Dissociation of responsiveness to thyrotropin-releasing hormone and thyroid suppressibility following antithyroid drug therapy of hyperthyroidism

Current perspective on the pathogenesis of Graves' disease and ophthalmopathy

Graves' disease (GD) is a very common autoimmune disorder of the thyroid in which stimulatory antibodies bind to the thyrotropin receptor and activate glandular function, resulting in hyperthyroidism. In addition, some patients with GD develop localized manifestations including ophthalmopathy (GO) and dermopathy. Since the cloning of the receptor cDNA, significant progress has been made in understanding the structure-function relationship of the receptor, which has been discussed in a number of earlier reviews. In this paper, we have focused our discussion on studies related to the molecular mechanisms of the disease pathogenesis and the development of animal models for GD. It has become apparent that multiple factors contribute to the etiology of GD, including host genetic as well as environmental factors. Studies in experimental animals indicate that GD is a slowly progressing disease that involves activation and recruitment of thyrotropin receptor-specific T and B cells. This activation eventually results in the production of stimulatory antibodies that can cause hyperthyroidism. Similarly, significant new insights have been gained in our understanding of GO that occurs in a subset of patients with GD. As in GD, both environmental and genetic factors play important roles in the development of GO. Although a number of putative ocular autoantigens have been identified, their role in the pathogenesis of GO awaits confirmation. Extensive analyses of orbital tissues obtained from patients with GO have provided a clearer understanding of the roles of T and B cells, cytokines and chemokines, and various ocular tissues including ocular muscles and fibroblasts. Equally impressive is the progress made in understanding why connective tissues of the orbit and the skin in GO are singled out for activation and undergo extensive remodeling. Results to date indicate that fibroblasts can act as sentinel cells and initiate lymphocyte recruitment and tissue remodeling. Moreover, these fibroblasts can be readily activated by Ig in the sera of patients with GD, suggesting a central role for them in the pathogenesis. Collectively, recent studies have led to a better understanding of the pathogenesis of GD and GO and have opened up potential new avenues for developing novel treatments for GD and GO.

Epitope heterogeneity of thyroid-stimulating antibodies predicts long-term outcome in Graves' patients treated with antithyroid drugs

Differences in the epitopes of thyroid-stimulating antibodies (TSAbs) from patients with untreated Graves' disease were compared with long-term response to antithyroid drugs. Epitopes were measured using Chinese hamster ovary cells transfected with wild-type human TSH receptor (TSHR) and two receptor chimeras, wherein TSHR residues 9-165 or 90-165 had been substituted with comparable residues of the LH/chorionic gonadotropin receptor. Of 159 patients studied, 52 (32.7%) exhibited positive TSAb activity with one or both chimera lines (heterogeneous group), and 107 (67.3%) had no activity with either (homogeneous group). Independent of all other parameters, patients with heterogeneous epitopes responded more favorably to oral antithyroid drugs than patients with homogeneous epitopes (65.4% vs. 41.9%, P = 0.011: estimated odds ratio by logistic regression, 2.17). Although most clinical parameters were not different at presentation, significant differences in the size of goiters, total T(3) concentrations, and titers of TSH-binding inhibitory Igs were evident in the successfully treated group (n = 80) by comparison to the group of patients whose treatment failed (n = 79). Alone, these three parameters did not predict outcome; however, when either of these parameters were considered together with epitope heterogeneity, predictability of a positive therapeutic response was increased to nearly 80%. Thus, the presence of TSAbs with a heterogeneous epitope in a patient with Graves' disease is not only associated with a favorable response to antithyroid drug treatment, it may help predict the response to treatment when the patient is initially seen.

