New-Onset Chronic Musculoskeletal Pain Following COVID-19 Infection Fulfils the Fibromyalgia Clinical Syndrome Criteria: A Preliminary Study

New-onset chronic musculoskeletal (MSK) pain (>3 months duration) is a common symptom of post-COVID-19 syndrome (PCS). This study aimed to characterise new-onset chronic MSK pain in patients with PCS and its overlap with Fibromyalgia Syndrome (FMS). We enrolled patients with new-onset chronic MSK pain post-COVID-19 and assessed the nature of the pain and associated symptoms using the C19-YRS (Yorkshire Rehabilitation Scale). The FMS assessment was conducted as part of a standard clinical examination using the American College of Rheumatology (ACR) 2010 criteria: (1) Widespread Pain Index (WPI) ≥ 7 and symptoms severity (SS) score ≥ 5, or WPI between 3 and 6 and SS score ≥ 9, (2) symptoms consistent for at least 3 months, and (3) no alternative diagnosis. Of the eighteen patients (average age 49.6 (SD 11.8) years; BMI 31.7 (SD 8.6)), twelve were female. The average symptom duration was 27.9 (SD 6.97) months post-infection. Thirteen patients (72.2%) met the FMS criteria, with an average WPI score of 8.8 and an average SS score of 8.2, indicating a high level of pain and significant quality of life impacts. These findings support the hypothesis that FMS may develop as a long-term sequela of a viral infection, underscoring the need for further research into post-viral long-term conditions.