High prevalence and little change in TSH receptor blocking antibody titres with thyroxine and antithyroid drug therapy in patients with non-goitrous autoimmune thyroiditis

Non-Conventional Clinical Uses of TSH Receptor Antibodies: The Case of Chronic Autoimmune Thyroiditis

Anti TSH receptor antibodies (TSHrAb) are a family of antibodies with different activity, some of them stimulating thyroid function (TSAb), others with blocking properties (TBAb), it is a common finding that antibodies with different function might coexist in the same patient and can modulate the function of the thyroid. However, most of the labs routinely detect all antibodies binding to the TSH receptor (TRAb, i.e. TSH-receptor antibodies detected by binding assay without definition of functional property). Classical use of TSHr-Ab assay is in Graves' disease where they are tested for diagnostic and prognostic issues; however, they can be used in specific settings of chronic autoimmune thyroiditis (CAT) as well. Aim of the present paper is to highlight these conditions where detection of TSHr-Ab can be of clinical relevance. Prevalence of TSHrAb is different in in the 2 main form of CAT, i.e. classical Hashimoto's thyroiditis and in atrophic thyroiditis, where TBAb play a major role. Simultaneous presence of both TSAb and TBAb in the serum of the same patient might have clinical implication and cause the shift from hyperthyroidism to hypothyroidism and vice versa. Evaluation of TRAb is recommended in case of patients with Thyroid Associated Orbitopathy not associated with hyperthyroidism. At present, however, the most relevant recommendation for the use of TRAb assay is in patients with CAT secondary to a known agent; in particular, after treatment with alemtuzumab for multiple sclerosis. In conclusion, the routine use of anti-TSH receptor antibodies (either TRAb or TSAb/TBAb) assay cannot be suggested at the present for diagnosis/follow up of patients affected by CAT; there are, however, several conditions where their detection can be clinically relevant.

The Role of Surgery in Autoimmune Conditions of the Thyroid

The two most common autoimmune conditions of the thyroid include chronic lymphocytic (Hashimoto's) thyroiditis and Graves' disease. Both conditions can be treated medically, but surgery plays an important role. Hashimoto's thyroiditis and Graves' disease are mediated by autoantibodies that interact directly with the thyroid, creating inflammation and impacting thyroid function. Patients may develop large goiters with compressive symptoms or malignancy requiring surgical intervention. In addition, there are several surgical indications specific to Hashimoto's and Graves' Disease.

Targeting the thyrotropin receptor in thyroid disease

INTRODUCTION

The thyrotropin receptor (TSHR) is essential for thyroid growth and for the production of thyroid hormones. It is unique among the glycoprotein hormone receptors, in that some of the TSHRs undergo cleavage and shedding of the alpha subunit.

AREAS COVERED

This review discusses the structure and function of the TSHR, followed by an evaluation of its role in thyroid disease. Possible limitations of the TSHR as a therapeutic target are also discussed.

EXPERT OPINION

The TSHR is involved in a number of hereditary and acquired disorders of the thyroid making it of potential importance as a therapeutic target in thyroid disease. Expression of the TSHR in several non-thyroidal tissues and the development of systemic manifestations of thyroid disease suggest that the TSHR is also of interest as a therapeutic target outside the thyroid.

A 5-year-old boy with atrophic autoimmune thyroiditis caused by thyroid-stimulation blocking antibodies

A 5-year-old boy was presented for a growth disturbance, which was initially noted at 3 years of age. Endocrinological testing identified severe hypothyroidism, defined by the following levels: TSH 990.5 microU/mL, F-T3 0.26 pg/mL, and F-T4 0.09 ng/dL. Serum anti-thyroid peroxidase (TPO) antibodies were 158 IU/mL and serum thyroid-stimulation blocking antibodies (TSBab) levels were 82.1 IU/mL (normal range < 45.6). Thyroid scintigraphy with 99mTc showed markedly decreased uptake, and magnetic resonance imaging (MRI) revealed pituitary hyperplasia. He was diagnosed with atrophic autoimmune thyroiditis. His thyroid function and pituitary size normalized following thyroid hormone replacement therapy. We report a rare case of a young boy with atrophic thyroiditis caused by TSBab.

