Frequency of rheumatoid arthritis in patients with autoimmune thyroid disease: a case–control study

Introduction Hashimoto’s thyroiditis and Graves’ disease both constitute autoimmune thyroid diseases (AITD) that frequently coexist with other autoimmune disorders (AID). This study was conducted to evaluate the frequency of rheumatoid arthritis (RA) in patients diagnosed with AITD in relation to the general population. Patients and methods This was a cross-sectional case–control study, conducted on 103 patients with AITD of either Hashimoto’s thyroiditis or Graves’ disease with positive antithyroid peroxidase (TPOAb). A group 100 volunteers, matched for age and sex, with normal thyroid function and negative history of AID, were investigated for the prevalence of RA in the general population (control group). Participants in the study were tested for thyroid profile, rheumatoid factor (RF), erythrocyte sedimentation rate, and C-reactive protein. When appropriate, anticitrullinated peptide antibody was checked. Results Patients with AITD had a higher frequency of RA than the control (P=0.031). Thyroid profile showed no significant difference between patients with and without RA within the group of AITD. In that group, a positive correlation between titers of both RF and TPOAb was observed (r=0.474, P<0.001). The coexistence of RA with AITD was noticed to be associated with higher RF, C-reactive protein, and TPOAb titers as well as. the presence of type 2 diabetes mellitus, other AID and family history of RA. Conclusion RA is more prevalent in patients with AITD than the general population, and the underlying autoimmunity is likely to be the link. Our data highlight the importance of screening thyroid patients for RA especially if present with type 2 diabetes mellitus, another AID, or having a family history of RA.