Search

Erythromelalgia is a rare disorder characterized by episodic burning pain with redness and warmth of the extremities. Topical and systemic medications are the mainstay of management. We reviewed the published evidence for using procedural interventions to manage erythromelalgia, including their proposed mechanism of action and possible adverse effects, and included information in this review on epidural infusion, sympathetic ganglion block, sympathectomy, pulsed radiofrequency, spinal cord stimulation, dorsal root ganglion stimulation, brain stimulation, transcranial magnetic stimulation, and botulinum toxin injections. Both successful and unsuccessful outcomes have been reported. Although these procedural interventions extend the therapeutic options for erythromelalgia, the evidence for their use is limited. Case reports and small case series comprise most of the evidence. Based on our review, a multidisciplinary approach to management may be needed for patients with erythromelalgia., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: Red Ear Syndrome is a burning sensation and erythema of the ear, associated with a various number of disorders including migraine, trigeminal neuralgia, autoimmune disorders etc. Theories for RES pathophysiology have developed from current understandings of comorbid conditions. Characterizing the underlying mechanism of RES is crucial for defining effective treatments., Case Presentation: Three caucasian patients, ages 15, 47, and 67 years, with migraine, one with erythromelalgia are reported in this manuscript. RES pathophysiology is not fully understood due to its variable clinical presentation and numerous comorbid conditions, making it difficult to identify effective treatments., Conclusion: RES seems to be largely treatment-resistant, and most options involve treating the associated disorders and minimizing pain. Further investigation of future cases should lead to a more comprehensive understanding of the fundamental cause of RES and, hopefully, successful treatments., (© 2024. The Author(s).)

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., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: Small-fiber neuropathy is rare in children. It has been associated with several autoimmune disorders, but there are no reports of an autoinflammatory etiology., Methods: The data of four children/adolescents presenting with erythromelalgia and neuropathic pain from 2014 to 2019 were collected retrospectively from the electronic database of a pediatric medical center., Results: Results of clinical and/or electrophysiological evaluation excluded large nerve fiber involvement. Skin biopsy results confirmed small-fiber neuropathy. According to genetic analysis, two patients were heterozygous and one was homozygous for mutations in the familial Mediterranean fever (MEFV) gene. Behcet disease was diagnosed in the fourth patient. Treatment with anti-interleukin-1 agents, intravenous immunoglobulin, and glucocorticoids was beneficial., Discussion: The diagnosis of small-fiber neuropathy should be considered in children/adolescents presenting with erythromelalgia. A thorough investigation is required to reveal the underlying disorder. Clinicians should be alert to the peripheral neurological manifestations of autoinflammatory syndromes because effective treatments are available., (© 2020 Wiley Periodicals, Inc.)

The chronic pain syndrome inherited erythromelalgia (IEM) is attributed to mutations in the voltage-gated sodium channel (NaV) 1.7. Still, recent studies targeting NaV1.7 in clinical trials have provided conflicting results. Here, we differentiated induced pluripotent stem cells from IEM patients with the NaV1.7/I848T mutation into sensory nociceptors. Action potentials in these IEM nociceptors displayed a decreased firing threshold, an enhanced upstroke, and afterhyperpolarization, all of which may explain the increased pain experienced by patients. Subsequently, we investigated the voltage dependence of the tetrodotoxin-sensitive NaV activation in these human sensory neurons using a specific prepulse voltage protocol. The IEM mutation induced a hyperpolarizing shift of NaV activation, which leads to activation of NaV1.7 at more negative potentials. Our results indicate that NaV1.7 is not active during subthreshold depolarizations, but that its activity defines the action potential threshold and contributes significantly to the action potential upstroke. Thus, our model system with induced pluripotent stem cell-derived sensory neurons provides a new rationale for NaV1.7 function and promises to be valuable as a translational tool to profile and develop more efficacious clinical analgesics.

Pain is a complex process that involves both detection in the peripheral nervous system and perception in the CNS. Individual-to-individual differences in pain are well documented, but not well understood. Here we capitalized on inherited erythromelalgia (IEM), a well characterized human genetic model of chronic pain, and studied a unique family containing related IEM subjects with the same disease-causing Na V 1.7 mutation, which is known to make dorsal root ganglion (DRG) neurons hyperexcitable, but different pain profiles (affected son with severe pain, affected mother with moderate pain, and an unaffected father). We show, first, that, at least in some cases, relative sensitivity to pain can be modeled in subject-specific induced pluripotent stem cell (iPSC)-derived sensory neurons in vitro ; second, that, in some cases, mechanisms operating in peripheral sensory neurons contribute to interindividual differences in pain; and third, using whole exome sequencing (WES) and dynamic clamp, we show that it is possible to pinpoint a specific variant of another gene, KCNQ in this particular kindred, that modulates the excitability of iPSC-derived sensory neurons in this family. While different gene variants may modulate DRG neuron excitability and thereby contribute to interindividual differences in pain in other families, this study shows that subject-specific iPSCs can be used to model interindividual differences in pain. We further provide proof-of-principle that iPSCs, WES, and dynamic clamp can be used to investigate peripheral mechanisms and pinpoint specific gene variants that modulate pain signaling and contribute to interindividual differences in pain. SIGNIFICANCE STATEMENT Individual-to-individual differences in pain are well documented, but not well understood. In this study, we show, first, that, at least in some cases, relative sensitivity to pain can be modeled in subject-specific induced pluripotent stem cell-derived sensory neurons in vitro ; second, that, in some cases, mechanisms operating in peripheral sensory neurons contribute to interindividual differences in pain; and third, using whole exome sequencing and dynamic clamp, we show that it is possible to pinpoint a specific gene variant that modulates pain signaling and contributes to interindividual differences in pain., (Copyright © 2019 the authors 0270-6474/19/390382-11$15.00/0.)

