113 with non-length dependent SFN.11 Second, patients with sodium channel mutations typically present with intermittent rather than continuous symptoms, similar to paroxysmal extreme pain disorder.9 Based on the heterogeneous clinical manifestations, diagnosing SFN remains a major challenge. In addition to genetic testing, several diagnostic tests have been developed to assess small nerve fibers, by determining nerve fiber density, sensory function, or autonomic function.12 A gold standard is currently lacking, but diagnostic criteria including intraepidermal nerve fiber density (IENFD) and thermal threshold testing (TTT) are widely recognized as useful modalities.13 Because both IENFD and TTT are measured distally, there is a risk of underdiagnosing SFN in patients with non-lengthdependent SFN.14 Corneal confocal microscopy (CCM), which measures corneal nerve fiber density (CNFD), has been suggested as a supplementary tool to specifically assess non-length-dependent nerve fiber loss.15 In addition, autonomic function tests show added value in diagnosing SFN.16 Sarcoidosis is an immune-mediated granulomatous disorder of unknown cause, mainly affecting the lungs and lymph nodes.17 SFN is a common complication in patients with sarcoidosis estimated to occur in 40-86%.18,19 The exact prevalence of length-dependent and non-length-dependent pain in sarcoidosis-associated SFN (SSFN) is unknown. Data on intermittent or continuous presentation of SFN-related symptoms are also lacking as this is not specifically addressed in the SFN screening list (SFNSL).20 To improve the diagnosis of SSFN, a better understanding of patient-reported symptoms is important, which prompted us to conduct current research. The purpose of this study is threefold. First, we aimed to determine the prevalence of lengthdependent and non-length-dependent patient-reported pain in patients with SSFN. Second, we examined the prevalence of patient-reported intermittent and continuous pain. Finally, we tested whether different diagnostic modalities were associated with specific patient-reported pain presentations (length-dependent, non-length-dependent, continuous or intermittent). Methods Ethics The local Ethics Committee (Medical Research Ethics Committees United, Nieuwegein, the Netherlands R19.080) approved our study. Verbal and written consent was obtained before the start of study. Furthermore, the study was conducted according to the Declaration of Helsinki and GCP guidelines. Design This was a prospective, cross-sectional and observational study, conducted from January 2021 to September 2022 at the outpatient clinic of St. Antonius hospital, a tertiary referral center for sarcoidosis and interstitial lung diseases (ILD) in the Netherlands. Patients with sarcoidosis with symptoms and clinical signs of SFN, aged 18 to 75 years, were included. The guideline of the American Thoracic Society was used for the diagnosis of sarcoidosis.21 Exclusion criteria were large fiber neuropathy, other diseases with a risk for developing (poly)neuropathy or SFN, diseases affecting sensory nerve function, pregnancy, psychological problems, language barrier, glucose intolerance, rheumatoid arthritis, vitamin B12 deficiency, glaucoma, cataract, contact lens wear, anterior chamber angle of the eye below grade 2, keratoconus and excessive alcohol consumption, as assessed by the treating physician. Ophthalmologic assessment An ophthalmologist examined the participants to assess eye involvement in sarcoidosis and general eye condition for exclusion criteria. Glaucoma, keratoconus, and uveitis were assessed by measuring 7 119 7
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