Patient satisfaction and patient accessibility in a small fiber neuropathy diagnostic service in the Netherlands: A single-center, prospective, survey-based cohort study.

INTRODUCTION: Small fiber neuropathy (SFN) is a common cause of neuropathic pain in peripheral neuropathies. Good accessibility of diagnostics and treatment is necessary for an accurate diagnosis and treatment of SFN. Evidence is lacking on the quality performance of the diagnostic SFN service in the Netherlands. Our aim was to determine the patient satisfaction and -accessibility of the diagnostic SFN service, and to identify areas for improvement. METHODS: In a single-center, prospective, survey-based cohort study, 100 visiting patients were asked to fill in the SFN patient satisfaction questionnaire (SFN-PSQ), with 10 domains and 51 items. Cut-off point for improvement was defined as ≥ 25% dissatisfaction on an item. A chi-square test and linear regression analyses was used for significant differences and associations of patient satisfaction. RESULTS: From November 2020 to May 2021, 98 patients with SFN-related complaints filled in the online SFN-PSQ within 20 minutes. In 84% of the patients SFN was confirmed, average age was 55.1 (52.5-57.8) years and 67% was female. High satisfaction was seen in the domains 'Waiting List Period', Chest X-ray', 'Consultation with the Doctor or Nurse Practitioner (NP)', 'Separate Consultation with the Doctor or NP about Psychological Symptoms', and 'General' of the SFN service. Overall average patient satisfaction score was 8.7 (IQR 8-10) on a 1-to-10 rating scale. Main area for improvement was shortening the 8-week period for receiving the results of the diagnostic testing (p < 0.05). General health status was statistically significant associated with patient satisfaction (p < 0.05). CONCLUSION: A good reflection of the high patient satisfaction and -accessibility of the SFN-service is shown, with important points for improvement. These results could help hospitals widely to optimize the logistic and diagnostic pathway of SFN analysis, benchmarking patient satisfaction results among the hospitals, and to improve the quality of care of comparable SFN services.

Development, validation and feasibility of a Patient Satisfaction Questionnaire for evaluating the quality performance of a diagnostic small fibre neuropathy service: A qualitative study.

INTRODUCTION AND AIM: Small fibre neuropathy (SFN) is a peripheral neuropathy, leading to neuropathic pain and autonomic dysfunction. An evidence-based standardized patient diagnostic SFN service has been implemented in the Netherlands for improving patient-centred SFN care. However, the quality of care of this diagnostic SFN service has never been assessed from a patient perspective. The aim of this study was to develop and validate an SFN-Patient Satisfaction Questionnaire (SFN-PSQ) to measure the quality performance of a standardized diagnostic SFN service. METHODS: A descriptive qualitative study to create the SFN-PSQ was performed using the (COREQ (Consolidated Criteria for Reporting Qualitative Research) checklist. For item generation and content development, domains and/or items from validated PSQs were selected. The content development and content validity were performed using a Delphi method with SFN expert caregivers with different backgrounds. By using the three-step-test method in individual cognitive interviews, the content validity by patients was finalized. RESULTS: In one online Delphi panel round, the content of the first concept of the SFN-PSQ was validated, which resulted in the second concept of the SFN-PSQ. From July 2019 till March 2020, nine patients consented to participate in the individual cognitive interviews. The most significant changes of the new questionnaire were adding domains and items concerning the waiting list, the diagnostic services and consultation by the hospital psychiatrist. Also, a differentiation was made for both an inpatient and outpatient diagnostic SFN service. Furthermore, the clarity and intelligibility of the domains/items were improved, resulting in an increased comprehension of the SFN-PSQ. Ultimately, the new developed SFN-PSQ consisted of 10 domains and 51 items, suitable for measuring patient satisfaction of the neurological analysis in patients with SFN. CONCLUSION: Through item generation, expert opinions and interviews with patients, the SFN-PSQ was developed and validated, and feasibility was confirmed. The structure of the questionnaire, based on the logistic and diagnostic SFN pathway, could be used as a model in other hospitals to improve the quality, continuity and access of SFN care and other chronic diseases taking into account potential cross-cultural differences. PATIENT OR PUBLIC CONTRIBUTION: Caregivers were involved in the item generation and content development of the questionnaire. Patients were directly involved in testing the content validity and feasibility of the SFN-PSQ. CLINICAL TRIAL REGISTRATION: Not applicable.