Objective: Erythromelalgia is highly disabling and treatment is often very challenging. There have been solitary case reports that it might benefit from sympathectomy. This study sought to evaluate the short-term and long-term efficacy of chemical lumbar sympathectomy (CLS) for treatment of recalcitrant erythromelalgia and try to identify a CLS-responsive subset., Methods: Patients with recalcitrant erythromelalgia were recruited from a tertiary hospital over a 10-year period. L3 to L4 CLS was performed using 5% phenol. The pain intensity score (visual analog scale [VAS] 0-10) was assessed before CLS and at 1 day, 1 week, 3 months, 6 months, 1 year, and 2 years after CLS. A VAS decrease of 90%-100% is defined as complete response, 60%-89% as major partial response. Relapse was defined by a return of a VAS score of 5 or higher. SCN9A gene mutations were screened., Results: Thirteen patients were enrolled, with a median age of 15 years. The mean follow-up was 6.2 ± 3.8 years. SCN9A gene mutation was identified in five patients having family histories. The VAS was 8.2 ± 2.0 at baseline; it decreased to 4.9 ± 2.7 at 1 day and 1.9 ± 3.0 at 1 week after CLS. Nine patients (69.2%) achieved complete response at 1 week after CLS, including three patients with SCN9A gene mutation. Among the three complete response patients having the gene mutation, two reverted to major partial response and one relapsed at 2 years after CLS. Among the six complete response patients without mutation, five maintained complete response and one relapsed. Among the four patients who did not achieve complete response, one patient died at 3.5 months and one patient had an amputation performed at 4 months after CLS., Conclusions: CLS provides a valid option for the treatment of recalcitrant erythromelalgia. It takes about 1 week to achieve full efficacy. Relapse may occur, especially in patients with an SCN9A gene mutation., (Copyright © 2018 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.)

Mutations in the sodium-channel Na v 1.7, encoded by the gene SCN9A, are known to cause pain disorders. In particular, gain-of-function missense mutations in Na v 1.7 have been shown to be causal in primary erythromelalgia. We present a patient with erythromelalgia, pain attacks and hyperosmia with a mutation within the sodium-channel gene SCN9A. A 50-year-old woman presented with burning pain in both feet and abdominal pain attacks developed over the course of 10 years. Furthermore, this patient experienced a hypersensitivity for odours. Clinical investigation as well as serum/cerebrospinal fluid laboratory findings and electrophysiological testing were unremarkable. Olfactory testing showed high olfactory acuity for all screened modalities and good intranasal sensitivity. Furthermore, quantitative sensory testing within the trigeminal area revealed very low thresholds for thermal, tactile and pain detection. In addition, quantitative sensory testing at the lower legs showed hyperalgesia and, as the disease progresses, thermal sensory function loss. Skin biopsies of the proximal and distal lower limbs revealed reduced epidermal nerve fibre density indicating small fibre neuropathy. Genetic analysis of the SCN9A gene demonstrated a heterozygous mutation in Exon 20 - c.3734A>G (p.N1245S). Treatment with clinically available sodium-channel inhibitors did not result in significant pain relief. Local application of the sodium-channel blocker ambroxol however, reduced pain intensity. Continuous odour exposure stabilised mood and induced a short-term pain relief. This clinical note illustrates the course of middle-age onset erythromelalgia and points to clinical findings related to a likely pathogenic missense mutation affecting the sodium-channel Na v 1.7. SIGNIFICANCE: This case report illustrates the course of middle-age onset erythromelalgia with presumed gain-of-function in olfactory and pain sensation associated with a Nav1.7 channel mutation., (© 2018 European Pain Federation - EFIC®.)

A 36-year-old woman sustained a Grade 2 ankle sprain at work. Two days after the injury, the ankle and foot became red and she complained of "intense burning pain." First diagnosed with complex reflex sympathetic dystrophy, the employee was prescribed medications that provided some pain relief; a subsequent temporary nerve block provided additional relief. However, the symptoms returned and she was treated unsuccessfully with surgical sympathectomy. The employee was referred to a neurologist and diagnosed with primary erythromelalgia, a rare pain disorder that can be mistaken as complex reflex sympathetic dystrophy.

Objectives: Nociceptive thresholds and supra-threshold pain ratings as well as their reduction upon local injection with lidocaine were compared between healthy subjects and patients with erythromelalgia (EM)., Methods: Lidocaine (0.25, 0.50, 1.0 or 10 mg/mL) or placebo (saline) was injected intradermally in non-painful areas of the lower arm, in a randomized, double-blind manner, to test the effect on dynamic and static mechanical sensitivity, mechanical pain sensitivity, thermal thresholds and supra-threshold heat pain sensitivity., Results: Heat pain thresholds and pain ratings to supra-threshold heat stimulation did not differ between EM-patients (n = 27) and controls (n = 25), neither did the dose-response curves for lidocaine. Only the subgroup of EM-patients with mutations in sodium channel subunits Na V 1.7, 1.8 or 1.9 (n = 8) had increased lidocaine sensitivity for supra-threshold heat stimuli, contrasting lower sensitivity to strong mechanical stimuli. This pattern was particularly clear in the two patients carrying the Na V 1.7 I848T mutations in whom lidocaine's hyperalgesic effect on mechanical pain sensitivity contrasted more effective heat analgesia., Conclusion: Heat pain thresholds are not sensitized in EM patients, even in those with gain-of-function mutations in Na V 1.7. Differential lidocaine sensitivity was overt only for noxious stimuli in the supra-threshold range suggesting that sensitized supra-threshold encoding is important for the clinical pain phenotype in EM in addition to lower activation threshold. Intracutaneous lidocaine dose-dependently blocked nociceptive sensations, but we did not identify EM patients with particular high lidocaine sensitivity that could have provided valuable therapeutic guidance., Significance: Acute pain thresholds and supra-threshold heat pain in controls and patients with erythromelalgia do not differ and have the same lidocaine sensitivity. Acute heat pain thresholds even in EM patients with the Na V 1.7 I848T mutation are normal and only nociceptor sensitivity to intradermal lidocaine is changed. Only in EM patients with mutations in Na V 1.7, 1.8 or 1.9 supra-threshold heat and mechanical pain shows differential lidocaine sensitivity as compared to controls., (© 2017 European Pain Federation - EFIC®.)