Thyroid volume in hypothyroidism due to autoimmune disease follows a unimodal distribution: evidence against primary thyroid atrophy and autoimmune thyroiditis being distinct diseases

CONTEXT

Primary overt autoimmune hypothyroidism is often divided into primary idiopathic hypothyroidism with thyroid atrophy (Ord's disease) and hypothyroidism with goitre (Hashimoto's disease).

OBJECTIVE

The aim of the present study was to characterize the two subtypes of disease.

DESIGN AND SETTING

This was a population-based study identifying patients newly diagnosed with overt autoimmune hypothyroidism.

PATIENTS

We prospectively identified all patients with incident overt autoimmune hypothyroidism in a Danish population cohort, and 247 patients were invited to join a comprehensive program including thyroid ultrasonography and measurements of thyroid autoantibodies. Of the 144 patients investigated (58% of all invited), 139 were compared with 556 sex-, age-, and region-matched controls from the cohort.

RESULTS

Patients had lower median (11.6 ml vs. 13.5 ml, P = 0.001) and a more dispersed distribution of thyroid volumes compared with controls (P < 0.001). Log thyroid volume showed a Gaussian distribution in both males and females with no bimodal pattern. Nearly all patients had measurable thyroid autoantibodies, but with increasing thyroid volume (quartile I, II, III, and IV), levels of circulating antibodies were higher (median thyroid peroxidase autoantibody 1540, 3122, 4686, and 7058 kU/liter; median thyroglobulin autoantibody 72, 143, 119, and 1195 kU/liter), and thyroid volume correlated negatively with echogenicity (r = -0.21, P = 0.011). Patients with the smallest volumes were biochemically more hypothyroid at diagnosis (median serum T(4) 21.0, 45.5, 45.0, and 36.7 nmol/liter; median serum TSH 81.0, 40.9, 45.4, and 55.6 mU/liter). No difference between groups was observed in prevalence of TSH receptor autoantibody (14.7, 5.6, 14.7, and 8.3%) or duration of symptoms before hypothyroidism was diagnosed.

CONCLUSIONS

In primary autoimmune hypothyroidism, thyroid volume follows a normal distribution. Cases with thyroid atrophy and goiter are only extremes within this distribution and do not represent separate disorders. However, patients with low vs. high thyroid volume differ with respects to several characteristics.

TSH receptor antibodies in subjects with type 1 diabetes mellitus

The research was undertaken to study the prevalence of TSH receptor antibody positivity in patients with type 1 diabetes. A total of 74 subjects with type 1 diabetes were enrolled in this cross-sectional study. Thyroid function test and assessment of thyroid autoimmunity with anti-TPO and TSH receptor antibody were done in all patients. A total of 33 males and 41 females with type 1 diabetes were studied. The prevalence of TSH receptor antibody positivity alone was 18%. The prevalence of thyroid autoimmunity with anti-TPO as a marker was 28%; the prevalence increased to 43% when TSH receptor antibody was also measured. Majority of the subjects with antithyroid antibody positivity were also positive for GAD65 antibodies. As a significant proportion of type 1 diabetic subjects have positivity to TSH receptor antibody, we suggest that larger studies should be conducted to study the benefits of TSH receptor antibody-based screening for thyroid dysfunction in type 1 diabetic subjects. As the TSH receptor antibodies could be of the stimulating or of the blocking type, subjects with antibody positivity could be at risk of developing hyperthyroidism or hypothyroidism.

