of cases. We propose that this clinical presentation may be akin to red scrotum syndrome (RSS). Due to its asymptomatic nature in most of the cases, we propose that this could be a forme fruste of RSS.

Extensive Lumbar Sympathetic Ganglion Block Combined With Epidural Block for Primary Erythromelalgia: A Case Report

A 19-year-old-woman experienced severe burning pain in the lower extremities with erythema and swelling. She was diagnosed with primary erythromelalgia (PE). The pain was unresponsive to medications but relieved by immersing her feet in cold water. We performed a multilevel lumbar sympathetic ganglion block (LSGB) with 5% phenol at second lumbar vertebra (L2) and third lumbar vertebra (L3), and additional fourth lumbar vertebra (L4) levels. An epidural block was intermittently combined. The pain and skin lesions dramatically improved after the procedures, and she no longer needed medications or to soak her feet in cold water. This case demonstrated that extensive LSGB may be a therapeutic option for intractable PE.

Uncoupling sodium channel dimers restores the phenotype of a pain-linked Nav 1.7 channel mutation

Background and Purpose

The voltage‐gated sodium channel Na_v1.7 is essential for adequate perception of painful stimuli. Mutations in the encoding gene, SCN9A, cause various pain syndromes in humans. The hNa_v1.7/A1632E channel mutant causes symptoms of erythromelalgia and paroxysmal extreme pain disorder (PEPD), and its main gating change is a strongly enhanced persistent current. On the basis of recently published 3D structures of voltage‐gated sodium channels, we investigated how the inactivation particle binds to the channel, how this mechanism is altered by the hNa_v1.7/A1632E mutation, and how dimerization modifies function of the pain‐linked mutation.

Experimental Approach

We applied atomistic molecular simulations to demonstrate the effect of the mutation on channel fast inactivation. Native PAGE was used to demonstrate channel dimerization, and electrophysiological measurements in HEK cells and Xenopus laevis oocytes were used to analyze the links between functional channel dimerization and impairment of fast inactivation by the hNa_v1.7/A1632E mutation.

Key Results

Enhanced persistent current through hNa_v1.7/A1632E channels was caused by impaired binding of the inactivation particle, which inhibits proper functioning of the recently proposed allosteric fast inactivation mechanism. hNa_v1.7 channels form dimers and the disease‐associated persistent current through hNa_v1.7/A1632E channels depends on their functional dimerization status: Expression of the synthetic peptide difopein, a 14‐3‐3 inhibitor known to functionally uncouple dimers, decreased hNa_v1.7/A1632E channel‐induced persistent currents.

Conclusion and Implications

Functional uncoupling of mutant hNa_v1.7/A1632E channel dimers restored their defective allosteric fast inactivation mechanism. Our findings support the concept of sodium channel dimerization and reveal its potential relevance for human pain syndromes.

Ion Channels as Therapeutic Targets for Viral Infections: Further Discoveries and Future Perspectives

Ion channels play key roles in almost all facets of cellular physiology and have emerged as key host cell factors for a multitude of viral infections. A catalogue of ion channel-blocking drugs have been shown to possess antiviral activity, some of which are in widespread human usage for ion channel-related diseases, highlighting new potential for drug repurposing. The emergence of ion channel–virus interactions has also revealed the intriguing possibility that channelopathies may explain some commonly observed virus induced pathologies. This field is rapidly evolving and an up-to-date summary of new discoveries can inform future perspectives. We herein discuss the role of ion channels during viral lifecycles, describe the recently identified ion channel drugs that can inhibit viral infections, and highlight the potential contribution of ion channels to virus-mediated disease.

Diabetic Polyneuropathy - Advances in Diagnosis and Intervention Strategies

Over half of people with diabetes mellitus develop diabetic polyneuropathy (DPN), which is a major cause of reduced quality of life due to disabling neuropathic pain, sensory loss, gait instability, fall-related injury, and foot ulceration and amputation. The latter represents a major health and economic burden, with lower limb amputation rates related to diabetes increasing in the UK. There is a need for early diagnosis of DPN so that early management strategies may be instigated, such as achieving tight glucose control and management of cardiovascular risk factors, in an attempt to slow its progression. To this end, a one-stop microvascular assessment involving a combined eye, foot and renal screening clinic has proven feasible in the UK. Unfortunately, there are currently no approved disease-modifying therapies for DPN. Some disease-modifying agents have demonstrated efficacy, but further large trials using appropriate clinical endpoints are required before these treatments can be routinely recommended. There has been emerging evidence highlighting a reduction in vitamin D levels in cases of painful DPN and the potential for vitamin D supplementation in deficient individuals to improve neuropathic pain; however, this needs to be proved in randomised clinical trials. The use of established agents for neuropathic pain in DPN is limited by poor efficacy and adverse effects, but patient stratification using methods such as pain phenotyping are being tested to determine whether this improves the outcomes of such agents in clinical studies. In addition, innovative approaches such as the topical 8% capsaicin patch, new methods of electrical stimulation and novel therapeutic targets such as NaV1.7 offer promise for the future. This article aims to discuss the challenges of diagnosing and managing DPN and to review current and emerging lifestyle interventions and therapeutic options.

