OBJECTIVE: To develop a standardised, automated protocol for detecting protein gene product 9.5 (PGP9.5) positive intra-epidermal nerve fibres (IENFs) in skin biopsies, transitioning from the established manual technique to an automated platform. This automated method, although currently intended for research applications, may improve the accessibility of this diagnostic test for small fibre neuropathy in clinical settings.
METHODS: Skin biopsies (n = 274) from 100 participants (fibromyalgia syndrome n = 62; idiopathic small fibre neuropathy: n = 16; healthy volunteers: n = 22) were processed using an automated immunohistochemistry platform. IENF quantification was performed by blinded examiners, with reliability assessed via a two-way mixed-effects model to evaluate inter- and intra-observer variability.
RESULTS: The automated staining system reproduced intra-epidermal nerve fibre density (IENFD) counts consistent with free-floating sections (mean ± standard deviation: free-floating: 5.6 ± 3.4 fibres/mm; automated: 5.9 ± 3.2 fibres/mm). A median difference of 0.3 with a lower bound 95% Confidence Interval (CI) at -0.00005 established non-inferiority against a margin of -0.4 (p = .08). Specifically, the inter-class correlation coefficient (class denotes consistency in measured observations) was 99% (95% CI: 0.9-1), indicating excellent agreement between free-floating and automated methods. The inter- and intra-class coefficient between examiners were both 99% (95% CI: 0.9-0.1) for IENFD, demonstrating high reliability using sections stained using the automated method.
CONCLUSIONS: Automated immunohistochemistry provides high-throughput reliable and reproducible intra-epidermal nerve fibre quantification. This method, although currently proof-of-concept, for research use only, may be more widely deployed in histopathology laboratories to increase the adoption of IENFD assessment for the diagnosis of peripheral neuropathies.

Small-Fiber Neuropathy (SFN) is a disorder of the peripheral nervous system, characterised by neuropathic pain; approximately 11% of cases are linked to variants in Voltage-Gated Sodium Channels (VGSCs). This study aims to broaden the genetic knowledge on painful SFN by applying Whole-Exome Sequencing (WES) in Early-Onset (EO) cases. A total of 88 patients from Italy (n = 52) and the Netherlands (n = 36), with a disease onset at age ≤ 45 years old and a Pain Numerical Rating Score ≥ 4, were recruited. After variant filtering and classification, WES analysis identified 142 potentially causative variants in 93 genes; 8 are Pathogenic, 15 are Likely Pathogenic, and 119 are Variants of Uncertain Significance. Notably, an enrichment of variants in transient receptor potential genes was observed, suggesting their role in pain modulation alongside VGSCs. A pathway analysis performed by comparing EO cases with 40 Italian healthy controls found enriched mutated genes in the \"Nicotinic acetylcholine receptor signaling pathway\". Targeting this pathway with non-opioid drugs could offer novel therapeutic avenues for painful SFN. Additionally, with this study we demonstrated that employing a gene panel of reported mutated genes could serve as an initial screening tool for SFN in genetic studies, enhancing clinical diagnostics.

Background: The investigation of C-fiber-evoked ultralow-level responses (ULEPs) at somatic sites is difficult in clinical practice but may be useful in patients with small fiber neuropathy. Aim: The aim of the study was to investigate changes in LEPs and ULEPs in patients with fibromyalgia affected or not by abnormal intraepidermal innervation. Methods: We recorded LEPs and ULEPs of the hand, thigh and foot in 13 FM patients with a normal skin biopsy (NFM), 13 patients with a reduced intraepidermal nerve fiber density (IENFD) (AFM) and 13 age-matched controls. We used a YAP laser, changing the energy and spot size at the pain threshold for LEPs and at the heat threshold for ULEPs. Results: ULEPs occurred at a small number of sites in both the NFM and AFM groups compared to control subjects. The absence of ULEPs during foot stimulation was characteristic of AFM patients. The amplitude of LEPs and ULEPs was reduced in patients with AFM at the three stimulation sites, and a slight reduction was also observed in the NFM group. Conclusions: The present preliminary results confirmed the reliability of LEPs in detecting small fiber impairments. The complete absence of ULEPs in the upper and lower limbs, including the distal areas, could confirm the results of LEPs in patients with small fiber impairments. Further prospective studies in larger case series could confirm the present findings on the sensitivity of LEP amplitude and ULEP imaging in detecting small fiber impairments and the development of IENFD in FM patients.