Inherited erythromelalgia (IEM) is a well-described pain disorder caused by mutations of sodium channel Na v 1.7, a peripheral channel expressed within dorsal root ganglion and the sympathetic ganglion neurons. Clinically, IEM is characterised by paroxysmal attacks of severe pain, usually in the distal extremities, triggered by warmth or exercise. Pain is not adequately treated by existing pharmacological agents. Individuals with IEM classically cool their limbs for relief, in some cases resulting in tissue injury. We describe a patient from a family with IEM due to the L858F mutation of Na v 1.7 who presented with refractory hypothermia due to overcooling. This presentation of refractory hypothermia necessitating warming strategies, complicated by severe warmth-induced pain, posed a substantial therapeutic challenge. We report our experience in overcoming hypothermia lasting 3 weeks in a child with IEM, discuss possible pathophysiological mechanisms underlying this unusual complication and suggest potential therapeutic interventions., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Ltd (unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Purpose: Fabry disease is an X-linked genetic disorder caused by the mutations of α-galactosidase A (GLA, MIM 300644) gene presenting with various clinical symptoms including small-fiber peripheral neuropathy and limb burning pain. Here, we reported a Chinese pedigree with the initial diagnosis of primary erythromelalgia in an autosomal dominant (AD)-inherited pattern., Methods: Mutation analysis of SCN9A and GLA genes by direct sequencing and functional analysis of a novel mutation of GLA in cells were performed., Results: Our data did not show any pathological mutations in SCN9A gene; however, a novel missense mutation c.139T>C (p.W47R) of GLA was identified in a male proband as well as two female carriers in this family. Enzyme assay of α-galactosidase A activity showed deficient enzyme activity in male patients and female carriers, further confirming the diagnosis of Fabry disease. Finally, a functional analysis indicated that the replacement of the 47th amino acid tryptophan (W47) with arginine (W47R) or glycine (W47G) led to reduced activity of α-galactosidase A in 293T cells. Therefore, these findings demonstrated that the novel mutation p.W47R of GLA is the cause of Fabry disease., Conclusions: Because Fabry disease and primary erythromelalgia share similar symptoms, it is a good strategy for clinical physicians to perform genetic mutation screenings on both SCN9A and GLA genes in those patients with limb burning pain but without a clear inheritant pattern.

Gain-of-function mutations in the tetrodotoxin (TTX) sensitive voltage-gated sodium channel (Nav) Nav1.7 have been identified as a key mechanism underlying chronic pain in inherited erythromelalgia. Mutations in TTX resistant channels, such as Nav1.8 or Nav1.9, were recently connected with inherited chronic pain syndromes. Here, we investigated the effects of the p.M650K mutation in Nav1.8 in a 53 year old patient with erythromelalgia by microneurography and patch-clamp techniques. Recordings of the patient's peripheral nerve fibers showed increased activity dependent slowing (ADS) in CMi and less spontaneous firing compared to a control group of erythromelalgia patients without Nav mutations. To evaluate the impact of the p.M650K mutation on neuronal firing and channel gating, we performed current and voltage-clamp recordings on transfected sensory neurons (DRGs) and neuroblastoma cells. The p.M650K mutation shifted steady-state fast inactivation of Nav1.8 to more hyperpolarized potentials and did not significantly alter any other tested gating behaviors. The AP half-width was significantly broader and the stimulated action potential firing rate was reduced for M650K transfected DRGs compared to WT. We discuss the potential link between enhanced steady state fast inactivation, broader action potential width and the potential physiological consequences., Competing Interests: AMR, ZZ, HS, DM, PW, JK were employees of AstraZeneca (Sweden) at the time of the study. THC is a current employee of AstraZeneca (UK) and owns shares in AstraZeneca. This did not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

Introduction: The sodium channel Nav 1.9 is expressed in peripheral nociceptors and has recently been linked to human pain conditions, but the exact role of Nav 1.9 for human nociceptor excitability is still unclear., Methods: C-nociceptors from two patients with late onset of erythromelalgia-like pain, signs of small fiber neuropathy, and rare genetic variants of Nav 1.9 (N1169S, I1293V) were assessed by microneurography., Results: Compared with patients with comparable pain phenotypes (erythromelalgia-like pain without Nav-mutations and painful polyneuropathy), there was a tendency toward more activity-dependent slowing of conduction velocity in mechanoinsensitive C-nociceptors. Hyperexcitability to heating and electrical stimulation were seen in some nociceptors, and other unspecific signs of increased excitability, including spontaneous activity and mechanical sensitization, were also observed., Conclusions: Although the functional roles of these genetic variants are still unknown, the microneurography findings may be compatible with increased C-nociceptor excitability based on increased Nav 1.9 function.

Erythromelalgia is a rare condition characterized by burning pain, erythema and increased temperature of the hands or the feet. Its etiology is not completely understood but it is believed that the underlying cause is a peripheral vascular dysfunction that leads to simultaneous tissue hypoxia and hyperemia. We present a rare co-occurrence of erythromelalgia and multiple sclerosis in a patient with autonomic nervous system dysfunction and propose a causative interconnection., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Etiological and clinical heterogeneity of small fiber neuropathy (SFN) precludes a unifying approach and necessitates reliance on recognizable clinical syndromes. Symptoms of SFN arise from dysfunction in nociception, temperature, and autonomic modalities. This review focuses on SFN involving nociception and temperature, examining epidemiology, etiology, clinical presentation, diagnosis, pathophysiology, and management. Prevalence of SFN is 52.95 per 100,000 population, and diabetes and idiopathic are the most common etiologies. Dysesthesia, allodynia, pain, burning, and coldness sensations frequently present in a length-dependent pattern. Additional autonomic features in gastrointestinal, urinary, or cardiovascular systems are frequent but poorly objectified. SFN is diagnosed by intraepidermal nerve fiber density and quantitative sensory and autonomic tests in combination with normal nerve conduction. Pathophysiological understanding centers on sodium channel dysfunction, and genetic forms are beginning to be understood. Treatment is directed at the underlying etiology supported by symptomatic treatment using antidepressants and anticonvulsants. Little is known about long-term outcomes, and systematic cohort studies are needed., (© 2016 Wiley Periodicals, Inc.)

