The prevalence of thyroid dysfunction and autoimmune thyroid disease in patients with rheumatoid arthritis

Background Rheumatoid arthritis (RA) is one of the most common chronic non-organ-specific autoimmune diseases; meanwhile, autoimmune thyroid disease (AITD) is the most common organ-specific autoimmune disease that can lead to hypo or hyperthyroidism. Although the etiology of both diseases is complex with a combination of genetic and environmental factors, there are overlaps in genes contributing to the pathogenesis of both diseases. Numerous studies found a correlation between thyroid abnormality and RA in different populations, yet some didn't. This study is aimed to evaluate the prevalence of thyroid dysfunction, AITD, and anti-thyroid peroxidase (anti-TPO) positively in Iranian patients with RA. Methods A total of 250 RA patients and 248 patients with non-inflammatory rheumatologic disease were included in this case-control study. All participants underwent complete clinical and laboratory assessments. Participants were also assessed for thyroid function testing, including anti-TPO antibodies. Results Thyroid dysfunction was twice as common in RA patients as in controls (OR = 2.16; P-value > 0.001). Overt hypothyroidism was the most common thyroid dysfunction among RA patients (58 out of 84). Anti-TPO positivity was also significantly more common in RA compared with controls (OR = 2.65; P-value > 0.001). The proportion of controls and RA patients with AITD were 9 and 21.5%, respectively. AITD was found 2.8 times more common in RA group than controls (OR = 2.77; P-value > 0.001). Conclusion It was demonstrated that RA was an independent factor associated with thyroid dysfunction and AITD. Keywords: Rheumatoid arthritis, RA, Thyroid dysfunction, Anti-thyroid autoantibody, Anti-TPO, Autoimmune thyroid disease, AITD, Thyroid hormone abnormality