Graves' ophthalmopathy and atrophic thyroiditis: a case report

Graves' ophthalmopathy (GO)--also known as thyroid-associated orbitopathy or ophthalmopathy--usually affects patients with Graves' disease. Antibodies stimulating the TSH receptor are thought to be involved in the pathogenesis of this important and disabling extra-thyroidal manifestation of Graves' disease. Less frequently, GO occurs in subjects who neither have nor have ever shown evidence of thyroid dysfunction ("euthyroid GO"), while the occurrence of GO in patients with autoimmune Hashimoto's thyroiditis is thought to be quite rare and has sporadically been reported. The late and abrupt occurrence of severe GO without hyperthyroidism in an 88-yr-old woman with primary myxedema due to atrophic thyroiditis must be considered as an exceptional event. In this patient, GO was combined with elevated titres of serum auto-antibodies directed against the TSH receptor, while serum levels of anti-thyroglobulin and thyroperoxidase antibodies were within the normal range or only occasionally slightly above the normal values.

TSH-receptor antibody measurement for differentiation of hyperthyroidism into Graves' disease and multinodular toxic goitre: a comparison of two competitive binding assays

OBJECTIVES

Graves' disease is characterized by stimulating autoantibodies to the TSH-receptor (TRAb). The aim of this study was to compare the performance of a new TRAb assay based on competitive binding to recombinant human TSH-receptors (H-TRAb) with an assay employing purified porcine TSH-receptors (P-TRAb). Furthermore, to evaluate the applicability of the H-TRAb assay to discriminate between patients with hyperthyroidism due to Graves' disease (GD) and multinodular toxic goitre (MNTG).

DESIGN AND MEASUREMENTS

H-TRAb and P-TRAb were measured in patients with newly diagnosed hyperthyroidism due to GD (n = 106) and MNTG (n = 94). For comparison, TRAb was measured in patients with primary autoimmune hypothyroidism, euthyroid subjects with an enlarged thyroid gland by ultrasound, and healthy controls (n = 100 for each group). Patients were consecutively included from a population survey.

RESULTS

If the cut-off values recommended by the manufacturer for TSH-receptor antibody positivity were used for evaluation, the sensitivity of the H-TRAb assay vs. the P-TRAb assay in diagnosing GD was: 95.3/67.9% (P < 0.001). Specificity was (H/P-TRAb): 99/99%. The sensitivity of P-TRAb was increased if the upper 97.5% limit of measurements in controls was used as cut-off (H-TRAb vs. P-TRAb: 95.3/80.2%, P < 0.001). Specificity (H/P-TRAb): 98/98%. The difference between assay performance may partly be due to a better technical performance of the H-TRAb assay with more reliable results in the low range of measurements. However, even in GD patients with clearly measurable TRAb, 25% had a P-TRAb < 50% of the value expected from the H-TRAb measurement. This suggests that a subgroup of patients produce TRAb with a higher affinity for the human than the porcine TSH receptor. A relatively high proportion of patients with MNTG were TRAb positive (H-TRAb/P-TRAb: 17/9%). Characteristics of H-TRAb positive and negative MNTG patients were compared. There was no difference between size of thyroid gland and number of nodules by ultrasonography. H-TRAb positive patients had significantly higher serum T4 and T3 and a greater number were TPO-Ab positive.

CONCLUSIONS

H-TRAb diagnosed Graves' disease with a high sensitivity and specificity than P-TRAb. The high occurrence of TRAb in multinodular toxic goitre might in part reflect an overlap between Graves' disease and multinodular toxic goitre in some patients.

Thyroid autoantibodies

Although assays to detect thyroid autoantibodies have been available for more than 40 years, their place in the clinical management of thyroid disease has remained controversial; however, novel automated detection techniques using recombinant antigens are increasing the sensitivity and specificity of the assays, particularly for antibodies to the TSH receptor. In addition, new antigenic targets have been defined including the sodium-iodide symporter and four eye muscle proteins targeted in Graves' ophthalmopathy. This article summarizes the immunobiology, assay methodology and prevalence in thyroid diseases of each of the major thyroid autoantibodies before discussing the clinical indications for their use in thyroid diseases.

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.

Differences in the levels of TSH-binding inhibitor immunoglobulins in goitrous and agoitrous autoimmune thyroiditis after twelve months of L-thyroxine therapy

OBJECTIVE

The aims were to study the prevalence of TSH binding inhibitor immunoglobulins (TBII) in newly diagnosed patients with autoimmune hypo-thyroidism, to determine if clinical and biochemical parameters in these patients differed, and to study the course of these antibodies after 12 months of L-thyroxine (LT4) therapy.

