Imaging of the peripheral nervous system in nociplastic pain: An ultrasound study in patients with fibromyalgia

Background and Purpose: Although fibromyalgia (FM) is considered a central sensitization syndrome, studies investigating peripheral nerves in this condition are not available. The primary objective of this study is to investigate the sonographic changes (ie, increased cross sectional area [CSA]), of peripheral nerves in patients with FM compared to healthy controls. The secondary objective is to identify potential clinical correlations associated with increased CSA in patients with FM. Methods: In this cross-sectional observational study, consecutive female patients with FM underwent sonographic assessment using a standardized scanning protocol. The CSA of seven nerves was measured bilaterally at 11 anatomic sites by an experienced sonographer. Differences in CSA of nerves were compared with those of healthy subjects by one way analysis of variance. Patients underwent clinimetric evaluation aimed at investigating disease severity, neuropathic pain features, depression, anxiety, fatigue, and autonomic symptoms to explore the possible correlation between CSA and clinical features. Results: Forty-seven patients and 20 healthy controls were enrolled. Differences in terms of increased CSA between patients and healthy controls were identified at multiple levels, mainly at the level of the sural nerve, vagus nerve, and sixth cervical nerve root (for all, p< .001). Sonographic findings, however, did not correlate with the clinical features explored. Conclusions: Patients with FM show higher CSA of nerves than healthy subjects. The increased CSA is most evident at the sural nerve, vagus nerve, and sixth cervical nerve root. Ultrasound, a relatively easy-to-use technique, could identify morphological changes, in peripheral nervous structures in patients with FM.