EURO-NMD registry: federated FAIR infrastructure, innovative technologies and concepts of a patient-centred registry for rare neuromuscular disorders.

BACKGROUND: The EURO-NMD Registry collects data from all neuromuscular patients seen at EURO-NMD's expert centres. In-kind contributions from three patient organisations have ensured that the registry is patient-centred, meaningful, and impactful. The consenting process covers other uses, such as research, cohort finding and trial readiness. RESULTS: The registry has three-layered datasets, with European Commission-mandated data elements (EU-CDEs), a set of cross-neuromuscular data elements (NMD-CDEs) and a dataset of disease-specific data elements that function modularly (DS-DEs). The registry captures clinical, neuromuscular imaging, neuromuscular histopathology, biological and genetic data and patient-reported outcomes in a computer-interpretable format using selected ontologies and classifications. The EURO-NMD registry is connected to the EURO-NMD Registry Hub through an interoperability layer. The Hub provides an entry point to other neuromuscular registries that follow the FAIR data stewardship principles and enable GDPR-compliant information exchange. Four national or disease-specific patient registries are interoperable with the EURO-NMD Registry, allowing for federated analysis across these different resources. CONCLUSIONS: Collectively, the Registry Hub brings together data that are currently siloed and fragmented to improve healthcare and advance research for neuromuscular diseases.

Peripheral Pain Captured Centrally: Altered Brain Morphology on MRI in Small Fiber Neuropathy Patients With and Without an SCN9A Gene Variant.

The current study aims to characterize brain morphology of pain as reported by small fiber neuropathy (SFN) patients with or without a gain-of-function variant involving the SCN9A gene and compare these with findings in healthy controls without pain. The Neuropathic Pain Scale was used in patients with idiopathic SFN (N = 20) and SCN9A-associated SFN (N = 12) to capture pain phenotype. T1-weighted, structural magnetic resonance imaging (MRI) data were collected in patients and healthy controls (N = 21) to 1) compare cortical thickness and subcortical volumes and 2) quantify the association between severity, quality, and duration of pain with morphological properties. SCN9A-associated SFN patients showed significant (P < .017, Bonferroni corrected) higher cortical thickness in sensorimotor regions, compared to idiopathic SFN patients, while lower cortical thickness was found in more functionally diverse regions (eg, posterior cingulate cortex). SFN patient groups combined demonstrated a significant (Spearman's ρ = .44-.55, P = .005-.049) correlation among itch sensations (Neuropathic Pain Scale-7) and thickness of the left precentral gyrus, and midcingulate cortices. Significant associations were found between thalamic volumes and duration of pain (left: ρ = -.37, P = .043; right: ρ = -.40, P = .025). No associations were found between morphological properties and other pain qualities. In conclusion, in SCN9A-associated SFN, profound morphological alterations anchored within the pain matrix are present. The association between itch sensations of pain and sensorimotor and midcingulate structures provides a novel basis for further examining neurobiological underpinnings of itch in SFN. PERSPECTIVE: Cortical thickness and subcortical volume alterations in SFN patients were found in pain hubs, more profound in SCN9A-associated neuropathy, and correlated with itch and durations of pain. These findings contribute to our understanding of the pathophysiological pathways underlying chronic neuropathic pain and symptoms of itch in SFN.

Cost of illness of patients with small fiber neuropathy in the Netherlands.

