Endocrine Comorbidities in Fibromyalgia

Background: Fibromyalgia (FM) is a chronic pain syndrome increasingly linked to immune and endocrine dysfunction. This study aimed to evaluate the prevalence of endocrine comorbidities in FM patients compared to matched controls using a large healthcare database. Methods: A population-based case-control study was conducted using data from Leumit Health Services, Israel. The cohort included 9,232 adults diagnosed with FM according to ACR criteria, matched by age and sex to 46,160 control subjects. Endocrine disorders were identified via ICD-9 codes. Statistical analyses included Student's t-test or Mann–Whitney U test for continuous variables, Pearson's chi-squared or Fisher's exact test for categorical variables, and multivariable logistic regression adjusting for age, sex, and BMI. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Both statistical significance and effect sizes are reported to facilitate assessment of clinical relevance. Results: FM patients showed a significantly higher prevalence of endocrine comorbidities compared to controls. Thyroid disorders, including Hashimoto's thyroiditis (13.3% vs. 10.0%; OR = 1.38, p < 0.001) and Graves' disease (4.1% vs. 3.0%; OR = 1.38, p < 0.001), were more common. Diabetes mellitus type 1 (0.9% vs. 0.3%; OR = 3.64, p < 0.001) and type 2 (23.5% vs. 18.6%; OR = 1.34, p < 0.001), adrenal disorders such as Cushing's syndrome (OR = 5.01, p < 0.001), prolactinoma (OR = 1.81, p = 0.014), osteoporosis (19.1% vs. 11.6%; OR = 1.80, p < 0.001), and vitamin D deficiency (39.9% vs. 30.3%; OR = 1.53, p < 0.001) were also significantly associated. Less common conditions (e.g., thyroiditis subtypes and thyroid malignancy) also appeared more frequent among FM patients, though effect sizes varied and some associations did not reach robust significance. Conclusion: This is among the largest datasets to date to systematically examine a comprehensive spectrum of endocrine comorbidities in FM. Our findings suggest that FM and endocrine disorders may share overlapping pathophysiological mechanisms. Future studies should clarify causal pathways and assess the clinical utility of routine endocrine screening in FM patients.