Autoimmune Thyroid Disease and Sjögren Disease: Organ-Specific Disease Triggered by Systemic Autoimmunity?

<i>Background and Objectives</i>: Autoimmune thyroid diseases are more prevalent in patients diagnosed with Sjögren disease (SD) than in the general population. SD and autoimmune thyroid diseases are two distinct yet interrelated autoimmune disorders. The objective of this study was to determine the frequency of autoimmune thyroiditis (AT), autoantibody relationships, and clinical features in patients with SD. <i>Materials and Methods:</i> The study included 525 patients. A retrospective evaluation was conducted on the demographic data, biochemical and serological tests, and pathological data of the patients. An anti-nuclear antibody (ANA) test was performed using the indirect immunofluorescence (IIF) method using HEp-2 (HEp-2000) cells as substrate. The Schirmer test and minor salivary gland biopsy were conducted on all patients. <i>Results:</i> AT was detected in 167 (31.8%) of 525 patients who participated in the study. The anti-nuclear antibody (ANA) test and anti-SS-A positivity rate were higher in the AT group (<i>p</i> value < 0.001 and 0.002 respectively). We found that the likelihood of developing AT increased as ANA titres increased. ANA positivity titres were found to be significant at 2+, 3+, and 4+ values (odd ratios 2.41, 3.40, and 4.21, respectively). Additionally, histological examination of salivary gland biopsies revealed a significantly higher prevalence of diffuse lymphocytic infiltration in the AT group. <i>Conclusions:</i> AT was present in 31% of patients with SD. The presence of ANA positivity, anti-SS-A positivity, and diffuse lymphocytic infiltration appears to exert an influence on the association between these two diseases.