ABSTRACT: Neuropathic pain is associated with substantial healthcare costs. However, cost-of-illness studies of small fiber neuropathy (SFN) are scarce. Our aim was to estimate the healthcare, patient and family, and productivity costs of patients with SFN in the Netherlands from a healthcare and societal perspective. In addition, the association of costs with age, pain impact on daily life, anxiety, depression, and quality of life (Qol) were examined. Cost questionnaires were completed by 156 patients with confirmed SFN. The average annual total health care and societal cost (€, 2020) was calculated at patient, SFN adult population, and societal level. The average annual healthcare, patient and family, and productivity costs per patient with a Pain Impact Numerical Rating Scale of 0 to 3 (mild), 4 to 6 (moderate), and 7 to 10 (severe) were calculated by using the cost questionnaire data. Quality of life was determined by the EuroQol 5D utility scores. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale. Associations of all costs were analyzed using linear regression analyses. At the patient level, the average annual SFN healthcare and societal cost of SFN was €3614 (95% confidence interval [CI] €3171-€4072) and €17,871 (95% CI €14,395-€21,480). At the SFN population level, the average healthcare costs were €29.8 (CI €26.4-€34.2) million, and on a societal level, these were €147.7 (CI 120.5-176.3) million. Severe pain was associated with significant lower Qol and higher depression scores, higher healthcare, patient and family, and productivity costs ( P < 0.001).

Ion Channel Genes in Painful Neuropathies.

Neuropathic pain (NP) is a typical symptom of peripheral nerve disorders, including painful neuropathy. The biological mechanisms that control ion channels are important for many cell activities and are also therapeutic targets. Disruption of the cellular mechanisms that govern ion channel activity can contribute to pain pathophysiology. The voltage-gated sodium channel (VGSC) is the most researched ion channel in terms of NP; however, VGSC impairment is detected in only <20% of painful neuropathy patients. Here, we discuss the potential role of the other peripheral ion channels involved in sensory signaling (transient receptor potential cation channels), neuronal excitation regulation (potassium channels), involuntary action potential generation (hyperpolarization-activated cyclic nucleotide-gated channels), thermal pain (anoctamins), pH modulation (acid sensing ion channels), and neurotransmitter release (calcium channels) related to pain and their prospective role as therapeutic targets for painful neuropathy.

Acceptability, usability and feasibility of experienced sampling method in chronic secondary pain syndromes.

Background: In chronic pain syndromes, symptoms can fluctuate and change over time. Standard questionnaires cannot register these fluctuations. Nonetheless, the experience sampling method (ESM) is developed to collect momentary measurements of everyday complaints, tracing fluctuations in symptoms and disabling factors over time. Although valuable information can be collected in this way, assessment may also be a burden. This study aimed to investigate the acceptability, usability, and feasibility of ESM in chronic secondary pain syndromes, in a single-center study in the Netherlands. Methods: A prospective observational study with repeated measurements was conducted in patients with chronic secondary neuropathic and musculoskeletal pain syndromes, including small fiber neuropathy, spinal cord injury, and rheumatoid disorder. Results: Thirty-four participants were included and filled in the ESM, of whom 19 were diagnosed with small fiber neuropathy, 11 with spinal cord injury, and 4 with a rheumatoid disorder. The mean age was 54.7 ± 13.9 years (range: 23-77) of whom 52.9% were female. In total, 19 participants filled in the general and user-friendliness evaluation about the acceptability and usability of the ESM. The general evaluation showed no influence of ESM on participants' social contacts (mean 1.47, SD 1.12), activities (mean 1.74, SD 1.44), and mood (mean 1.89, SD 1.59). The answers options of ESM were a good representation of the experiences of participants (mean 4.58, SD 1.77). Regarding feasibility, the overall response rate for answering the beep signals of ESM was 44.5% in total. The missing rate per person varied from 13% to 97% with a median of 54.1%. Conclusion: The general evaluation and the user-friendliness revealed sufficient outcomes in favor of the ESM application. ESM seems a promising measurement tool to use in secondary chronic pain syndromes.

Genetic Profiling of Sodium Channels in Diabetic Painful and Painless and Idiopathic Painful and Painless Neuropathies.