Inherited erythromelalgia, the first human pain syndrome linked to voltage-gated sodium channels, is widely regarded as a genetic model of human pain. Because inherited erythromelalgia was linked to gain-of-function changes of sodium channel Na(v)1.7 only a decade ago, the literature has mainly consisted of reports of genetic and/or clinical characterization of individual patients. This paper describes the pattern of pain, natural history, somatosensory profile, psychosocial status and olfactory testing of 13 subjects with primary inherited erythromelalgia with mutations of SCN9A, the gene encoding Na(v)1.7. Subjects were clinically profiled using questionnaires, quantitative sensory testing and olfaction testing during the in-clinic phase of the study. In addition, a detailed pain phenotype for each subject was obtained over a 3-month period at home using diaries, enabling subjects to self-report pain attacks, potential triggers, duration and severity of pain. All subjects reported pain and heat in the extremities (usually feet and/or hands), with pain attacks triggered by heat or exercise and relieved mainly by non-pharmacological manoeuvres such as cooling. A large proportion of pain attacks (355/1099; 32%) did not involve a specific trigger. There was considerable variability in the number, duration and severity of pain attacks between subjects, even those carrying the same mutation within a family, and within individuals over the 12-13 week observation period. Most subjects (11/13) had pain between attacks. For these subjects, mean pain severity between pain attacks was usually lower than that during an attack. Olfaction testing using the Sniffin'T test did not demonstrate hyperosmia. One subject had evidence of orthostatic hypotension. Overall, there was a statistically significant correlation between total Hospital Anxiety and Depression Scale scores (P= 0.005) and pain between attacks and for Hospital Anxiety and Depression Scale Depression scores and pain between attacks (P= 0.001). Hospital Anxiety and Depression Scale scores for five subjects were below the threshold for mild anxiety or depression and none of the 13 subjects were severely anxious and/or depressed. Quantitative sensory testing revealed significantly increased detection thresholds for cold and warm stimuli at affected, compared to unaffected sites. By contrast, significantly decreased cold and heat pain thresholds were found at unaffected sites. Sensory profiles varied considerably between affected and unaffected sites, suggesting the existence of small fibre neuropathy in symptomatic sites. This in-depth clinical characterization of a well-defined inherited erythromelalgia population indicates the importance of characterizing the pain phenotype in individuals before undertaking clinical trials, given the inherent variability of pain both between and within inherited erythromelalgia subjects, even those within a family who carry the same mutation., (© The Author (2016). Published by Oxford University Press on behalf of the Guarantors of Brain. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Aim: To investigate whether Aδ and C fibre pain threshold values, measured using intra-epidermal electrical stimulation (IES), in people with and without Type 2 diabetes are useful in evaluating diabetic polyneuropathy (DPN) severity., Methods: Aδ and C fibre pain threshold values were measured in Japanese people with (n = 120) and without (n = 76) Type 2 diabetes by IES. Nerve conduction studies and other tests were performed to evaluate diabetic complications., Results: Aδ and C fibre pain threshold values were high in people with diabetes compared with control subjects (Aδ fibre: 0.050 vs. 0.030 mA, P < 0.01; C fibre: 0.180 vs. 0.070 mA, P < 0.01). Participants with diabetes and neuropathy had significantly higher Aδ and C fibre pain threshold values than participants without neuropathy (Aδ fibres 0.063 vs. 0.039 mA, P < 0.01; C fibres 0.202 vs. 0.098 mA, P < 0.05). C fibre pain threshold values were significantly higher in participants with diabetes and diabetic microvascular complications than in participants without complications. Threshold values increased with complication progression. When DPN was diagnosed according to the Diabetic Neuropathy Study Group in Japan criteria, the cut-off for the C fibre pain threshold values was 0.125 mA (area under the curve 0.758, sensitivity 81.5%, specificity 61.5%). The IES test took less time (P < 0.01) and was less invasive (P < 0.01) than the nerve conduction studies., Conclusions: Intra-epidermal electrical stimulation is a non-invasive and easy measurement of small fibre pain threshold values. It may be clinically useful for C fibre measurement to diagnose early DPN as defined by the Diabetic Neuropathy Study Group in Japan criteria., (© 2015 The Authors. Diabetic Medicine © 2015 Diabetes UK.)

Serious investigators of fibromyalgia (FM) realize the profound implications of finding features of small fiber neuropathy (SFN) in this disorder. For the first time, an easily reproducible and generally agreed upon, peripheral tissue lesion has been reported from multiple investigative centers. Understanding how this discovery relates to other features of FM, and how one might utilize it to better comprehend, and care for, afflicted patients' painful complaints remains a challenge, however. In this article we review how the SFN seen in FM may be placed in context, and suggest how such a tissue abnormality might be used to better understand the pathophysiology of FM, and plan for its effective treatment. We also suggest how finding SFN in FM implies the need for continued focused research within the area of neuropathic disease in FM.

Interval measures at the impairment level addressing symptoms and at the activity/participation level addressing daily and social restrictions have not been developed for small fiber neuropathy (SFN). We developed an SFN-specific Rasch-built overall disability scale (SFN-RODS©), an activity/participation scale at the interval level. A preliminary SFN-RODS containing 146 activity/participation items was assessed twice (reliability studies) in 238 patients with SFN. The ordinal-based 13-item SFN-symptoms inventory questionnaire (SFN-SIQ©) and pain-visual-analogue-scale were also assessed (validity studies). The pre-SFN-RODS and SFN-SIQ data were subjected to the Rasch analyses. The pre-SFN-RODS did not meet Rasch model expectations. Based on requirements, such as misfit statistics, differential item functioning, and local dependency, items were systematically removed and model fit improved. Finally, a 32-item SFN-RODS© scale was constructed that fulfilled all Rasch requirements, demonstrating acceptable reliability and validity scores. The 13-item SFN-SIQ© was successfully transformed to an interval Rasch-built measure fulfilling model's requirements. In conclusion, the 32-item SFN-RODS© is a disease-specific interval measure suitable for detecting activity limitations and participation restrictions in patients with SFN. The 13-item SFN-SIQ© was transformed through Rasch to an interval measure. The use of these scales is recommended in future clinical interventional trials involving patients with SFN., (© 2015 Peripheral Nerve Society.)

