Objective: The main objective was to assess the prevalence of fibromyalgia in people with functional motor disorder (FMD) using the 2016 updated diagnostic criteria of the American College of Rheumatology [1]. Additionally, we aimed to examine the differences in clinical characteristics and health related quality of life (HRQoL) between FMD patients with and without comorbid fibromyalgia.

Background: Fibromyalgia is a complex chronic pain disorder characterized by widespread pain, fatigue, cognitive and sleep disturbances, and other symptoms, with a global prevalence estimated at 2-3% [1]. Despite evidence of overlap between FMD and FM [2], the prevalence of fibromyalgia in FMD and its impact on HRQoL remain unclear.

Method: A total of 149 consecutive individuals with clinically established FMD (115 females, mean age 44.6 (SD 11.3) years, mean FMD duration 6.9 (SD 7.3) years) completed a validated questionnaire to assess the presence of fibromyalgia based on predefined cutoffs of the Widespread Pain Index (WPI) and Symptom Severity Score (SSS), along with HRQoL measures. Motor symptoms were classified, and their severity was assessed using the Simplified FMD Rating Scale (S-FMDRS). Using reliable medical reports and detailed evaluations, a multimorbidity index was calculated based on major physical illnesses, neurological comorbidities (including migraine), and psychiatric comorbidities. The use of centrally acting and nociceptive pain medication was also documented.

Results: The prevalence of fibromyalgia was 44.6% (95% CI: 36.2–53.3%). Compared to those without fibromyalgia, patients with fibromyalgia had higher S-FMDRS scores (P=0.004), lower HRQoL (P<0.001), greater use of centrally acting and nociceptive pain medication (P=0.004), and higher multimorbidity index (P=0.048). The sum of WPI + SSS scores weakly correlated with S-FMDRS scores (r=0.20, P=0.019). FMD phenotypes did not differ between those with and without fibromyalgia.

Conclusion: Fibromyalgia was highly prevalent in FMD and was associated with more severe motor symptoms, higher medication use, multimorbidity, and lower quality of life. This finding may have implications for the assessment and management of FMD patients with comorbid pain.

Funding: Supported by the Czech Ministry of Health Grant NW24-04-00456.

References: 1.Wolfe F, Clauw DJ, Fitzcharles MA, et al. 2016 Revisions to the 2010/2011 fibromyalgia diagnostic criteria. Semin Arthritis Rheum 2016;46(3):319-329.
2. Steinruecke M, Mason I, Keen M, McWhirter L, Carson AJ, Stone J, Hoeritzauer I. Pain and functional neurological disorder: a systematic review and meta-analysis. J Neurol Neurosurg Psychiatry. 2024 Aug 16;95(9):874-885.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-prevalence-of-fibromyalgia-in-functional-motor-disorder-a-single-center-pilot-study/