Neuropathic pain is a frequent feature of diabetic peripheral neuropathy (DPN) and small fiber neuropathy (SFN). Resolving the genetic architecture of these painful neuropathies will lead to better disease management strategies, counselling and intervention. Our aims were to profile ten sodium channel genes (SCG) expressed in a nociceptive pathway in painful and painless DPN and painful and painless SFN patients, and to provide a perspective for clinicians who assess patients with painful peripheral neuropathy. Between June 2014 and September 2016, 1125 patients with painful-DPN (n = 237), painless-DPN (n = 309), painful-SFN (n = 547) and painless-SFN (n = 32), recruited in four different centers, were analyzed for SCN3A, SCN7A-SCN11A and SCN1B-SCN4B variants by single molecule Molecular inversion probes-Next Generation Sequence. Patients were grouped based on phenotype and the presence of SCG variants. Screening of SCN3A, SCN7A-SCN11A, and SCN1B-SCN4B revealed 125 different (potential) pathogenic variants in 194 patients (17.2%, n = 194/1125). A potential pathogenic variant was present in 18.1% (n = 142/784) of painful neuropathy patients vs. 15.2% (n = 52/341) of painless neuropathy patients (17.3% (n = 41/237) for painful-DPN patients, 14.9% (n = 46/309) for painless-DPN patients, 18.5% (n = 101/547) for painful-SFN patients, and 18.8% (n = 6/32) for painless-SFN patients). Of the variants detected, 70% were in SCN7A, SCN9A, SCN10A and SCN11A. The frequency of SCN9A and SCN11A variants was the highest in painful-SFN patients, SCN7A variants in painful-DPN patients, and SCN10A variants in painless-DPN patients. Our findings suggest that rare SCG genetic variants may contribute to the development of painful neuropathy. Genetic profiling and SCG variant identification should aid in a better understanding of the genetic variability in patients with painful and painless neuropathy, and may lead to better risk stratification and the development of more targeted and personalized pain treatments.

IgM anti-MAG± peripheral neuropathy (IMAGiNe) study protocol: An international, observational, prospective registry of patients with IgM M-protein peripheral neuropathies.

BACKGROUND: International consensus on IgM ± anti-MAG ± PNP (IgM PNP) is lacking. Despite increasing interest in clinical trials, validated disease-specific measures are needed to adequately capture limitations and changes over time. The IMAGiNe (IgM ± anti-myelin associated glycoprotein [MAG] peripheral neuropathy) study surges as an international collaboration to create a standardized registry of patients with IgM ± anti-MAG PNP. The consortium, which currently consists of 11 institutions from 7 countries, presents here the IMAGiNe study design and protocol. AIMS: Functional outcome measures will be constructed at the level of impairment, as well as activity and participation. We aim to describe the natural history of the cohort, the role of anti-MAG antibodies, the presence of clinical subtypes, and potential biomarkers. METHODS: The IMAGiNe study is a prospective, observational cohort study with a 3-year follow-up. At each assessment, researchers collect clinical data and subjects complete a list of preselected outcome measures. Among these, the "Pre-Rasch-built Overall Disability Scale (Pre-RODS)" questionnaire will be submitted to Rasch analysis to assess classic and modern clinimetric requirements. RESULTS: The final measures will include the IgM-PNP-specific RODS and Ataxia Rating Scale (IgM-PNP-ARS). Descriptions of the disease course, clinical heterogeneity, treatment regimes, variations in laboratory values, and antibody titers will help reach consensus on diagnosis and follow-up strategies. CONCLUSION: The constructed interval scales will be cross-culturally valid and suitable for use in future clinical trials and daily practice. The ultimate goals are to improve functional individualized assessment, reach international consensus, and lay the foundations for successful designs in future studies.

Outcomes after robotic thymectomy in nonthymomatous versus thymomatous patients with acetylcholine-receptor-antibody-associated myasthenia gravis.

The aim of this study was to investigate the surgical and long-term neurological outcomes of patients with acetylcholine-receptor-antibody-associated myasthenia gravis (AChR-MG) who underwent robotic thymectomy (RATS). We retrospectively analyzed the clinical-pathological data of all patients with AChR-MG who underwent RATS using the DaVinci® Robotic System at the MUMC+ between April 2004 and December 2018. Follow-up data were collected from 60 referring Dutch hospitals. In total, 230 myasthenic patients including 76 patients with a thymoma (33.0%) were enrolled in this study. Mean follow-up time, procedure time and hospitalization were, respectively 65.7 ± 43.1 months, 111±52.5 min and 3.3 ± 2.2 days. Thymomatous patients had significantly more frequently and more severe complications than nonthymomatous patients (18.4% vs. 3.9%, p<0.001). Follow up data was available in 71.7% of the included patients. The Myasthenia Gravis Foundation of America postintervention score showed any kind of improvement of MG-symptoms after RATS in 82.4% of the patients. Complete stable remission (CSR) or pharmacological remission (PR) of MG was observed in 8.4% and 39.4% of the patients, respectively. Mean time till CSR/PR remission after thymectomy was 26.2 ± 29.2 months. No statistical difference was found in remission or improvement in MGFA scale between thymomatous and nonthymomatous patients. RATS is safe and feasible in patients with MG. The majority of the patients (82.4%) improved after thymectomy. CSR and PR were observed in 8.4% and 39.4% of the patients, respectively, with a mean of 26.2 months after thymectomy. Thymomatous patients had more frequently and more severe complications compared to nonthymomatous patients.