Taxane-induced sensory peripheral neuropathy is associated with an SCN9A single nucleotide polymorphism in Japanese patients

Background

Sodium channels located in the dorsal root ganglion, particularly Nav1.7 and Nav1.8, encoded by SCN9A and SCN10A, respectively, act as molecular gatekeepers for pain detection. Our aim was to determine the association between TIPN and SCN9A and SCN10A polymorphisms.

Methods

Three single nucleotide polymorphisms (SNPs) in SCN9A and two in SCN10A were investigated using whole-genome genotyping data from 186 Japanese breast or ovarian cancer patients classified into two groups as follows: cases that developed taxane-induced grade 2–3 neuropathy (N = 108) and controls (N = 78) with grade 0–1 neuropathy. Multiple logistic regression analyses were conducted to evaluate associations between TIPN and SNP genotypes.

Results

SCN9A-rs13017637 was a significant predictor of grade 2 or higher TIPN (odds ratio (OR) = 3.463; P = 0.0050) after correction for multiple comparisons, and precision was improved when only breast cancer patients were included (OR 5.053, P = 0.0029). Moreover, rs13017637 was a significant predictor of grade 2 or higher TIPN 1 year after treatment (OR 3.906, P = 0.037), indicating its contribution to TIPN duration.

Conclusion

SCN9A rs13017637 was associated with the severity and duration of TIPN. These findings are highly exploratory and require replication and validation prior to any consideration of clinical use.

Heterogeneous presentation of caspr2 antibody-associated peripheral neuropathy - A case series

Contactin-associated protein 2-like (caspr2) antibodies have been discovered recently. Since then a multitude of patients with caspr2 antibodies presenting with different neurological symptoms have been reported. Here, we describe three patients with caspr2 antibodies with different types of pain/no pain in combination with peripheral neuropathy. The first patient, a 33-year-old woman, presented with erythromelalgia-like pain and autonomic symptoms; the second patient, a 58-year-old man, with paresthesia and pain while walking together with signs of peripheral motor neuron hyperexcitability in combination with optic neuritis, and the third patient, a 74-year-old man, without any pain but with polyneuropathy and encephalopathy. These cases illustrate the spectrum of symptoms in anti-caspr2 diseases. The pain in such cases can be treated causally.

Chilblains

Idiopathic chilblain is a relatively common yet poorly recognized acrosyndrome. This literature review aims to better understand and draw attention to this disorder. Chilblain is a localized inflammation of the skin that occurs on exposure to cold but non-freezing wet weather. It usually resolves spontaneously. The etiology is uncertain, but vasospasm seems to play a role in this abnormal reaction to cold. Diagnosis is most often based on clinical presentation, but a skin biopsy can be useful in dubious cases. In histology, dermal edema and an inflammatory infiltrate are usually present. A distribution of the infiltrate particularly around the eccrine gland is typical. Systemic symptoms and underlying autoimmune disease should be screened. Avoiding cold and keeping extremities warm is the first recommendation for management, as well as smoking cessation. Calcium channel blockers (in particular nifedipine) seems to be the treatment that has been most evaluated in chilblains. However, their effectiveness is not confirmed by all studies. Topical betamethasone is often used but its effect has not been confirmed by randomized clinical trials. Other treatments, such as pentoxifylline, hydrochloroquine and topical nitroglycerin have shown positive effects only in a reduced number of patients. Acupuncture seems to bring a benefit.

[Erythromelalgia: skin redness and pain]

Erythromelalgia is a rare disease that is associated with hemato-oncological diseases or after taking certain drugs and toxins, but it can also occur as an independent clinical picture, for example, due to mutations in the sodium channel Na_V1.7. Clinically, there is a characteristic triad of attack-like burning pain and skin redness in the area of the distal extremities, which can be alleviated by excessive cooling. The attacks are triggered by heat, exertion, and stress. The diagnosis is primarily made clinically and can be confirmed by genetic testing if a sodium channel Na_V1.7 mutation is present. Important differential diagnoses are complex regional pain syndrome, the non-freezing cold injury, and small fiber neuropathies. Therapy is multidisciplinary and has to be planned individually and include physical therapy and psychotherapy as well as drug therapy as integral components.