OBJECTIVE: Small fiber neuropathy presents a significant diagnostic and therapeutic challenge. To solve this challenge, efforts have been made to identify autoantibodies associated with this condition. Previous literature has often considered tri-sulfated heparin disaccharide (TS-HDS) and fibroblast growth factor receptor 3 (FGFR3) as a singular seropositive group and/or focused primarily on symptomatic associations.
METHODS: One hundred seventy-two small fiber neuropathy patients with a Washington University Sensory Neuropathy panel were selected for TS-HDS seropositivity, FGFR-3 seropositivity, and seronegative controls. Data were collected to on the demographic, symptomatic, and laboratory profiles of each subgroup.
RESULTS: Percent female (P = 0.0043), frequency of neuropathic pain symptoms (P = 0.0074), and erythrocyte sedimentation rate (P = 0.0293), vitamin D (P < 0.0001), and vitamin B12 (P = 0.0033) differed between the groups. Skin biopsy was more frequently normal within both the FGFR-3 and the TS-HDS cohort (P = 0.0253).
CONCLUSIONS: TS-HDS and FGFR-3 display a distinct phenotype from both controls and one another. Immunoglobulin M (IgM) against FGFR-3 and IgM against TS-HDS may be individually valuable markers for the development of distinct clinical phenotypes.

OBJECTIVE: To report a case-control study of new-onset small fiber neuropathy (SFN) after COVID-19 with invasive cardiopulmonary exercise testing (iCPET). SFN is a critical objective finding in long COVID and amenable to treatment.
METHODS: A retrospective chart review was conducted on patients seen in the NeuroCOVID Clinic at Yale who developed new-onset SFN after a documented COVID-19 illness. We collected demographics, symptoms, skin biopsy, iCPET testing, treatments, and clinical response to treatment or no intervention.
RESULTS: Sixteen patients were diagnosed with SFN on skin biopsy (median age 47, 75% female, 75% White). 92% of patients reported postexertional malaise characteristic of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), and 7 patients underwent iCPET, which demonstrated neurovascular dysregulation and dysautonomia consistent with ME/CFS. Nine patients underwent treatment with IVIG, and 7 were not treated with IVIG. The IVIG group experienced significant clinical response in their neuropathic symptoms (9/9) compared with those who did not receive IVIG (3/7; p = 0.02).
CONCLUSIONS: Here, we present preliminary evidence that after COVID-19, SFN is responsive to treatment with IVIG and linked with neurovascular dysregulation and dysautonomia on iCPET. A larger clinical trial is indicated to further demonstrate the clinical utility of IVIG in treating postinfectious SFN.
METHODS: This study provides Class III evidence. It is a retrospective cohort study.

BACKGROUND: 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).
CONCLUSIONS: 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.

OBJECTIVE: To determine in children, adolescent and young adult (CAYA) patients presenting with Orthostatic Intolerance (OI) or Postural Orthostatic Tachycardia Syndrome (POTS) associated with the additional symptoms of neuropathic discomfort (pain, paresthesia and/or allodynia): 1) the incidence of small fiber neuropathy, and 2) assess if there was serologic evidence for an underlying inflammatory or autoimmune state.
METHODS: A cohort of 109 CAYA patients with the above symptoms underwent epidermal skin biopsy for nerve fiber density. Blood biomarkers for inflammation were tested (CRP, ESR, ANA, complement (C3), thyroid function testing with antibodies (thyroid peroxidase antibody and thyroglobulin antibody), and cytokine panel 13). Patients completed a Quality of Health questionnaire. Statistical analysis was performed using Wilcoxon rank sum tests.
RESULTS: In CAYA patients with OI or POTS and neuropathic symptoms, skin biopsy for small fiber neuropathy was abnormal in 53 %. The sample population was predominantly female and Caucasian with moderately decreased perceived quality of health. OI /POTS patients with small fiber neuropathy had a 3-fold probability of having a positive ANA or anti-thyroid antibody, suggesting an underlying autoimmune or inflammatory process.
CONCLUSIONS: Our data suggest a link between OI and POTS and small fiber neuropathy. Small fiber neuropathy was found by skin biopsy in over half of the patients tested. OI and Postural orthostatic tachycardia patients with small fiber neuropathy expressed multiple markers suggesting an underlying autoimmune or inflammatory process. Future research will be done to evaluate the symptomatic implication of SFN and whether immune or pharmacologic manipulation can alter patient symptoms.