SUBJECTS AND DESIGN

In a prospective study, 111 consecutive patients with newly diagnosed auto-immune hypothyroidism were enrolled. Patients were divided into groups according to the presence or absence of a goitre and TBII levels. Clinical and biochemical differences in these patients were analysed. Patients were then treated with L-thyroxine (LT4) for 12 months and changes in their TBII monitored.

MEASUREMENTS

Free T4 and TSH levels were measured at baseline and then 6-weekly during the titration of LT4 doses. Once TSH levels had normalized, these measurements were performed 3 monthly. TBII levels were measured in patients at baseline and 12 months. Thyroid stimulating blocking antibody (TSBAb) levels were measured 12-18 months after initiation of LT4 therapy.

RESULTS

Twenty patients were TBII-positive, 10 goitrous and 10 agoitrous. Agoitrous TBII-positive patients were found to have similar characteristics: these included TBII levels > 100 U/l, potent thyroid stimulating blocking antibody (TSBAb) activity and a tendency for TBII levels to remain unchanged or to rise after LT4 therapy. The degree of hypothyroidism seen in these cases was significantly greater than in all other groups. In contrast, goitrous TBII-positive patients were heterogenous, most did not have significant TSBAb activity and TBII disappeared in 5 out of 10 cases after a year of LT4 treatment. While TBII disappeared in 6 of the 20 patients after a year, remission of hypothyroidism occurred in only 3 cases.

CONCLUSIONS

The degree of hypothyroidism in agoitrous TSH-binding inhibitor immunoglobulins-positive patients appears to be more severe than that seen in other forms of AIT. The differences in thyroid stimulating blocking antiboby activity and response to LT4 therapy in agoitrous and goitrous autoimmune thyroiditis suggest that the TSH-binding inhibitor immunoglobulins in these patients are fundamentally different. The disappearance of TSH-binding inhibitor immunoglobulins in hypothyroid patients was not accompanied by the reversal of hypothyroidism in 50% of patients.

Two Graves' disease patients who spontaneously developed hypothyroidism after antithyroid drug treatment: characteristics of epitopes for thyrotropin receptor antibodies

Few reports have identified blocking thyrotropin receptor antibodies (TSHRAbs) as a pathogenic mechanism explaining spontaneous hypothyroidism after antithyroid drug (ATD) treatment of Graves' disease. Here we report 2 Graves' patients who showed different courses of hypothyroidism after ATD treatment. The first patient had Graves' hyperthyroidism and was treated with ATD for 1 year. After a short period of euthyroidism, she developed permanent hypothyroidism with blocking TSHRAb. The second patient became euthyroid after 1 year of ATD treatment. After 3 years, however, she presented with hypothyroidism with blocking TSHRAb activity. Her hypothyroidism was transient, and restoration of euthyroidism was followed by disappearance of blocking TSHRAb. Blocking and stimulating TSHRAbs activities of these 2 patients were serially measured using Chinese hamster ovary (CHO) cells transfected with wild-type human TSHR (CHO-hTSHR) and 2 TSHR chimeras with residues 8-165 (Mc1+2) or 90-165 (Mc2) substituted by equivalent residues of the luteinizing hormone/chorionic gonadotropin receptor (LH/CGR). During their hypothyroid phases, blocking TSHRAbs activities were positive in all 3 kinds of assays and stimulating TSHRAbs activities were negative in CHO-hTSHR or in Mc 1+2 assay. Mc2 stimulating TSHRAb activity was detected in sera of hypothyroid phase of the second patient who had transient hypothyroidism but not in the first whose hypothyroidism was permanent. In these 2 cases, we demonstrate the causative role of blocking TSHRAb in the development of hypothyroidism after ATD treatment in Graves' patients. Interestingly, the difference in the course of blocking TSHRAb-induced hypothyroidism was associated with the difference in epitope reactivities of TRAb during hypothyroid phase that developed after ATD treatment of Graves' disease.