Carpal Tunnel Syndrome Is Associated with Increased Risk of Fibromyalgia: A Retrospective Cohort Study

Background: Carpal tunnel syndrome (CTS) is a common peripheral nerve entrapment disorder with multifactorial etiologies, while fibromyalgia is a chronic centralized pain condition characterized by widespread pain and central sensitization. Although shared mechanisms such as neurogenic inflammation and altered pain processing have been proposed, longitudinal evidence evaluating whether CTS predisposes to subsequent fibromyalgia remains limited. Methods: We conducted a retrospective cohort study using the TriNetX Global Collaborative Network. Adults aged ≥ 18 years with ≥2 clinical encounters between 2018 and 2023 were included. Patients with CTS formed the exposure cohort, while individuals without CTS undergoing routine health examinations served as controls. Those with prior fibromyalgia, malignancy, or death before index were excluded. One-to-one propensity score matching was performed to balance demographics, body mass index, psychiatric conditions, socioeconomic factors, healthcare utilization, and comorbidities including mood, anxiety, stress-related, and sleep disorders. The primary outcome was incident fibromyalgia. Sensitivity analyses included alternative matching strategies, extended washout periods, stricter exposure definitions, and active comparator analyses using osteoarthritis. Stratified analyses by age and sex were conducted. Associations were estimated using hazard ratios with 95% confidence intervals. Results: After matching, 217,208 patients were included in each cohort. CTS was associated with a significantly increased risk of fibromyalgia (HR 2.709, 95% CI 2.521-2.911). Consistent findings were observed across sensitivity analyses. Compared with osteoarthritis, CTS remained associated with higher fibromyalgia risk (HR 1.331, 95% CI 1.254-1.411). Stratified analyses demonstrated consistent associations across age groups (18-64 years: HR 2.820, 95% CI 2.595-3.065; ≥65 years: HR 2.717, 95% CI 2.337-3.159) and sexes (male: HR 3.018, 95% CI 2.482-3.672; female: HR 2.655, 95% CI 2.457-2.869). Conclusions: CTS was associated with coded fibromyalgia diagnosis in this large real-world cohort, and this association was observed across multiple sensitivity and stratified analyses. These findings should be interpreted as evidence of an epidemiologic association rather than a causal relationship. CTS may serve as a clinical marker for patients who warrant attention to broader pain-related symptoms, while future studies are needed to clarify temporality and underlying mechanisms.