Introduction: Small-fiber pathology can develop in the acute phase of critical illness and may explain chronic sensory impairment and pain in critical care survivors., Methods: Eleven adult ischemic stroke patients in a neurocritical care unit were enrolled in an observational cohort study. Intraepidermal nerve fiber density (IENFD) in the distal leg was assessed on admission to the intensive care unit and 10-14 days later, together with electrophysiological testing., Results: Of the 11 patients recruited, 9 (82%) had sepsis or multiple-organ failure. Median IENFD on admission (5.05 fibers/mm) decreased significantly to 2.18 fibers/mm (P < 0.001), and abnormal IENFD was found in 6 patients (54.5%). Electrodiagnostic signs of large-fiber neuropathy and/or myopathy were found in 6 patients (54.5%), and autonomic dysfunction was found in 2 patients (18.2%)., Conclusion: Serial IENFD measurements confirmed the development of small-fiber sensory involvement in the acute phase of critical illness., (© 2014 Wiley Periodicals, Inc.)

Introduction: We examined optimization of a temperature threshold testing (TTT) protocol for patients with suspected small-fiber neuropathy (SFN) to lessen the burden for both patients and technicians, without sacrificing accuracy., Methods: Data from 81 patients with SFN (skin biopsy and TTT abnormal) and 81 without SFN (skin biopsy and TTT normal) were used. Warm, cold, and heat pain sensation thresholds were determined bilaterally on the thenar eminence and foot dorsum by methods of limits and levels. Diagnostic accuracy was determined for various sensory modality combinations through comparative corresponding area under the receiver-operator characteristic curves., Results: Assessment of warm and cold thresholds in all extremities by the method of levels showed the best discriminatory ability (area under the curve 0.95, sensitivity 84.2%, specificity 93.8%)., Conclusions: These assessments are suggested for TTT examination in possible SFN patients. By applying this combination, the time needed for TTT can be reduced, maintaining diagnostic accuracy., (© 2014 Wiley Periodicals, Inc.)

Objective: Routine electrophysiological testing is often normal in the evaluation of painful diabetic neuropathy, as it is unable to detect dysfunction of thinly myelinated (Aδ) and unmyelinated (C) small fibers. Although cutaneous silent periods (CSP) and quantitative sudomotor axon reflex testing (QSART) respectively evaluate these fiber types in the extremities, these two tests have yet to be assessed together., Methods: 26 patients with a clinical diagnosis of small fiber neuropathy (SFN) and 26 age-matched controls were assessed. Nine patients had Type I diabetes, nine had Type II diabetes, and eight had impaired glucose tolerance. The CSP onset latency and duration were recorded in each extremity. QSART was performed on the right side., Results: 58% (15/26) of patients had abnormal sweat volumes obtained from QSART, while 50% (13/26) of patients had abnormal CSP responses. Combining these two tests increased the sensitivity of testing to 77% (20/26). Abnormalities were seen equally across all patient groups., Conclusions: Combining CSP with QSART significantly increases the sensitivity of testing when assessing patients with SFN related to diabetes, or prediabetes., Significance: For clinically suspected SFN, it is preferable to test more than one small fiber type, as each possess different structural and functional properties and may be heterogeneously affected between patients., (Copyright © 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Introduction: Contact heat evoked potentials (CHEPs) may be an objective, non-invasive diagnostic tool in small-fiber neuropathy (SFN). This study establishes normal CHEP values and examines their applicability in SFN patients., Methods: Standardized CHEPs were administered at the wrist and ankle. The N2 and P2 latencies and N2 -P2 peak-peak amplitude were recorded by electroencephalography. We examined healthy subjects (n = 97), stratified by age and gender, and SFN patients with abnormal intraepidermal nerve fiber density (n = 42). CHEP reproducibility and interobserver values were also investigated., Results: CHEP normative values were determined. There was a 9-16% increase in latency per centimeter of height with increasing age. Amplitudes were higher in women than men, and decreased (17-71%) with aging. Test-retest reproducibility and interobserver values were >0.61 and >0.96, respectively. CHEPs were abnormal in 73.8% of the patients., Conclusion: In this study we have established normal values, reliability, and clinical applicability of CHEPs in SFN., (© 2014 Wiley Periodicals, Inc.)

Introduction: Vascular denervation occurs in some neuropathies, but measurement of small perivascular axons has been difficult., Methods: We evaluated 31 consecutive patients who had both muscle and skin biopsies. We quantitated myovascular innervation by staining unmyelinated axons with peripherin and non-myelinating Schwann cells with neural cell adhesion molecule and comparing their areas., Results: Perivascular unmyelinated axon-Schwann (UAS) ratios correlated with axon density in skin (r = 0.679; P < 0.0001). Low UAS ratios (≤0.25) had a sensitivity of 90% and specificity of 91% for a clinical diagnosis of small-fiber neuropathy (P < 0.0001). Autonomic features were more common in patients with low perivascular UAS ratios (P = 0.002). A patient subgroup with myovascular, but not skin, denervation commonly had muscle discomfort and autonomic features., Conclusions: UAS ratio measurements, comparing axons and associated non-myelinating Schwann cells, can quantitate perivascular innervation. Small-fiber neuropathies are often associated with myovascular denervation. Some patients with muscle discomfort have selective myovascular denervation., (© 2014 Wiley Periodicals, Inc.)

Human and mouse genetic studies have led to significant advances in our understanding of the role of voltage-gated sodium channels in pain pathways. In this chapter, we focus on Nav1.7, Nav1.8, Nav1.9 and Nav1.3 and describe the insights gained from the detailed analyses of global and conditional transgenic Nav knockout mice in terms of pain behaviour. The spectrum of human disorders caused by mutations in these channels is also outlined, concluding with a summary of recent progress in the development of selective Nav1.7 inhibitors for the treatment of pain.

Guillain-Barré syndrome (GBS) is a well-described condition involving the peripheral nervous system. The most well-known form of this disease is acute inflammatory demyelinating polyradiculoneuropathy. Among the different variants of GBS described in the literature, the sensory variant is scantily recognized. There has been a recent attempt to classify the sensory variants of the GBS and bring more objectivity to this diagnostic paradigm. We report a rare sensory variant of GBS presenting with isolated small nerve fiber involvement peripherally in the limbs and associated facial nerve palsy in a patient who had clinical and serological evidence of a preceding Mycoplasma pneumoniae infection. The symptoms resolved gradually with intravenous immunoglobulin therapy. This case adds to the growing literature of the rare form of acute small fiber neuropathy and GBS variants.

