THU0477 SURAL NERVE SIZE IN FIBROMYALGIA SYNDROME
Authors: M. DI Carlo, C. Ventura, P. Cesaroni, M. Carotti, A. Giovagnoni, F. Salaffi
Journal: Annals of the Rheumatic Diseases (2020)

Background: The pathophysiology of fibromyalgia syndrome (FM) still needs to be fully clarified. In addition to the central sensitization mechanisms, some evidence suggests an involvement of the peripheral nervous system, mainly intended as small fibers neuropathy. The sural nerve showed some alterations, in terms of increasead cross-sectional area (CSA), in the course of small fibers neuropathy. Objectives: To evaluate sural nerve CSA and factors associated with increased CSA in FM patients. Methods: A cross sectional evaluation was conducted in consecutive FM patients according to the 2016 American College of Rheumatology criteria. Demographic, clinimetric parameters (in particular the revised Fibromyalgia Impact Questionnaire [FIQR] to assess the severity of the disease and the PainDetect Questionnaire [PDQ] to evaluate neuropathic pain features) and the sural nerve dimensions measured by ultrasound were recorded for each patient. The size of the sural nerve was described in terms of the mean cross-sectional area (CSA) measured bilaterally. CSA was measured at the leg level, 14 cm from the apex of the lateral malleolus, where the sural nerve is detectable as a structure adjacent to the small saphenous vein in the distal portion of the leg. The ultrasound examination was performed with a MyLab Class C (Esaote S.p.A., Genoa, Italy) equipped with a 6-18 MHz multifrequency broad band probe. CSA was compared with demographic and clinimetric parameters through one-way analysis of variance (ANOVA). A multiple regression was also conducted using CSA as dependent variable, with age, body mass index (BMI), disease duration, FIQR and PDQ as independent variables. Results: The study involved 110 FM patients (105 women and five men), with a mean age of 50.7 (±11.1) years and a mean disease duration of 5.8 (±5.2) years. Sural nerve CSA showed a statistically significant increase in patients with higher PDQ scores (p=0.0096) and, even more significantly, in overweight or obese subjects (p &lt;0.001). The multiple regression analysis, using CSA as dependent variable, confirmed that the PDQ score (p=0.0049) and the body mass index (p&lt;0.0001) are the only two independent variables associated with CSA size (Table 1). Table 1. Multiple regression analysis of the independent variables related to the mean cross-sectional area (dependent variable) of sural nerve. Indipendent variables Coefficient Standard error t p r partial r semipartial Constant -0.2551 BMI 0.07592 0.01847 4.111 0.0001 0.3739 0.3462 Disease duration -0.02492 0.02092 -1.191 0.2364 -0.1160 0.1003 Age 0.002455 0.009833 0.250 0.8033 0.02448 0.02103 FIQR 0.0001376 0.006862 0.0201 0.9840 0.001966 0.001689 PDQ 0.05272 0.01997 2.639 0.0096 0.2506 0.2223 Abbreviations: BMI=Body Mass Index; FIQR=revised Fibromyalgia Impact Questionnaire; PDQ=PainDetect Questionnaire Conclusion: Increased sural nerve CSA is associated with neuropathic like pain features and BMI. Overweight and obesity appear to be associated with an FM phenotype with greater peripheral involvement than normal-weight subjects. Sural nerve ultrasound, an easy to perform examination, could be a useful tool to identify this kind of patients. References: [1]Ebadi H, Siddiqui H, Ebadi S, Ngo M, Breiner A, Bril V. Peripheral Nerve Ultrasound in Small Fiber Polyneuropathy. Ultrasound Med Biol. 2015;41(11):2820-6. doi: 10.1016/j.ultrasmedbio.2015.06.011 [2]Giannoccaro MP, Donadio V, Incensi A, Avoni P, Liguori R. Small nerve fiber involvement in patients referred for fibromyalgia. Muscle Nerve. 2014;49(5):757-9. doi: 10.1002/mus.24156 Disclosure of Interests: : None declared