Background and purposeSmall fiber neuropathy (SFN) is a common disorder leading to neuropathic pain and autonomic symptoms. The objective of this study was to investigate associated conditions in a large cohort of SFN patients and compare the prevalence to healthy individuals.MethodsA total of 921 patients with pure SFN were screened according to a standardized comprehensive diagnostic algorithm and compared with literature findings.ResultsNo associated condition could be found in 53% of the patients. Autoimmune diseases, sodium channel gene mutations, diabetes mellitus including glucose intolerance, and vitamin B12 deficiencies were more prevalent than reported literature findings, followed by alcohol abuse, chemotherapy, monoclonal gammopathy of undetermined significance, and haemochromatosis. In patients who were already known with a possible underlying condition at screening, additional underlying conditions were still found in another 26.7% of patients.ConclusionsBased on these results, it is recommended that patients with pure SFN are screened at least for autoimmune diseases, sodium channel gene mutations, diabetes mellitus including glucose intolerance, and vitamin B12 deficiency, even when they already have a potential underlying condition at referral.

BackgroundNeuropathic pain is common in peripheral neuropathy. Recent genetic studies have linked pathogenic voltage-gated sodium channel (VGSC) variants to human pain disorders. Our aims are to determine the frequency of SCN9A, SCN10A and SCN11A variants in patients with pure small fibre neuropathy (SFN), analyse their clinical features and provide a rationale for genetic screening.MethodsBetween September 2009 and January 2017, 1139 patients diagnosed with pure SFN at our reference centre were screened for SCN9A, SCN10A and SCN11A variants. Pathogenicity of variants was classified according to established guidelines of the Association for Clinical Genetic Science and frequencies were determined. Patients with SFN were grouped according to the VGSC variants detected, and clinical features were compared.ResultsAmong 1139 patients with SFN, 132 (11.6%) patients harboured 73 different (potentially) pathogenic VGSC variants, of which 50 were novel and 22 were found in ≥ 1 patient. The frequency of (potentially) pathogenic variants was 5.1% (n=58/1139) for SCN9A, 3.7% (n=42/1139) for SCN10A and 2.9% (n=33/1139) for SCN11A. Only erythromelalgia-like symptoms and warmth-induced pain were significantly more common in patients harbouring VGSC variants.Conclusion(Potentially) pathogenic VGSC variants are present in 11.6% of patients with pure SFN. Therefore, genetic screening of SCN9A, SCN10A and SCN11A should be considered in patients with pure SFN, independently of clinical features or underlying conditions.

Objective:This is the first double-blind, randomized, controlled trial evaluating the efficacy and safety of intravenous immunoglobulin (IVIg) versus placebo in patients with idiopathic small fiber neuropathy (I-SFN).Methods:Between July 2016 and November 2018, 60 Dutch patients with skin-biopsy proven idiopathic SFN randomly received a starting dose of IVIg (2 g/kg body weight) or matching placebo (0.9% saline). Subsequently, 3 additional infusions of IVIg (1 g/kg) or placebo were administered at 3-weekly intervals. The primary outcome was a 1-point change in Pain Intensity Numerical Rating Scale (PI-NRS) at 12 weeks compared to baseline.Results:Thirty patients received IVIg, and 30 received placebo. In both groups, 29 patients completed the trial. In 40% of patients receiving IVIg, the mean average pain was decreased with at least 1 point, compared to 30% of the patients receiving placebo (p-value 0.588, OR 1.56, 95%CI 0.53-4.53). No significant differences were found on any of the other pre-specified outcomes including general wellbeing, autonomic symptoms, and overall functioning and disability.Conclusions:This RCT showed that IVIg treatment had no significant effect on pain in patients with painful idiopathic SFN.