Objective. Some studies have reported the presence of histological alterations, such as myofiber disorganization and
abnormalities in the number and shape of mitochondria, in patients with fibromyalgia syndrome (FMS). Although
Ultrasound imaging (US) is used to quantitatively characterize muscle tissues, US studies in patients with FMS are
lacking. Therefore, we aimed to describe morphological and qualitative cervical multifidus (CM) muscle US features
in women with FMS and to assess their correlation with clinical indicators. Design. Observational study. Setting.
AFINSYFACRO Fibromyalgia Association (Madrid, Spain). Subjects. Forty-five women with FMS participated.
Methods. Sociodemographic variables (e.g., age, height, weight, body mass index) and clinical outcomes (e.g., pain
as assessed on a numerical pain rating scale, evolution time, pain-related disability as assessed by the Fibromyalgia
Impact Questionnaire) were collected. Images were acquired bilaterally at the cervical spine (C4–C5 level) and mea sured by an experienced examiner for assessment of muscle morphology (e.g., cross-sectional area, perimeter, and
shape) and quality (mean echo intensity and intramuscular fatty infiltration). Side-to-side comparisons and a correla tional analysis were conducted. Results. No significant side-to-side differences were found for morphology or quality
features (P > 0.05). None of the clinical indicators were associated with US characteristics (all, P > 0.05). Conclusion.
Our results showed no side-to-side differences for CM morphology and quality as assessed with US. No associa tions between CM muscle morphology or quality and Fibromyalgia Impact Questionnaire, pressure pain threshold,
numerical pain rating scale score, or evolution time were observed. Our preliminary data suggest that muscle mor phology is not directly related to pain and pain-related disability in women with FM