Age and gender predict the outcome of treatment for Graves' hyperthyroidism

The response to treatment in Graves' hyperthyroidism is unpredictable, and factors postulated to predict outcome have not generally proved clinically useful or been widely adopted in clinical practice. We audited outcome in 536 patients with Graves' hyperthyroidism presenting consecutively to determine whether simple clinical features predict disease presentation and response to treatment. At presentation males had slightly more severe biochemical hyperthyroidism [free T4: males, 64.3 +/- 3.0 pmol/L (mean +/- SE); females, 61.3 +/- 1.7 (P = 0.45); free T3: males, 24.3 +/- 1.5 pmol/L; females, 21.0 +/- 0.6, (P = 0.04)]. Patients less than 40 yr at diagnosis had more severe hyperthyroidism than patients more than 40 yr old [free T4: <40 yr, 64.3 +/- 2.0; >40 yr, 56.7 +/- 2.3 (P = 0.02); free T3: <40 yr, 22.8 +/- 0.8; >40 yr, 19.0 +/- 0.9 (P = 0.003)]. Males had a lower remission rate than females after a course of antithyroid medication [19.6% vs. 40%; odds ratio, 0.37; 95% confidence interval (CI), 0.17-0.79; P < 0.01]. Similarly, patients aged less than 40 yr had a lower remission rate than older patients (32.6% vs. 47.8%; odds ratio, 0.53; 95% CI, 0.32-0.87; P = 0.01). One dose of radioiodine cured hyperthyroidism in fewer males than females (47% vs. 74%; P < 0.0001). Logistic regression analysis demonstrated male sex (odds ratio, 2.80; 95% CI, 1.31-5.98; P = 0.008), serum free T4 concentration at diagnosis (odds ratio, 1.02; 95% CI, 1.0-1.04; P = 0.01), and dose of radioiodine administered (odds ratio, 0.99; 95% CI, 0.99-1.00; P = 0.001) were contributing factors associated with failure to respond to a single dose of radioiodine. As males and younger patients are more likely to fail to respond to medical treatment, and male patients are likewise less likely to respond to a single dose of radioiodine, we suggest that those groups with low remission rates should be offered definitive treatment with radioiodine or surgery soon after presentation and that the value of higher initial doses of radioiodine in males be evaluated.

Clinical features of patients with Graves' disease undergoing remission after antithyroid drug treatment

The clinical course of 306 Graves' patients treated with methimazole (MMI) was reviewed with the aim of establishing criteria able to predict remission of hyperthyroidism after medical treatment. One hundred and ninety-four (149 females, 45 males) of 306 (63.4%) patients had relapse of hyperthyroidism after antithyroid drug (ATD) withdrawal. Relapse was more frequent during the first months of the follow-up, but still it was observed 3 years after MMI withdrawal. The relapse rate was dependent on the age of the patient, the size of goiter, and the level of TSH-receptor antibody (TRAb) at diagnosis, being observed in 40 of 47 (85%) patients with high (> 30 U/L) TRAb level and in 54 of 101 (53%) patients with low TRAb level (< or = 30 U/L; p <.0002). Remission was more frequent (43.3%) in patients having the combination goiter size < or = 40 mL, TRAb level < or = 30 U/L, than in patients with goiter size > 40 mL and high TRAb levels (9%). In the subgroup of patients with the combination: goiter < or = 40 mL- TRAb < or = 30 U/L - age at onset > 40 years, the remission rate was 80%, and all relapses occurred within the first 9 months after MMI withdrawal. In conclusion, our study confirms that hyperthyroidism relapses in the majority of patients with Graves' disease treated with ATD. Among different clinical and laboratory features, age at onset of hyperthyroidism, goiter size and TRAb level are particularly helpful in identifying those patients who are more prone to undergo a remission of hyperthyroidism after medical treatment and may be useful to select the minority of Graves' patients who will benefit from antithyroid drug treatment as a first choice.

