The relationships between serum T3 index, thyroid volume, and thyroid stimulating, TSH receptor binding and thyroid growth stimulating antibodies in untreated Graves' disease

In Graves' disease, thyroid autoantibodies and ultrasound features correlate with distinctive histological features

PURPOSE

Laboratory, imaging, and pathological features of Graves' disease (GD), although well characterized, have been barely correlated each other. Aim of the study was to link laboratory and ultrasound characteristics of GD with its pathological features.

METHODS

We correlated laboratory and ultrasound data at the time of diagnosis in 28 consecutive GD patients who underwent thyroidectomy with their pathological features, i.e., lymphocytic infiltration and follicular hyperplasia (both classified as mild or severe).

RESULTS

Thyroid volume correlated positively with the levels of FT4 (P = 0.002, r² = 0.42), FT3 (P = 0.011, r² = 0.22), autoantibodies to thyroglobulin (TgAbs) (P = 0.016, r² = 0.32), autoantibodies to thyroid peroxidase (TPOAbs) (P = 0.011, r² = 0.34) and the extent of lymphocytic infiltration (P = 0.006 comparing mild to severe lymphocytic infiltration) but not with the levels of autoantibodies to the thyrotropin receptor (TRAbs) and to follicular hyperplasia. Compared to subjects with mild lymphocytic infiltration, those with severe lymphocytic infiltration showed higher levels of TgAbs (316 vs 0.0 IU/mL, P < 0.0001) and TPOAbs (295 IU/mL vs 14 IU/mL, P < 0.0001) and similar levels of TRAbs (7.5 vs 13 IU/mL, P = 0.68). Compared to patients with mild, those with severe follicular hyperplasia had similar levels of TgAbs (76 vs 30 IU/mL, P = 0.31) and TPOAbs (251 IU/mL vs 45 IU/mL, P = 0.26) but higher levels of TRAbs (39 vs 7.2 IU/mL, P < 0.001).

CONCLUSION

In GD, TgAbs and TPOAbs levels correlate with the extent of lymphocytic infiltration, TRAbs levels with the degree of follicular hyperplasia. Thyroid volume, the main factor influencing the severity of hyperthyroidism, is related to lymphocytic infiltration and not to follicular hyperplasia.

Treatment of Graves' hyperthyroidism: evidence-based and emerging modalities

Currently there are three well-established treatment options for hyperthyroid Graves' disease (GD): antithyroid drug therapy with thionamides (ATD), radioactive iodine treatment with (131)I, and thyroid surgery. This article reviews the current evidence so the reader can evaluate advantages and disadvantages of these treatment modalities. Surgery is rarely used, except for patients who have a large goiter or ophthalmopathy. Fewer than 50% of patients treated with ATD remain in long-term remission. Therefore, radioactive iodine is used increasingly. No data as yet support the routine use of biologic therapies (eg, rituximab). Prospective, randomized studies comparing available and any novel therapeutic options for GD are needed. The focus of these studies should include, but not be limited to, cost and quality of life.

Anti-TSH receptor antibodies in clinical practice

Anti-thyroid stimulating hormone receptor antibodies are pathophysiologic and clinical indicators in autoimmune thyroid diseases, not only in Graves' disease. The detection of these antibodies is useful for diagnostic and management purposes. The presence and titers of anti-TSH receptor antibodies, however, have to be interpreted in light of the clinical and other biological characteristics of each patient. Newer, more sensitive assays of anti-TSH receptor antibodies may increase their significance in the diagnosis and management of autoimmune thyroid diseases and Graves' disease.

Heterogeneity of circulating TSH-receptor antibodies in thyroid disease demonstrated directly by chromatography

The heterogeneity of circulating TSH-receptor antibodies (TRAb) has been demonstrated directly by affinity chromatography on the dye Remazol Yellow-GGL. The technique resolved these antibodies into discrete peaks within the general serum immunoglobulin background. Peaks were detected initially by a binding (radioreceptor) assay and then characterized by their ability to stimulate the uptake of iodine-125 into FRTL-5 cells. Thirteen subjects with high serum levels of TRAb were studied. The two hypothyroid patients each produced a single peak of TRAb activity with no ability to stimulate uptake of iodine-125 into cultured cells. The remaining 11 patients had Graves' disease; their sera produced a range of elution profiles after chromatography with TRAb activity resolved into as many as five peaks. Considerable differences were seen in the relative abilities of the resolved TRAb components to bind to receptors and to stimulate cellular uptake of iodine-125 both between and within individual samples. No two patients produced components which chromatographed in the same position on the gradients employed for elution from the dye.