Objective: To characterize the burden of idiopathic painful peripheral neuropathy with small fiber involvement (idiopathic SFN) by pain severity in the US., Methods: One hundred previously diagnosed idiopathic SFN subjects were enrolled during routine office visits. Subjects completed a one-time questionnaire, and investigators reported clinical characteristics and healthcare resource use, based on 6 month retrospective chart review. Annualized direct and indirect costs were estimated. Results were stratified across pain severity groups., Results: Mean age was 63.5 years; 53.0% were female; 76.0% had moderate or severe pain. Most common comorbidities were sleep disturbance/insomnia (37.0%), anxiety (34.0%), and depressive symptoms (33.0%). Overall mean health status (0.59; -0.11-1.00 scale), physical and mental health (31.7 and 45.6, respectively, 0-100 scale), sleep index (45.1; 0-100 scale), and pain interference with function (5.0; 0-10 scale) differed by pain severity, with worse outcomes among those with greater pain (all p < 0.002). 84.0% were prescribed ≥1 SFN medication. 16.0% were employed; mean overall work impairment was 36.9%. Annualized average adjusted direct and indirect costs per subject ($8055 and $13,733, respectively) differed by pain severity., Conclusions: Idiopathic SFN subjects with pain experience moderate or severe pain, which negatively impacts health status, function, and productivity, and leads to substantial direct and indirect costs.

Objective: To investigate the presence of small nerve fiber dysfunction in subjects with X-linked adrenoleukodystrophy., Methods: Cross-sectional study in which 11 Norwegian subjects (3 males, 8 females) with X-linked adrenoleukodystrophy, phenotypes ranging from asymptomatic to wheelchair-bound with adrenomyeloneuropathy, were investigated with neurophysiologic studies including EMG, nerve conduction velocities, quantitative sensory testing, tests of autonomic function, and skin biopsy for intraepidermal nerve fiber density measurements., Results: We found small nerve fiber dysfunction in 10 of 11 subjects, increasing with age and more pronounced in males. Low intraepidermal nerve fiber densities were found in 5 of 11 subjects, indicating a loss of thin unmyelinated nerve fibers peripherally. Five of 11 subjects showed small nerve fiber dysfunction despite normal nerve fiber densities, suggesting possible involvement of the spinothalamic tracts. Two subjects showed moderate abnormalities in autonomic function tests., Conclusions: Evidence of small nerve fiber dysfunction was widespread in this cohort of subjects with X-linked adrenoleukodystrophy, with findings indicating loss of peripheral small nerve fibers and possibly also fibers of the spinothalamic tracts. The results support the theory of primary axonal degeneration in adrenomyeloneuropathy. Evidence of nervous system involvement was found in all heterozygotes, with severity increasing with age. Clinicians caring for these patients should be alert to signs of small nerve fiber involvement.

Introduction: Fibromyalgia (FM) is a chronic syndrome characterized by widespread pain often accompanied by other symptoms suggestive of neuropathic pain. We evaluated patients for small fiber neuropathy (SFN) who were referred for fibromyalgia (FM)., Methods: We studied 20 consecutive subjects with primary FM. Patients underwent neurological examination, nerve conduction studies, and skin biopsies from distal leg and thigh., Results: Electrodiagnostic studies were normal in all patients. SFN was diagnosed in 6 patients by reduced epidermal nerve fiber density. These patients also showed abnormalities of both adrenergic and cholinergic fibers., Conclusions: A subset of FM subjects have SFN, which may contribute to their sensory and autonomic symptoms. Skin biopsy should be considered in the diagnostic work-up of FM., (Copyright © 2013 Wiley Periodicals, Inc.)

Objective: Painful small fibre neuropathy (SFN) represents a significant public health problem, with no cause apparent in one-half of cases (termed idiopathic, I-SFN). Gain-of-function mutations of sodium channel NaV1.7 have recently been identified in nearly 30% of patients with biopsy-confirmed I-SFN. More recently, gain-of-function mutations of NaV1.8 have been found in patients with I-SFN. These NaV1.8 mutations accelerate recovery from inactivation, enhance the response to slow depolarisations, and enhance activation at the channel level, thereby producing hyperexcitability of small dorsal root ganglion (DRG) neurons, which include nociceptors, at the cellular level. Identification and functional profiling of additional NaV1.8 variants are necessary to determine the spectrum of changes in channel properties that underlie DRG neuron hyperexcitability in these patients., Methods: Two patients with painful SFN were evaluated by skin biopsy, quantitative sensory testing, nerve conduction studies, screening of genomic DNA for mutations in SCN9A and SCN10A and electrophysiological functional analysis., Results: A novel sodium channel NaV1.8 mutation G1662S was identified in both patients. Voltage-clamp analysis revealed that the NaV1.8/G1662S substitution impairs fast-inactivation, depolarising the midpoint (V1/2) by approximately 7 mV. Expression of G1662S mutant channels within DRG neurons rendered these cells hyperexcitable., Conclusions: We report for the first time a mutation of NaV1.8 which impairs inactivation, in patients with painful I-SFN. Together with our earlier results, our observations indicate that an array of NaV1.8 mutations, which affect channel function in multiple ways, can contribute to the pathophysiology of painful peripheral neuropathy.

It is well known that transthyretin-related familial amyloidotic polyneuropathy (TTR-FAP) and diabetic peripheral neuropathy are characterized by early selective involvement of small nerve fibers. However, early diagnosis of these diseases is not easy because prominent early diagnostic markers for small fiber neuropathies have not established. Thus, we adopted several methods to evaluate autonomic function accurately for detecting the onset of small-fiber neuropathy, such as laser-Doppler flowmetry, sweating tests using capsule type sweating ratemeter, morphological check of sweat gland, electrogastrography, density check of small-fiber and gastrointestinal interstitial cells of Cajal, R-R interval study, (123)I-MIBG myocardial scintigraphy, and head-up tilt test to check the overshoot phenomenon. These tests may indicate very early stage of small-fiber neuropathies in asymptomatic mutated TTR carriers or impaired glucose tolerance patients. Moreover, assessment of the pain thresholds by preferential stimulation of C and Aδ fibers are particularly useful tools for diagnosing the onset of small-fiber neuropathies in addition to the autonomic testing.

