Objectives: We investigated the prevalence of anti-thyroid autoantibodies and thyroid dysfunction, and their association with clinical and laboratory features in Korean patients with primary Sjögren's syndrome (pSS) without overt thyroid illnesses.
Methods: We consequently included 196 pSS patients (190 women) and cross-sectionally collected clinical and laboratory data including the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) and Patient Reported Index (ESSPRI). The fatigue-dominant group was defined as those in the highest quartile of the fraction of fatigue, calculated as the ESSPRI fatigue score divided by the total ESSPRI score. Thyroid stimulating hormone (TSH), free T4 (fT4), anti-thyroglobulin (TG), anti-thyroid peroxidase (TPO), and anti-TSH receptor antibody (TRAb) were measured.
Results: Of 196 patients, 31 (15.8%) were positive for anti-TG, 28 (14.3%) for anti-TPO, and 28 (14.3%) for TRAb. Subclinical hypothyroidism (S-Hypo) was identified in 23 (11.7%) patients. Anti-TG had no correlations with thyroidal function or pSS-related features. Meanwhile, anti-TPO was significantly associated with TSH levels or anti-centromere antibody. TRAb-positive patients exhibited significantly higher ESSDAI and clinical ESSDAI scores. Moreover, the most influential independent predictor for TRAb was lymphopenia (odds ratio [OR] = 5.541), which has been known as a prognostic factor. Additionally, significant bidirectional associations were found between the fatigue-dominant group (OR = 3.482) and anti-TPO-positive S-Hypo (OR = 7.586) in multivariate regression analyses.
Conclusions: Latent thyroid autoimmunity, particularly TRAb and anti-TPO, may be associated with clinical and laboratory manifestations of pSS, such as disease activity or fatigue, even without overt thyroid dysfunction.