Integrative miRNA-mRNA profiling of human epidermis: unique signature of SCN9A painful neuropathy.

Personalized management of neuropathic pain is an unmet clinical need due to heterogeneity of the underlying aetiologies, incompletely understood pathophysiological mechanisms and limited efficacy of existing treatments. Recent studies on microRNA in pain preclinical models have begun to yield insights into pain-related mechanisms, identifying nociception-related species differences and pinpointing potential drug candidates. With the aim of bridging the translational gap towards the clinic, we generated a human pain-related integrative miRNA and mRNA molecular profile of the epidermis, the tissue hosting small nerve fibres, in a deeply phenotyped cohort of patients with sodium channel-related painful neuropathy not responding to currently available therapies. We identified four miRNAs strongly discriminating patients from healthy individuals, confirming their effect on differentially expressed gene targets driving peripheral sensory transduction, transmission, modulation and post-transcriptional modifications, with strong effects on gene targets including NEDD4. We identified a complex epidermal miRNA-mRNA network based on tissue-specific experimental data suggesting a cross-talk between epidermal cells and axons in neuropathy pain. Using immunofluorescence assay and confocal microscopy, we observed that Nav1.7 signal intensity in keratinocytes strongly inversely correlated with NEDD4 expression that was downregulated by miR-30 family, suggesting post-transcriptional fine tuning of pain-related protein expression. Our targeted molecular profiling advances the understanding of specific neuropathic pain fine signatures and may accelerate process towards personalized medicine in patients with neuropathic pain.

Telemedicine in Neuromuscular Diseases During Covid-19 Pandemic: ERN-NMD European Survey.

BACKGROUND: Telemedicine (TM) contributes to bridge the gap between healthcare facilities and patients' homes with neuromuscular disease (NMD) because of mobility issues. However, its deployment is limited due to difficulties evaluating subtle neurological signs such as mild weakness or sensory deficits. The COVID-19 pandemic has disrupted healthcare delivery worldwide, necessitating rapid measures implementation by health care providers (HCPs) to protect patients from acquiring SARS-CoV-2 while maintaining the best care and treatment. OBJECTIVES: Given the challenges faced by remote healthcare assistance of NMD patients, we aim to evaluate the use of TM in NMD during the COVID-19 pandemic. METHODS: Based on the Model for Assessment-of-Telemedicine-Applications (MAST), we conducted a survey amongst clinicians of the ERN EURO NMD (European-Reference-Network-for-Rare-Neuromuscular-Diseases). RESULTS: Based on 42 responses over 76 expected ones, our results show that the COVID-19 pandemic significantly increased the number of HCPs using TM (from 60% to 100%). The TM types most used during the COVID-19 period are teleconsultation and consultation by phone, particularly in the context of symptoms worsening in NMD patients with COVID-19 infection. Most European HCPs were satisfied when using TM but as a complementary option to physical consultations. Many responses addressed the issue of technical aspects needing improvement, particularly for elderly patients who need caregivers' assistance for accessing the TM platform. CONCLUSIONS: TM has been essential during COVID-19, but its use still presents some limitations for NMD patients with cognitive deficits or for first-time diagnosis. Thus, TM should be used as complement to, rather than substitute, for face-to-face consultations.

Peripheral Ion Channel Genes Screening in Painful Small Fiber Neuropathy.