Objective: Sudomotor dysfunction due to small fiber neuropathy can be observed very early in pre-diabetes. The aim of this study was to assess the predictive power of EZSCAN, a non invasive, quick and simple measurement of sudomotor function to identify glucose impairment., Research Design and Methods: The study was performed in 76 German subjects at risk of diabetes. Glucose metabolism was assessed by using, oral glucose tolerance test (OGTT) at baseline and after 2 year follow-up. Sudomotor function was evaluated by measuring hand and foot electrochemical sweat conductances to calculate a risk score., Results: At baseline, 38 patients had normal glucose tolerance (NGT), 34 had pre-diabetes (impaired fasting glucose, IFG and/or impaired glucose tolerance, IGT) and 4 had newly diagnosed type 2 diabetes. The AUC values for FPG, 2h-OGTT glucose, 1h-OGTT glucose, HbA1C and EZSCAN score to predict pre-diabetes were 0.50, 0.65, 0.64, 0.72 and 0.76, respectively. Subjects having a moderate or high EZSCAN score (>50) at baseline had a substantially increased risk for having IFG and/or IGT at follow-up visit presented by an odds ratio of 12.0 [1.4-100.5], the OR for having 1h-OGTT ≥ 8.6mmol/L at follow-up was 9.8 [1.0-92.8] and for having HbA1C ≥ 5.7% was 15.7 [1.9-131.5] compared to subjects with low EZSCAN risk., Conclusions: This preliminary study, which must be confirmed in a larger population, shows that EZSCAN risk score is associated with diabetes progression which have implications for prevention and disease management., (Copyright © 2013. Published by Elsevier Ltd.)

Introduction: We examined the role of skin biopsy in the evaluation and management of patients with suspected small fiber neuropathy (SFN)., Methods: A retrospective chart review was performed among all patients who underwent skin biopsy for evaluation of SFN at our institution between March 2008 and March 2011. Change in management was defined as a new diagnosis or change in treatment in response to both positive and negative skin biopsies., Results: Among 69 patients who underwent skin biopsy, 25 had pathological evidence of an SFN, and 9 had evidence of borderline SFN. Change in management or diagnosis occurred in 14 of 25 patients with definite SFN, 6 of 9 patients with borderline SFN, and 16 of 35 biopsy negative patients., Conclusions: Skin biopsy changed management or diagnosis in 52% of patients evaluated for a possible SFN and appears to play a valuable role in the workup of these patients., (Copyright © 2013 Wiley Periodicals, Inc.)

Introduction: We evaluated incorporation of the quantitative sudomotor axon reflex test (QSART) into the diagnostic criteria for small fiber neuropathy (SFN) as an addition to quantitative sensory testing (QST) and intraepidermal nerve fiber density (IENFD) testing., Methods: One hundred one patients with clinically suspected SFN underwent QSART, QST, and skin biopsy. The diagnostic yield of existing SFN criteria in these patients was compared with criteria incorporating QSART. The new combined diagnostic criteria were evaluated., Results: SFN was diagnosed in 38 of the 101 patients (38%) using current criteria. Addition of QSART existing SFN criteria resulted in an increased diagnostic yield to 67 patients (66%). Applying new SFN criteria requiring abnormality in at least 2 assessments among QSART, QST, and IENFD resulted in a diagnosis of SFN in 57 patients (56%)., Conclusion: Assessment of both somatic and peripheral autonomic small nerve fibers enhances diagnostic criteria for SFN., (Copyright © 2013 Wiley Periodicals, Inc.)

The assessment of functional deficits in small fibre neuropathies (SFN) requires using ancillary tests other than conventional neurophysiological techniques. One of the tests with most widespread use is thermal threshold determination, as part of quantitative sensory testing. Thermal thresholds typically reflect one point in the whole subjective experience elicited by a thermal stimulus. We reasoned that more information could be obtained by analyzing the subjective description of the ongoing sensation elicited by slow temperature changes (dynamic thermal testing, DTT). Twenty SFN patients and 20 healthy subjects were requested to describe, by using an electronic visual analog scale system, the sensation perceived when the temperature of a thermode was made to slowly change according to a predetermined pattern. The thermode was attached to the left ventral forearm or the distal third of the left leg and the stimulus was either a monophasic heat or cold stimuli that reached 120% of pain threshold and reversed to get back to baseline at a rate of 0.5 °C/s. Abnormalities seen in patients in comparison to healthy subjects were: (1) delayed perception of temperature changes, both at onset and at reversal, (2) longer duration of pain perception at peak temperature, and (3) absence of an overshoot sensation after reversal, ie, a transient perception of the opposite sensation before the temperature reached again baseline. The use of DTT increases the yield of thermal testing for clinical and physiological studies. It adds information that can be discriminant between healthy subjects and SFN patients and shows physiological details about the process of activation and inactivation of temperature receptors that may be abnormal in SFN., (Copyright © 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Background: Degeneration of intraepidermal nerve fibers (IENF) is a hallmark of small fiber neuropathy of different etiology, whose clinical picture is dominated by neuropathic pain. It is unknown if critical illness can affect IENF., Methods: We enrolled 14 adult neurocritical care patients with prolonged intensive care unit (ICU) stay and artificial ventilation (≥ 3 days), and no previous history or risk factors for neuromuscular disease. All patients underwent neurological examination including evaluation of consciousness, sensory functions, muscle strength, nerve conduction study and needle electromyography, autonomic dysfunction using the finger wrinkling test, and skin biopsy for quantification of IENF and sweat gland innervation density during ICU stay and at follow-up visit. Development of infection, sepsis and multiple organ failure was recorded throughout the ICU stay., Results: Of the 14 patients recruited, 13 (93%) had infections, sepsis or multiple organ failure. All had severe and non-length dependent loss of IENF. Sweat gland innervation was reduced in all except one patient. Of the 7 patients available for follow-up visit, three complained of diffuse sensory loss and burning pain, and another three showed clinical dysautonomia., Conclusions: Small fiber pathology can develop in the acute phase of critical illness and may explain chronic sensory impairment and pain in neurocritical care survivors. Its impact on long term disability warrants further studies involving also non-neurologic critical care patients.

