Spectrum of Thyroid Disorders in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory arthritis involving 0.5-1% of the global population. Coexistence of RA and thyroid dysfunction is now increasingly being recognized. This is due to the shared factors involved in the pathogenesis of RA and autoimmune thyroid disease. Thyroid disorder is an important amplifier of disease activity, thereby impairing the quality of life.

To study the prevalence and pattern of thyroid dysfunction in RA patients, to compare the disease activity among RA patients with thyroid dysfunction and those without thyroid dysfunction, and to study the possible association between severe RA and thyroid dysfunction.

A hospital-based analytical cross-sectional study was done in 165 RA patients attending the General Medicine and Rheumatology outpatient facilities of the Department of General Medicine, Government Medical College, Kozhikode, from January to December 2019. Study subjects were selected based on the inclusion and exclusion criteria. Relevant investigations were done, which included serum thyroid stimulating hormone (TSH), free thyroxine (free T4), free triiodothyronine (free T3), and anti-thyroid peroxidase antibody (anti-TPO) antibody levels. Data were analyzed using MS Excel and Statistical Package for the Social Sciences (SPSS) software. The prevalence and pattern of thyroid disorders in RA patients were assessed. The association of thyroid dysfunction with disease activity was tested.

The prevalence of thyroid dysfunction among RA patients was 38.2%. The most common thyroid disorder observed was subclinical hypothyroidism, which was seen in 33.3% (55) of the study population, followed by overt hypothyroidism in 3.6% (6) of patients. Both subclinical hyperthyroidism and clinical hyperthyroidism were found in only 0.6% of RA patients. There was a significant difference in mean age between RA patients with thyroid dysfunction and euthyroid patients (p-value = 0.001). No significant association was found between the duration of RA and thyroid dysfunction (p-value = 0.253). RA patients with thyroid dysfunction had elevated inflammatory markers compared to those with normal thyroid function. The prevalence of autoimmune thyroid disorder in RA patients is 24.8%. There was a significant association between disease activity and thyroid dysfunction (p-value = 0.001). Patients with thyroid disorders had severe disease compared to euthyroid patients. A significant positive correlation was noted between serum TSH and Disease Activity Score-28 (DAS-28) (Pearson coefficient = 0.768, p-value = 0.000), and between anti-TPO antibody and DAS-28 (Pearson coefficient = 0.794, p-value = 0.000).

Thyroid dysfunction is prevalent in 38.2% of RA patients, with subclinical hypothyroidism being the most common thyroid disorder encountered. RA patients with thyroid dysfunction had higher disease activity than euthyroid patients. Hence, thyroid function tests should be a routine investigation in all RA patients, and if found abnormal, they should be treated appropriately.