Relationship between thyroid stimulating hormone and thyroid stimulating immunoglobulin in Graves’ hyperthyroidism

Abstract

Background and Aim: In Graves’ hyperthyroidism, suppression of serum TSH after restoration of normal serum T₄ and T₃ with treatment has been attributed to binding of TSH-receptor antibodies to TSH receptors in the pituitary. Accordingly, the relationship between TSH and serum thyroid stimulating immunoglobulin (TSI) was examined during follow-up of patients with Graves’ hyperthyroidism. Subjects and Methods: 23 patients with Graves’ hyperthyroidism were identified who met the inclusion criteria of at least 24 months follow-up after initiation of methimazole and availability of concurrent measurements of serum TSH and TSI. Results: TSI disappeared in 12 patients (Group A) and persisted in 11 patients (Group B). Initial T₄ was not significantly different between the 2 groups. However, TSI was significantly lower in Group A than Group B [median (interquartile range) 179 (152–212)% vs 255 (208–369)%, p=0.0009]. In Group A, TSH normalized during treatment, and this anteceded disappearance of TSI by a significant time interval [median (interquartile range) 6 (3–8) months vs 15 (11–20) months, p=0.005]. In Group B, TSI persisted in all patients during follow-up ranging from 24 to 73 months. No correlation was found to exist between serum TSH and TSI, and for Group B TSI at final follow-up was not significantly different from the initial value [median (interquartile range) 255 (208–369)% vs 236 (160–310)%, p=0.4]. Conclusions: These findings do not support the suggestion that TSI has a direct suppressive effect on TSH secretion.