We identified and clinically investigated two patients with primary erythromelalgia mutations (PEM), which are the first reported to map to the fourth domain of Nav1.7 (DIV). The identified mutations (A1746G and W1538R) were cloned and transfected to cell cultures followed by electrophysiological analysis in whole-cell configuration. The investigated patients presented with PEM, while age of onset was very different (3 vs. 61 years of age). Electrophysiological characterization revealed that the early onset A1746G mutation leads to a marked hyperpolarizing shift in voltage dependence of steady-state activation, larger window currents, faster activation kinetics (time-to-peak current) and recovery from steady-state inactivation compared to wild-type Nav1.7, indicating a pronounced gain-of-function. Furthermore, we found a hyperpolarizing shift in voltage dependence of slow inactivation, which is another feature commonly found in Nav1.7 mutations associated with PEM. In silico neuron simulation revealed reduced firing thresholds and increased repetitive firing, both indicating hyperexcitability. The late-onset W1538R mutation also revealed gain-of-function properties, although to a lesser extent. Our findings demonstrate that mutations encoding for DIV of Nav1.7 can not only be linked to congenital insensitivity to pain or paroxysmal extreme pain disorder but can also be causative of PEM, if voltage dependency of channel activation is affected. This supports the view that the degree of biophysical property changes caused by a mutation may have an impact on age of clinical manifestation of PEM. In summary, these findings extent the genotype-phenotype correlation profile for SCN9A and highlight a new region of Nav1.7 that is implicated in PEM.

Background: Erythromelalgia is an uncommon neurovascular disorder characterized by redness, increased skin temperature, and pain that usually occurs in the extremities. Treatment remains challenging because of its varying response to medical therapy. The objective of this study was to assess the response of erythromelalgia to compounded topical amitriptyline-ketamine., Methods: We retrospectively evaluated 36 patients with erythromelalgia who were treated with compounded topical amitriptyline-ketamine from January 1, 2004, through January 31, 2011., Results: Thirty-two patients (89%) were female. Mean (standard deviation) age was 44.7 (15.8) years (range, 5-74 years). Patients applied the medication 1 to 6 times per day (median, 5 times). One patient (3%) had complete relief from symptoms, 14 (39%) had substantial relief, 12 (33%) had some relief, 7 (19%) had no relief, and 2 (6%) had local worsening of symptoms. No patients had systemic adverse effects., Conclusions: A majority of patients with erythromelalgia (75%) reported improvement in pain with topical application of a compounded amitriptyline-ketamine formulation. The medication was well tolerated.

Gain-of-function missense mutations of SCN9A gene, which encodes voltage-gated sodium channel Nav1.7, alter channel's biophysical properties causing painful disorders which are refractory to pharmacotherapy in the vast majority of patients. Here we report a novel SCN9A mutation (ca.T3947C) in exon 20 in a 9 year old patient, not present in 200 ethnically-matched control alleles; the mutation substitutes the invariant valine 1316 residue within DIII/S5 by alanine (V1316A). Voltage-clamp studies show that Nav1.7 V1316A mutation hyperpolarizes activation (-9 mV), and enhances response to ramp stimuli (3-fold), changes that are predicted to cause hyperexcitability of DRG neurons. V1316A also hyperpolarizes steady-state slow-inactivation (-9.9 mV), which is predicted to attenuate the effect of this mutation on DRG neuron firing. These changes are consistent with previously characterized Erytheromelalgia associated mutations of Nav1.7., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: Erythromelalgia is a rare disorder characterized by the clinical syndrome of burning pain, warmth and redness of the limbs. Neurological abnormalities (both large- and small-fibre neuropathy) are common. There have been few published reports on the sensory status of patients with erythromelalgia., Aim: To investigate the results of quantitative sensation testing in erythromelalgia using computer-assisted sensory evaluation, including vibratory detection threshold, cool detection threshold and heat-pain threshold (HPT)., Methods: Patients who underwent dermatological or neurological evaluation of suspected erythromelalgia at our institution and received a final diagnosis of erythromelalgia were identified from a master diagnosis index covering the period January 1994 to June 2008. A retrospective chart review was performed. Main outcome measures were sensory abnormalities (e.g. pain, burning sensation, tingling) in response to heat, cooling and vibration during computer-assisted sensory testing., Results: In total, 41 patients with erythromelalgia were enrolled in the study and underwent computer-assisted sensory evaluation. Of these, 34 patients (82.9%) had abnormal results. The commonest abnormality was isolated HPT: 11 patients (26.8%) had heat hypoalgesia and 18 (43.9%) had heat hyperalgesia, whereas only 2 (4.9%) of the healthy control patients had hyperalgesia on testing., Conclusions: Multiple sensory modalities were found to be abnormal in patients with erythromelalgia, with the commonest clinical abnormality being isolated heat-pain abnormality. These findings lend support to the notion that neuropathy underlies the clinical diagnosis of erythromelalgia. Future studies will explore the nature of the relationship between these sensory abnormalities and the clinical features of erythromelalgia., (© Mayo Foundation for Medical Education and Research. CED © 2012 British Association of Dermatologists.)

We identified a patient with severe inherited erythromelalgia secondary to an L858F mutation in the voltage-gated sodium channel Na(v)1.7. The patient reported severe ongoing foot pain, which was exquisitely sensitive to limb cooling. We confirmed this heat hypersensitivity using quantitative sensory testing. Additionally, we employed a novel perfusion imaging technique in a simple block design to assess her baseline erythromelalgia pain vs cooling relief. Robust activations of key pain, pain-affect, and reward-related centres were observed. This combined approach allowed us to confirm the presence of a temperature-sensitive channelopathy of peripheral neurons and to investigate the neural correlates of tonic neuropathic pain and relief in a single subject., (Copyright © 2012 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Perturbations to body temperature affect almost all cellular processes and, within certain limits, results in minimal effects on overall physiology. Genetic mutations to ion channels, or channelopathies, can shift the fine homeostatic balance resulting in a decreased threshold to temperature induced disturbances. This review summarizes the functional consequences of currently identified voltage-gated sodium (NaV) channelopathies that lead to disorders with a temperature sensitive phenotype. A comprehensive knowledge of the relationships between genotype and environment is not only important for understanding the etiology of disease, but also for developing safe and effective treatment paradigms.