Neuropathic pain is a characteristic feature of small fiber neuropathy (SFN), which in 18% of the cases is caused by genetic variants in voltage-gated sodium ion channels. In this study, we assessed the role of fifteen other ion channels in neuropathic pain. Patients with SFN (n = 414) were analyzed for ANO1, ANO3, HCN1, KCNA2, KCNA4, KCNK18, KCNN1, KCNQ3, KCNQ5, KCNS1, TRPA1, TRPM8, TRPV1, TRPV3 and TRPV4 variants by single-molecule molecular inversion probes-next-generation sequencing. These patients did not have genetic variants in SCN3A, SCN7A-SCN11A and SCN1B-SCN4B. In twenty patients (20/414, 4.8%), a potentially pathogenic heterozygous variant was identified in an ion-channel gene (ICG). Variants were present in seven genes, for two patients (0.5%) in ANO3, one (0.2%) in KCNK18, two (0.5%) in KCNQ3, seven (1.7%) in TRPA1, three (0.7%) in TRPM8, three (0.7%) in TRPV1 and two (0.5%) in TRPV3. Variants in the TRP genes were the most frequent (n = 15, 3.6%), partly in patients with high mean maximal pain scores VAS = 9.65 ± 0.7 (n = 4). Patients with ICG variants reported more severe pain compared to patients without such variants (VAS = 9.36 ± 0.72 vs. VAS = 7.47 ± 2.37). This cohort study identified ICG variants in neuropathic pain in SFN, complementing previous findings of ICG variants in diabetic neuropathy. These data show that ICG variants are central in neuropathic pain of different etiologies and provides promising gene candidates for future research.

Living with small fiber neuropathy: insights from qualitative focus group interviews.

OBJECTIVE: Small fiber neuropathy (SFN) is characterized by chronic neuropathic pain and autonomic dysfunction. Currently, symptomatic pharmacological treatment is often insufficient and frequently causes side effects. SFN patients have a reduced quality of life. However, little is known regarding whether psycho-social variables influence the development and maintenance of SFN-related disability and complaints. Additional knowledge may have consequences for the treatment of SFN. For example, factors such as thinking, feeling, and behavior are known to play roles in other chronic pain conditions. The aim of this study was to obtain further in-depth information about the experience of living with SFN and related chronic pain. METHODS: Fifteen participants with idiopathic SFN participated in a prospective, semi-structured, qualitative, focus group interview study. The focus groups were audio-recorded, transcribed, and analyzed cyclically after each interview. RESULTS: The following main themes were identified: "pain appraisal", "coping", "social, work, and health environment", and "change in identity". Catastrophic thoughts and negative emotions were observed. Living with SFN resulted in daily limitations and reduced quality of life. CONCLUSIONS: Given the results, it can be concluded that an optimal treatment should include biological, psychological, and social components.

Anxiety and depression in small fiber neuropathy.

Psychiatric comorbidity is common in patients with chronic pain. In peripheral neuropathic pain, particularly anxiety and mood disorders are frequently present and associated with a high level of catastrophizing. Small fiber neuropathy (SFN) is a peripheral neuropathy dominated by pain. This study aimed to investigate the prevalence of and factors associated with anxiety and depressive symptoms in SFN. All consecutive patients diagnosed with SFN at Maastricht University Medical Center+, between September 2016 and October 2021, were included (n = 1310). Data on demographics, medical history, diagnostic tests, and questionnaires about pain, SFN-specific symptoms, and mental health were collected once. The Hospital Anxiety and Depression Scale (HADS) was used to measure anxiety and depression and the Pain Catastrophizing Scale (PCS) to measure the degree of catastrophizing. One-third of the patients had an abnormal HADS score (≥11) on the subscales anxiety and/or depression (26.5% anxiety and 23.0% depression) indicating clinical relevance. Regression analysis showed that higher pain intensity, catastrophizing, and more SFN-related complaints were significantly associated with an abnormal HADS-score. In conclusion, the prevalence of reported anxiety or depressive symptoms in SFN is 36.3%. A multidisciplinary approach, not only focusing on pain relief, is therefore essential for the treatment of SFN.

Pain triangle phenomenon in possible association with SCN9A: A case report.