OBJECTIVE: 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.
CONCLUSIONS: 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.
UNASSIGNED: 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.
BACKGROUND: Not applicable.

Small fiber neuropathy (SFN) is a well-defined chronic painful condition causing severe individual and societal burden. While mood disorders have been described, cognitive and behavioral profiles of SFN patients has not been investigated.
Thirty-four painful SFN patients underwent comprehensive cognitive, behavioral, psychological, quality of life (QoL), and personality assessment using validated questionnaires. As control samples, we enrolled 36 patients with painful peripheral neuropathy (PPN) of mixed etiology and 30 healthy controls (HC). Clinical measures of neuropathic pain, duration, frequency, and intensity of pain at the time of assessment were recorded. Between-group and correlation analyses were performed and corrected for multiple comparisons.
No differences in clinical measures were found between SFN and PPN, and all groups had similar cognitive profiles. SFN patients showed higher levels of anxiety and alexithymia (p < .005) compared to PPN and HC, considering also pain intensity. Maladaptive coping strategies characterized both patient groups, but only SFN revealed higher levels of acceptance of pain (p < .05). Pain intensity and neuropathic symptoms were associated with mood, low QoL and catastrophism (p < .001), particularly, the higher the perceived pain intensity, the higher the use of maladaptive coping strategies (p < .001). The personality assessment revealed significant feelings of worthlessness and somatization traits both in SFN and PPN (p < .002 vs HC).
our results suggest that SFN patients had a normal-like cognitive profile, while their behavioral profile is characterized by mood disorders, alexithymia, maladaptive coping strategies, and poor QoL, as other chronic pain conditions, possibly related to pain intensity. Personality assessment suggests that somatization and feelings of worthlessness, which may worsen the neuropsychological profile, deserve clinical attention when considering patients\' therapeutic approaches. At the same time, the high level of acceptance of pain is promising for therapeutic approaches based on psychological support.

OBJECTIVE: We aimed to investigate to what extent small fiber tests were abnormal in an unselected retrospective patient material with symptoms suggesting that small fiber neuropathy (SFN) could be present, and to evaluate possible gender differences.
METHODS: Nerve conduction studies (NCS), skin biopsy for determination of intraepidermal nerve fiber density (IENFD) and quantitative sensory testing (QST) were performed. Z-scores were calculated from reference materials to adjust for the effects of age and gender/height.
RESULTS: Two hundred and three patients, 148 females and 55 males had normal NCS and were considered to have possible SFN. 45.3 % had reduced IENFD, 43.2 % of the females and 50.9 % of the males. Mean IENFD was 7.3 ± 2.6 fibers/mm in females and 6.1 ± 2.3 in males (p<0.001), but the difference was not significant when adopting Z-scores. Comparison of gender differences between those with normal and abnormal IENFD were not significant when Z-scores were applied. QST was abnormal in 50 % of the patients (48.9 % in females and 52.9 % in males). In the low IENFD group 45 cases out of 90 (50 %) were recorded with abnormal QST. In those with normal IENFD 51 of 102 (50 %) showed abnormal QST.
CONCLUSIONS: Less than half of these patients had reduced IENFD, and 50 % had abnormal QST. There were no gender differences. A more strict selection of patients might have increased the sensitivity, but functional changes in unmyelinated nerve fibers are also known to occur with normal IENFD. Approval to collect data was given by the Norwegian data protection authority at University Hospital of North Norway (Project no. 02028).