Background According to the common notions, rheumatoid arthritis (RA) is an immunopathological condition with complex autoimmune response, directed presumably to synovial tissue. Besides that, there are some organ involvements in RA, that can strongly affect the extent of the autoimmune reactions. One of this organs is thyroid gland, because changes of its function, either increase or decrease, modulate activity of immune cells and inflammation level on the whole. Production of antibodies, directed to T3 and T4, is a candidate mechanism of the thyroid involvement.
Objectives The objectives of our study are detection of different thyroid conditions in RA including determination of lesion type and function assessment, as well as searching for interdependence between the clinical features of RA, type of thyroid involvement, and the level of the anti-hormonal antibodies.
Methods The research was carried out in agreement with the principles of the World Medical Association Declaration of Helsinki (1997). Approval for the investigation was got from the Regional Medical Ethics Committee. We enrolled adult patients with RA, verified using ACR/EULAR criteria (2010). RA activity was determined by means of DAS28 index. Thyroid involvement was detected by clinical, ultrasound, and laboratory assessment, including TSH, free T3, free T4, and anti-TPO. Anti-T3 and anti-T4 antibodies were measured using ELISA and calculated in terms of optical density units (ODU). The positive cutoff values, 0.098 ODU for anti-T3 and 0.093 ODU for anti-T4, have been found using healthy controls (n=39). Results were expressed as means±standard errors, the differences were considered significant at p<0.05.
Results 75 patients with RA have been enrolled, including 61 (81.4%) women and 14 (18.6%) men, their age was from 25 to 78 years. Mean RA activity was 3.2±1.4 DAS28 points. Different visceral involvements were detected in 20 (26.7%) cases, and 5 (6.7%) of them had an overt clinical picture of thyroid lesions. The signs and symptoms for 4 of them were similar to Hashimoto's thyroiditis with hyperfunction, the remaining one was complied to the mixed toxic goiter. All these 5 patients had low TSH and quite high DAS28 score (4.8±1.9). However, the prevalence of subclinical thyroid disorders in RA was considerably higher. Virtually all the patients (n=73) have been revealed anti-T3 (0.128±0.047 ODU) and/or anti-T4 antibodies (0.152±0.050 ODU). There was no relationship between these antibodies and organ involvement, other than thyroid gland; RF titers also had no significant influence. We found some rather unexpected dependencies of these markers with X-ray RA stages, as well as with RA activity. There was a clear trend of elevation of mean anti-T4 concentration together with higher Steinbrocker stage (p=0.034, ANOVA), the inverse tendency have been observed for anti-T3 (p=0.047, ANOVA). Correlations of DAS28 score with anti-T4 (r=0.525, p=0.031) and anti-T3 (r=-0.391, p=0.040) were also opposite. There was another significant inverse correlation of DAS28 score and TSH concentration (r=-0.330, p=0.046).
Conclusions Our data suggest that though anti-T4 concentration is tended to be elevated, high RA activity can promote hyperthyroidism. This is probably due to either influence of these antibodies to T4 and T3 production, or immune disturbances caused by thyroid hyperfunction itself.
Disclosure of Interest None declared