Thyroid autoimmunity in endemic goitre caused by excessive iodine intake

The pathophysiology of endemic goitre caused by excessive iodine intake is not well defined. By interacting with the immune system, iodine excess may trigger the development of autoimmune thyroid disease such as lymphocytic Hashimoto's thyroiditis (LT). In an attempt to examine this further, we compared the presence of thyroid autoantibodies in 29 goitrous children, from an iodine excess area, and in 26 healthy children, from an iodine sufficient area, of north central China. Serum was tested for antimicrosomal (MAb), anti-thyroglobulin (TgAb), second colloid antigen antibodies (CA2-Ab) and TSH binding inhibitory immunoglobulins (TBII). Affinity chromatographically purified IgG was tested for thyroid growth-stimulating activity (TGI) by two different methods: a sensitive cytochemical bioassay (CBA) using guinea-pig thyroid explants and a mitotic arrest assay (MAA) employing a continuous rat thyroid cell line (FRTL-5). We found no increased prevalence of LT in patients with endemic iodine goitre. The levels of MAb, TgAb and CA2-Ab did not differ significantly between the two groups of children. Further, TBII were not present in either group. Thyroid growth-stimulating immunoglobulins (TGI) were the major autoantibodies found in children with goitres caused by iodine excess. In the CBA, 12 of 20 (60%) goitrous children and 0 of 12 (0% P less than 0.05) healthy children were positive for TGI. Similar results were found in the MAA, and a good correlation between results of the CBA and MAA was found (P = 0.003). Maximal TGI activity in dose-response CBA showed a good relation with clinical goitre size (r = 0.63; P less than 0.05) indicating a possible pathophysiological role for these antibodies. We conclude that endemic iodine goitre is not associated with Hashimoto's lymphocytic thyroiditis. Nevertheless, autoimmune growth factors such as TGI may play a primary role in the pathogenesis of thyroid growth in this condition.

Evaluation of TSH receptor antibody by 'natural in vivo human assay' in neonates born to mothers with Graves' disease

Neonatal thyrotoxicosis induced by transferred TSH receptor antibody (TRAb) is the ideal human in-vivo experimental system for the evaluation of TRAb. The clinical significance of circulating TRAb in Graves' disease was evaluated by this 'natural in-vivo human assay'. TRAb activity in vitro was measured by radioreceptor assay (thyrotrophin-binding inhibitor immunoglobulin, TBII) and sensitive cAMP accumulation assay using FRTL-5 cells (thyroid-stimulating antibody, TSAb). Further, the binding-stimulation index (B-S index) was newly introduced, which was the most useful indicator for prediction of neonatal thyrotoxicosis, calculated as the product of TBII and TSAb (Tamaki et al., 1988a). Maternal serum TRAb indices showed highly significant correlations with the serum free T4 index (FT4I) and free T3 index (FT3I) in neonates (5-10 days after birth) born to 20 mothers with Graves' disease who had positive TBII and/or TSAb (FT4I: r = 0.825 for TBII, r = 0.908 for TSAb, r = 0.944 for the B-S index, P less than 0.001; FT3I: r = 0.622 for TBII, P less than 0.01, r = 0.812 for TSAb, r = 0.791 for the B-S index, P less than 0.001; n = 20). In contrast, in 57 untreated adult patients with hyperthyroid Graves' disease, the FT4I and FT3I levels were not correlated with any of the TRAb indices. The linear regression relationship between the B-S index and FT4I found in neonates was applied to values in adult patients with Graves' disease, and the patients were divided into three groups on the basis of the 95% confidence limit: high, normal, and low responders of thyroid hormone (FT4I) secretion to the B-S index. FT4I and the ratio of FT4I to the B-S index were highest and the TRAb indices were lowest in the high responders, while FT4I and the FT4I/B-S index ratio were lowest and the TRAb indices were highest in the low responders. The FT4I/B-S index ratio was inversely correlated with the titres of antithyroid microsomal antibody in all the adult patients with untreated Graves' disease (r = -0.288, P less than 0.05). The results suggest that in-vitro assays using animal thyroid cells and cAMP as an index of response are suitable for detecting circulating thyroid stimulating activity in vivo. Secretion of thyroid hormones in Graves' disease may be regulated not only by circulating thyroid-stimulating antibodies but also by intrathyroidal stimulatory factors or by inhibitory or destructive factors.