The association between thyroid dysfunction, autoimmune thyroid disease, and rheumatoid arthritis disease severity

Background Rheumatoid Arthritis (RA) and autoimmune thyroid disease (AITD) are the two most prevalent coexisting autoimmune diseases due to their similar pathogenesis. Considering the potential effect of AITD on the severity of RA disease, this study aimed to determine the association between thyroid dysfunction, anti-thyroid peroxidase (anti-TPO) positivity, AITD, and RA disease severity in the Iranian population. Methods Three hundred and fifty RA patients who presented to Shahid Beheshti tertiary care center, Qom, Iran, were included in this cross-sectional study. The data were collected through the patient’s medical records, interviews, physical examinations, and laboratory tests. The RA disease activity score in 28 joints for RA with erythrocyte sedimentation rate (DAS-28-ESR) was used to divide patients into three subgroups, remission (DAS-28-ESR ⩽ 2.6), mild-to-moderate (2.6 < DAS-28-ESR ⩽ 5.1), and severe disease activity (DAS-28-ESR > 5.1). Results Using the aforementioned method, 111, 96, and 138 patients were put into remission, mild-to-moderate, and severe disease activity groups, respectively. Anti-TPO antibody positivity rate was 2.93 times more prevalent among patients with severe disease compared to the remission subgroup (OR: 2.93; P-value < 0.001). Patients suffering from a more severe disease were almost 2.7 times more probable to have AITD (OR = 2.71; P-value < 0.001) and they were 82% more likely to have thyroid dysfunction compared to patients in remission (OR = 1.82; P-value = 0.006). Conclusions It was demonstrated that thyroid dysfunction, anti-TPO antibody positivity, and AITD were significantly more common among RA patients with more severe disease activity.