Prevalence and pattern of coexisting autoimmune diseases among patients with autoimmune thyroid disease in Al-Qassim Region, Saudi Arabia: a retrospective cross-sectional study

Objective: This study aimed to determine the prevalence and pattern of coexisting autoimmune diseases among patients diagnosed with Hashimoto's thyroiditis or Graves' disease, and also to explore associations between demographic and clinical factors and their presence. Methods: A retrospective cross-sectional study was adopted to review medical records of 301 patients with confirmed autoimmune thyroid diseases (AITDs) in King Fahd Specialist Hospital (KFSH) in the Al-Qassim region, Saudi Arabia. Results: A total of 301 patients with AITDs were included, with a mean age of 40.7 years. Notably, 84.4% were female, and 87.7% had Hashimoto's thyroiditis. Overall, 122 patients (prevalence of 40.5% with 95% CI of 35.1â€"46.2%) had at least one coexisting autoimmune disease. The prevalence was significantly higher among patients with Hashimoto's thyroiditis than Graves' disease (p-value≤0.001). Rheumatoid arthritis (19.7%), type 1 diabetes mellitus (15.6%), and vitiligo (14.8%) were the most common coexisting autoimmune diseases. Multivariable analysis identified male gender (aOR≤2.09, p-value≤0.025) and Hashimoto's thyroiditis (aOR≤4.61, p-value≤0.002) as independent predictors of coexisting autoimmune disease. Conclusion: Coexisting autoimmune diseases were common among patients with autoimmune thyroid disease, particularly those with Hashimoto's thyroiditis. Rheumatoid arthritis, type 1 diabetes mellitus, and vitiligo were the predominant comorbidities.