Hypothalamus-hypophysis-thyroid axis, triidothyronine and antithyroid antibodies in patients with primary and secondary Sjogren's syndrome

It has been well established that, antithyroglobulin antibodies (ATG) and anti-microsomal antibodies (AMC) may be present in various thyroid disorders and other systemic autoimmune diseases, including Sjogren's syndrome (SS). However, presence of circulating autoantibodies to thyroid hormones, i.e. both to triiodothyronine (T3) and tetraiodothyronine (T4), has not been studied extensively in SS. Autoantibodies to T3 and T4 are very important, because serum T3 and T4 levels may be detected spuriously higher or lower, due to the presence of these autoantibodies. Their presence should be suspected when measured serum thyroid hormone levels are not consistent with clinical status of the patient. SS is a slowly progressive, inflammatory autoimmune disease, affecting primarily the exocrine glands. Thyroid gland, being a target in some autoimmune diseases, is well known to be affected in SS as well. Keeping this possibility in mind, we investigated T3 autoantibody levels and thyroid gland involvement in patients with SS. Twenty-six SS patients (F/M:22/4) with a mean age of 46,6 years, were recruited in this study. Twelve of them we-re accepted as primary SS (pSS), while others had secondary SS (sSS) (7 with rheumatoid arthritis (RA), 3 with systemic lupus erythematosus (SLE), 3 with progressive systemic sclerosis (PSS) and 1 with sarcoidosis). Thyroid function tests, including T3, T4, fT3, fT4, TSH, ATG, AMC, T3 antibody measurements, thyroid scintigraphy, thyroid ultrasonography and TRH stimulation tests were performed in all patients. We compared our results with those of the twenty healthy normal controls. Serum ATG and/or AMC were detected in three patients with pSS (25%) and no patients with sSS. No significant difference could be shown in the other parameters, including T3 autoantibodies and thyroid function tests. TRH stimulation test was also normal, showing that the hypothalamus-hypophysis-thyroid axis was not affected in patients both with pSS and sSS. In conclusion, we found that T3 autoantibody levels in pSS, were not significantly higher than sSS and normal controls.