Neuropathic pain features suggestive of small fibre neuropathy in fibromyalgia syndrome: a clinical and ultrasonographic study on female patients.

OBJECTIVES: To evaluate the performance of two screening tools, respectively Pain Detect Questionnaire (PDQ) and Douleur Neuropathique 4 questions (DN4), and the optimal cut-off point of the sural nerve cross-sectional area (CSA), in identifying the neuropathic pain features suggestive of a small fiber neuropathy (SFN), in patients with fibromyalgia syndrome (FM). METHODS: Consecutive adult female FM patients fulfilling the American College of Rheumatology (ACR) 2016 criteria have been enrolled. Patients underwent a clinical assessment and ultrasound examination of the sural nerve CSA. In each patient was established the presence of neuropathic pain features suggestive of the presence of SFN. The performance of PDQ versus DN4 was compared to the clinical judgment of SFN as external criterion analysing the area under the receiver operating characteristic curve (AUCROC). The optimal sural nerve CSA cut-off was established with the ROC curve analysis versus the clinical judgment of SFN. RESULTS: The study involved 80 patients (mean age 49.5±10.5 years, mean disease duration 5.2±4.9 years, mean revised FIQR score 60.9±19.6). Comparing the AUC-ROCs of the screening tools with clinical judgment of SFN, a better AUC was documented, although not significantly (p=0.715), for DN4 (0.875) compared to PDQ (0.857). A sural nerve CSA of 3 mm2 identifies neuropathic pain features with a sensitivity of 70% and a specificity of 90%. CONCLUSIONS: Screening tools have a good concordance in identifying neuropathic pain features suggestive of SFN in FM patients, although a better performance is provided by DN4. Determining the CSA sural nerve with an ultrasound examination may provide some information about the possible presence of SFN.

Sural Nerve Size in Fibromyalgia Syndrome: Study on Variables Associated With Cross-Sectional Area.

Increased cross-sectional area (CSA) of sural nerve, documented by ultrasound (US), has been revealed in small fibers neuropathy, condition present in about half of patients with fibromyalgia (FM). The aims of this study were to evaluate sural nerve CSA and to establish the variables associated with increased CSA in FM patients. A cross-sectional assessment was conducted in consecutive FM patients. Demographic data, clinimetric parameters [Fibromyalgia Impact Questionnaire (FIQR)], the neuropathic pain features [PainDetect Questionnaire (PDQ)], and the sural nerve CSA were recorded. CSA was determined by US, examining the sural nerve at the lateral region of the calf. CSA was compared with demographic and clinical variables. A multiple regression analysis was conducted applying CSA as dependent variable. One hundred and ten FM patients were enrolled. Sural nerve CSA showed a significant association with body mass index (BMI) (r = 0.422; p < 0.0001) and with PDQ (r = 0.361; p = 0.0001). The multiple regression analysis confirmed that BMI (p = 0.0001) and PDQ (p = 0.0028) were the two independent variables associated with CSA. The severity of the disease, measured with FIQR, showed no association. An increase in sural nerve CSA is closely related to BMI and to distinctive neuropathic symptoms. Overweight and obesity appear to be associated with a FM phenotype with documented peripheral nervous system involvement. Ultrasound examination of the sural nerve at calf level may reveal useful information in patients with FM, identifying a cluster of patients with peripheral nervous system alterations. This cluster of patients is generally overweight or obese, and complains of painful symptoms with neuropathic features.