BACKGROUND: Voltage-gated sodium channels are essential for the generation and conduction of electrical impulses in excitable cells. Sodium channel Nav 1.7, encoded by the SCN9A-gene, has been of special interest in the last decades because missense gain-of-function mutations have been linked to a spectrum of neuropathic pain conditions, including inherited erythermalgia (IEM), paroxysmal extreme pain disorder (PEPD), and small fiber neuropathy (SFN). METHODS: In this case report, we present a 61-year-old woman who was referred to our tertiary referral center in a standard day care setting with suspicion of SFN. We performed additional investigations: skin biopsy to determine the intra-epidermal nerve fiber density (IENFD), quantitative sensory testing (QST), and blood examination (including DNA analysis) for possible underlying conditions. RESULTS: The patient showed a clinical picture that fulfilled the criteria of IEM, PEPD, and SFN. DNA analysis revealed the heterozygous variant c.554G > A in the SCN9A-gene (OMIM 603415). This variant has already been described in all three human pain conditions separately, but never in one patient having symptoms of all three conditions. Because its pathogenicity has never been functionally confirmed, the variant is classified as a variance of unknown significance (VUS)/risk factor. This suggests that another genetic and/or environmental substrate plays a role in the development of neuropathic conditions like described. CONCLUSION: We have described this as the SCN9A-pain triangle phenomenon. Treatment should focus on pain management, genetic counseling, and improving/maintaining quality of life by treating symptoms and, if indicated, starting a rehabilitation program.

Small fiber neuropathies: expanding their etiologies.

PURPOSE OF REVIEW: Several conditions have been associated with the development of small fiber neuropathy (SFN). The list of metabolic, immune-mediated, infectious, toxic, drugs-related, and hereditary conditions is still growing and various hypotheses are made about the underlying pathophysiological mechanisms. Understanding these processes is important to provide new targets for treatment. In addition, the specific SFN phenotype can provide direction for the underlying etiology. This review discusses the latest developments concerning the expanding etiologies in SFN. RECENT FINDINGS: In the past 18 months, special attention has been paid to immunological etiologies, partly due to the coronavirus disease 2019 pandemic, but also new auto-antibodies in SFN have been demonstrated. Identifying patients with immune-mediated SFN can be challenging, since contrary to the classical distal sensory phenotype, a nonlength-dependent pattern is more common.Besides the etiologies of classical SFN, small fiber pathology is increasingly described in diseases without the typical neuropathic pain features of SFN, sometimes called syndromic SFN. However, the clinical relevance is not yet fully understood. SUMMARY: The expansion of the etiologies of SFN continues and brings more insight in possible targets for treatment. The clinical presentation may vary as a result of the underlying condition.

Peripheral Ion Channel Gene Screening in Painful- and Painless-Diabetic Neuropathy.

Neuropathic pain is common in diabetic peripheral neuropathy (DN), probably caused by pathogenic ion channel gene variants. Therefore, we performed molecular inversion probes-next generation sequencing of 5 transient receptor potential cation channels, 8 potassium channels and 2 calcium-activated chloride channel genes in 222 painful- and 304 painless-DN patients. Twelve painful-DN (5.4%) patients showed potentially pathogenic variants (five nonsense/frameshift, seven missense, one out-of-frame deletion) in ANO3 (n = 3), HCN1 (n = 1), KCNK18 (n = 2), TRPA1 (n = 3), TRPM8 (n = 3) and TRPV4 (n = 1) and fourteen painless-DN patients (4.6%-three nonsense/frameshift, nine missense, one out-of-frame deletion) in ANO1 (n = 1), KCNK18 (n = 3), KCNQ3 (n = 1), TRPA1 (n = 2), TRPM8 (n = 1), TRPV1 (n = 3) and TRPV4 (n = 3). Missense variants were present in both conditions, presumably with loss- or gain-of-functions. KCNK18 nonsense/frameshift variants were found in painless/painful-DN, making a causal role in pain less likely. Surprisingly, premature stop-codons with likely nonsense-mediated RNA-decay were more frequent in painful-DN. Although limited in number, painful-DN patients with ion channel gene variants reported higher maximal pain during the night and day. Moreover, painful-DN patients with TRP variants had abnormal thermal thresholds and more severe pain during the night and day. Our results suggest a role of ion channel gene variants in neuropathic pain, but functional validation is required.