Background Rheumatoid arthritis (RA) and autoimmune thyroid disease (AITD) tend to cluster together. However the relation between RA autoantibodies and thyroid autoantibodies is debatable.
Objectives To investigate the relation between RA autoantibodies namely anti-cyclic citrullinated peptide (anti –CCP) and rheumatoid factor (RF) and autoimmune thyroid markers [thyroid peroxidase antibodies (anti-TPO), thyroglobulin antibodies (anti-TG) and TSH receptor antibodies (TRAbs)] in RA patients.
Methods The study included 70 RA patients, subclassified according to the presence of RF and anti-CCP into 35 seropositive RA patients (positive to one or both seromarkers), and 35 seronegative RA (negative to both seromarkers). 20 healthy age and sex matched were also included as controls. Detailed history and physical examination focusing on clinical features suggestive of thyroid dysfunction and disease activity score (DAS 28) were assessed. Investigations included measurement of thyroid stimulating hormone (TSH), total triiodothyronine (TT3), total thyroxin (TT4), anti-TPO, anti-TG, and TRAbs in addition to ESR and CRP. Ultrasound neck for assessing thyroid was done in all patients and controls.
Results Hypothyroidism was found in 20/70 (28.57%) RA compared to 15% of controls. Whereas hyperthyroidism was found in 4/70 RA patients (5.71%) compared to 0% of controls. There was no significant difference in thyroid dysfunction between seropositive and negative patients. Mean levels of anti-TPO, anti-TG and TRAbs were significantly higher in RA patients versus controls (p<0. 001). Furthermore, mean anti-TPO was significantly higher in seropositive than seronegative RA (1301. 9±1716. 0 and 799. 4±1597. 7 respectively) (P<0.001). Anti-TG was higher in seropositive than seronegative RA (1750. 0±1866.2 and 898. 1±988. 11 respectively) (P<0.001). Similarly, TRAbs were significantly higher in seropositive than negative RA (p=0. 006). Ultrasonographic thyroiditis was significantly evident in RA patients versus control (p=0.001) with no difference between seropositive and negative RA. Significant positive correlation was found between RA autoantibodies (RF and anti-CCP) and thyroid autoantibodies in seropositive patients.
Conclusions Thyroid dysfunction and AITD are common in RA patients, with hypothyroidism being the commonest regardless of RA serostatus and disease activity assessed by DAS 28.
Seropositivity to RF and/ or anti-CCP infers a state of increased immune reactivity in RA as evidenced by the significantly higher levels of all thyroid autoantibodies in seropositive patients than seronegatives and controls and by the positive correlation between the RA autoantibodies and thyroid autoantibodies. Accordingly, screening for thyroid autoantibodies in RA patients especially seropositives is recommended.
Disclosure of Interest None declared
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