The pathogenesis of Graves' disease

The abnormally increased thyroid activity that is characteristic of Graves' disease is caused by immunoglobulins which specifically interact with the thyroid cell and stimulate it. Increases and decreases in thyroid activity in Graves' disease can be clearly related to rise and fall of these immunoglobulin-mediated activities. The level of immunoglobulin stimulatory activity can be used for prediction of the likelihood of neonatal Graves' disease and of recurrence of disease after cessation of treatment with antithyroid drugs. Investigation of patients with Graves' disease and their families has led to identification of particular human leukocyte antigens and genetically linked markers on immunoglobulins which both appear to incur increased susceptibility to certain autoimmune diseases. Differences in immune function, when compared with control populations, have been found in patients with these genetically linked markers. Protection against autoimmune disease is maintained by purposeful inhibition of any self-directed activity within each function of the immune system and by the controlling interaction of other immune functions. No single deficiency of immune function can be selected as giving the major risk of autoimmune disease, but rather a sum of relative defects resulting in an increased risk. In some patients with Graves' disease the self-protection mechanisms regain sufficient control of the immune functions to reduce the activity of the autoimmune disease, and the patient may achieve clinical remission. Often, however, there is evidence that abnormal immune activity directed against thyroid tissue has persisted with liability to recurrence of the Graves' disease.

Antithyroid drugs

Over the past four decades, a great deal has been learned about the pharmacology and mechanisms of action of antithyroid drugs. Their ability to inhibit hormone biosynthesis involves complex interactions with thyroid peroxidase and thyroglobulin, many of which are still poorly understood. Their spectrum of activity is much wider than previously thought, and a number of clinically important extrathyroidal actions have been identified. Despite a greater appreciation for the intricacies of antithyroid-drug pharmacology, controversies still surround the use of these agents in the treatment of thyrotoxicosis. These controversies are apt to continue until the pathophysiology of Graves' disease is fully elucidated.

Spontaneous hypothyroidism after antithyroid treatment of hyperthyroid Graves' disease

Out of 54 patients with hyperthyroid Graves' disease 35 remained euthyroid after treatment with antithyroid agents and have been continuously followed from 1 to 9 yr (4.85 +/- 2.55 yr, mean +/- SD). In 4 patients an exaggerated TSH response to TRH developed from 30 to 111 months after interrupting the treatment and one of them became hypothyroid 50 months (5.0 yr) thereafter. The annual incidence of subclinical hypothyroidism (exaggerated response to TRH) as calculated from the total number of observation yr was 2.5% and that of overt hypothyroidism was 0.6%. These figures are similar to those reported recently in 2 retrospective studies.

Clinical application of a cytochemical bioassay for the determination of thyroid stimulating hormone

Thyroid stimulating hormone (TSH) was measured using a highly sensitive cytochemical bioassay (CBA) technique in normal subjects, in patients with Graves' disease (untreated and treated) and in patients with euthyroid goiter and negative thyrotropin-releasing hormone (TRH)-test. Plasma TSH levels of normal subjects and of subjects with untreated Graves' disease were reduced after the plasma had been incubated with a specific antibody to human TSH, indicating that the thyroid stimulating substance measured with this assay was likely to be TSH. Basal TSH levels in patients with Graves' disease and in a special group of patients with euthyroid goiter and negative TRH test were low but detectable. They did not rise after TRH administration. Increased TSH release (4.5- to 10-fold) after TRH stimulation was demonstrated, however, in two formerly hyperthyroid patients after treatment. This increase was not detected by radioimmunoassay (RIA) due to limited sensitivity.

Response to thyrotrophin-releasing hormone and triiodothyronine suppressibility in euthyroid multinodular goitre

In twenty-two female patients with euthyroid multinodular goitre of varying size, thyroid suppression of 131I thyroid uptake by triiodothyronine (T3) and thyrotrophin (TSH) release after thyrotrophin-releasing hormone (TRH) administration were compared with thyroid weight, estimated by a planimetric method, and with serum thyroxine (T4) and T3 concentrations. Maximal increment of TSH (deltaTSH) after TRH and per cent T3-suppressibility were inversely related to thyroid weight and not related to basal serum T4 or T3 concentrations. deltaTSH and per cent suppression correlated positively, but deltaTSH was more often subnormal than T3-suppressibility. A practical consequence of our study is that nonconformity of the two tests may occur. This should be kept in mind in the evaluation of patients with thyroid disorders.