Vascular acrosyndromes in young adult population. Definition of clinical symptoms and connections to joint hypermobility

OBJECTIVES

Clinical recognition of vascular acrosyndromes is often challenging. The term Raynaud's phenomenon (RP) is commonly overused to describe any form of cold-related disorder. This study aims to formally evaluate peripheral vascular symptoms affecting the population, aged ≤ 40 years, and identify any correlations to joint hypermobility (JH).

PATIENTS AND METHODS

Fifty patients (31 males, 19 females) with vasomotor symptoms enrolled in this five-year prospective observational study. Clinical examination by a rheumatologist and a vascular surgeon was performed along with cardiology, echocardiographic and Doppler evaluation. Patients underwent blood cell count, biochemistry, thyroid and selectively immunologic testing. Twenty-four (48%) of them performed nailfold capillaroscopy. The SPSS for Windows, v.17.0, Chicago, USA, was used for the statistical analyses.

RESULTS

Twenty-eight patients (56%) presented with erythromelalgia (EM), 6 (12%) with acrocyanosis (AC) and 9 (18%) as a combination of the above disorder. RP diagnosed in five (10%) while two patients (4%) presented as a mix of EM-RP. There was no correlation with abnormal laboratory tests. Increased incidence of JH was found in EM and AC patients. Among those who were tested with nailfold capillaroscopy, 75% had abnormalities ranged from mild to autoimmune-like diseases.

CONCLUSIONS

Erythromelalgia is the commonest functional vasculopathy in young population followed by acrocyanosis and a combination of these conditions. Joint hypermobility is markedly increased, indicating that dysautonomy may be considered the causative factor following a trigger event. Overall, RP was observed in 14% of patients. Clinical recognition of these disorders avoids unnecessary investigation. Key Points • Vascular acrosyndromes in young adults are commonly functional disorders resembling vascular algodystrophy induced by thermic stress. • Dysautonomy of joint hypermobility is the co-factor influencing the appearance of the vascular disorders. • Raynaud's phenomenon accounts to approximately 14% of vascular acrosyndromes presented in the young adult population.

Targeting Neuropathic Pain: Pathobiology, Current Treatment and Peptidomimetics as a New Therapeutic Opportunity

There is a huge need for pharmaceutical agents for the treatment of chronic Neuropathic Pain (NP), a complex condition where patients can suffer from either hyperalgesia or allodynia originating from central or peripheral nerve injuries. To date, the therapeutic guidelines include the use of tricyclic antidepressants, serotonin-noradrenaline reuptake inhibitors and anticonvulsants, beside the use of natural compounds and non-pharmacological options. Unfortunately, these drugs suffer from limited efficacy and serious dose-dependent adverse effects. In the last decades, the heptapeptide SP1-7, the major bioactive metabolite produced by Substance P (SP) cleavage, has been extensively investigated as a potential target for the development of novel peptidomimetic molecules to treat NP. Although the physiological effects of this SP fragment have been studied in detail, the mechanism behind its action is not fully clarified and the target for SP1-7 has not been identified yet. Nevertheless, specific binding sites for the heptapeptide have been found in brain and spinal cord of both mouse and rats. Several Structure-Affinity Relationship (SAR) studies on SP1-7 and some of its synthetic analogues have been carried out aiming to developing more metabolically stable and effective small molecule SP1-7-related amides that could be used as research tools for a better understanding of the SP1-7 system and, in a longer perspective, as potential therapeutic agents for future treatment of NP.

Homozygous NMNAT2 mutation in sisters with polyneuropathy and erythromelalgia

We identified a homozygous missense mutation in the gene encoding NAD synthesizing enzyme NMNAT2 in two siblings with childhood onset polyneuropathy with erythromelalgia. No additional homozygotes for this rare allele, which leads to amino acid substitution T94M, were present among the unaffected relatives tested or in the 60,000 exomes of the ExAC database. For axons to survive, axonal NMNAT2 activity has to be maintained above a threshold level but the T94M mutation confers a partial loss of function both in the ability of NMNAT2 to support axon survival and in its enzymatic properties. Electrophysiological tests and histological analysis of sural nerve biopsies in the patients were consistent with loss of distal sensory and motor axons. Thus, it is likely that NMNAT2 mutation causes this pain and axon loss phenotype making this the first disorder associated with mutation of a key regulator of Wallerian-like axon degeneration in humans. This supports indications from numerous animal studies that the Wallerian degeneration pathway is important in human disease and raises important questions about which other human phenotypes could be linked to this gene.

Erythromelalgia and Peripheral Nerve Block: A Case Report

A 79-year-old woman with primary erythromelalgia underwent a left reverse total shoulder arthroplasty with a left interscalene nerve block, a superficial cervical plexus block, and a general endotracheal anesthetic, with no residual neurological deficits. Herein, we discuss the classification and pathophysiology of erythromelalgia along with the anesthetic considerations of peripheral nerve blockade in patients with primary erythromelalgia.