Sources of circulating 3,5,3'-triiodothyronine in hyperthyroidism estimated after blocking of type 1 and type 2 iodothyronine deiodinases

The value of FT4/TSH ratio in the differential diagnosis of Graves' disease and subacute thyroiditis

Objective

To explore the value of the FT4/TSH ratio in the etiological diagnosis of newly diagnosed patients with thyrotoxicosis.

Methods

The retrospective study was conducted on 287 patients with thyrotoxicosis (122 patients with subacute thyroiditis and 165 patients with Graves' disease) and 415 healthy people on their first visit to our hospital. All patients underwent thyroid function tests including the measurement of T3, T4, FT3, FT4, TSH, T3/TSH, and T4/TSH. The receiver operating characteristic (ROC) curve was employed to evaluate the value of FT4/TSH in the differential diagnosis of Graves' disease and subacute thyroiditis, and compared with other related indicators.

Results

The area under the curve of FT4/TSH for diagnosing Graves' disease and thyroiditis was 0.846, which was significantly larger than the area under the curve of T3/T4 ratio (P< 0.05) and FT3/FT4 ratio (P< 0.05). When the cut-off value of the FT4/TSH ratio was 5731.286 pmol/mIU, the sensitivity was 71.52%, the specificity was 90.16%, the positive predictive value was 90.77% and the negative predictive value was 70.06%. The diagnostic accuracy was 79.44%.

Conclusion

FT4/TSH ratio can be used as a new reference index for the differential diagnosis of thyrotoxicosis.

Gestational thyroid hormone concentrations and risk of attention-deficit hyperactivity disorder in the Norwegian Mother, Father and Child Cohort Study

BACKGROUND

Maternal thyroid function plays an important role in foetal brain development; however, little consensus exists regarding the relationship between normal variability in thyroid hormones and common neurodevelopmental disorders, such as attention-deficit hyperactivity disorder (ADHD).

OBJECTIVE

We sought to examine the association between mid-pregnancy maternal thyroid function and risk of clinically diagnosed ADHD in offspring.

METHODS

We conducted a nested case-control study in the Norwegian Mother, Father and Child Cohort Study. Among children born 2003 or later, we randomly sampled singleton ADHD cases obtained through linkage with the Norwegian Patient Registry (n = 298) and 554 controls. Concentrations of maternal triiodothyronine (T3), thyroxine (T4), T3-Uptake, thyroid-stimulating hormone (TSH) and thyroid peroxidase antibody (TPO-Ab) were measured in maternal plasma, collected at approximately 17 weeks' gestation. Indices of free T4 (FT4i) and free T3 (FT3i) were calculated. We used multivariable adjusted logistic regression to calculate odds ratios and accounted for missing covariate data using multiple imputation. We used restricted cubic splines to assess non-linear trends and provide flexible representations. We examined effect measure modification by dietary iodine and selenium intake. In sensitivity analyses, we excluded women with clinically significant thyroid disorders (n = 73).

RESULTS

High maternal T3 was associated with increased risk of ADHD (5th vs 1st quintile odds ratio  2.27, 95% confidence interval 1.21, 4.26). For FT4i, both the lowest and highest quintiles were associated with an approximate 1.6-fold increase in risk of ADHD, with similar trends found for T4. The FT4i association was modified by dietary iodine intake such that the highest risk strata were confined to the low intake group.

CONCLUSIONS

Both high and low concentrations of maternal thyroid hormones, although within population reference ranges, increase the risk of ADHD in offspring. Increased susceptibility may be found among women with low dietary intake of iodine and selenium.

Treatment of Graves' Disease Associated With Severe Neutropenia

Severe neutropenia in newly diagnosed hyperthyroidism is a diagnostic and therapeutic dilemma since antithyroid drugs (ATDs) cannot be started if the absolute neutrophil count (ANC) is <1 x 10⁹/L. We report the case of a patient followed for hyperthyroidism associated with severe neutropenia treated with dexamethasone and ATD. The patient was 51 years old and was hospitalized for hyperthyroidism with a thyroid stimulating hormone (TSH) level <0.005 (0.4-4) mUI/L, T4 at 415 (9.3-17.1) ng/L and T3 at 148 (2-4.4) pg/mL on Graves' disease (GD) confirmed by the TSH receptor antibodies at 38 IU/mL and scintigraphy, associated with neutropenia, with ANC at 0.4 x 10⁹/L. He was put on prednisolone 60 mg/day and propranolol 60 mg/day for three weeks without improvement. Faced with the association of hyperthyroidism and severe neutropenia, we could not start the ATD for fear of agranulocytosis; we put the patient on propranolol 60 mg and dexamethasone 6 mg with progressive degression resulting in a spectacular increase of ANC from 0.4 x 10⁹/L to 7.1 x 10⁹/L, which allowed us to start the ATD (carbimazole) at a dose of 30 mg, and then 50 mg, with monitoring of ANC and transaminases every 48 hours. Euthyroidism was achieved after 15 days. A curative treatment with radioactive iodine ablation was administered. Our patient did not respond to prednisolone but responded dramatically to dexamethasone; this leads us to consider using dexamethasone for the rapid preparation for radical treatment of patients with GD.

The polymorphic inheritance of DIO2 rs225014 may predict body weight variation after Graves' disease treatment

OBJECTIVE

We aimed to investigate the role of DIO2 polymorphisms rs225014 and rs12885300 in Graves' disease patients, mainly for controlling body weight following treatment.

METHODS

We genotyped 280 GD patients by the time of diagnosis and 297 healthy control individuals using a TaqMan SNP Genotyping technique. We followed up 141 patients for 18.94 ± 6.59 months after treatment.

RESULTS

There was no relationship between the investigated polymorphisms with susceptibility to GD and gain or loss of weight after GD treatment. However, the polymorphic inheritance (CC+CT genotype) of DIO2 rs225014 was associated with a lower body weight variation after GD treatment (4.26 ± 6.25 kg) when compared to wild type TT genotype (6.34 ± 7.26 kg; p = 0.0456 adjusted for the follow-up time). This data was confirmed by a multivariate analysis (p = 0.0138) along with a longer follow-up period (p = 0.0228), older age (p = 0.0306), treatment with radioiodine (p-value = 0.0080) and polymorphic inheritance of DIO2 rs12885300 (p = 0.0306).

CONCLUSION

We suggest that DIO2 rs225014 genotyping may have an auxiliary role in predicting the post-treatment weight behavior of GD patients.

Pregnancy exposure to common-detect organophosphate esters and phthalates and maternal thyroid function

BACKGROUND

Contemporary human populations are exposed to elevated concentrations of organophosphate esters (OPEs) and phthalates. Some metabolites have been linked with altered thyroid function, however, inconsistencies exist across thyroid function biomarkers. Research on OPEs is sparse, particularly during pregnancy, when maintaining normal thyroid function is critical to maternal and fetal health. In this paper, we aimed to characterize relationships between OPEs and phthalates exposure and maternal thyroid function during pregnancy, using a cross-sectional investigation of pregnant women nested within the Norwegian Mother, Father, and Child Cohort (MoBa).

METHODS

We included 473 pregnant women, who were euthyroid and provided bio-samples at 17 weeks' gestation (2004-2008). Four OPE and six phthalate metabolites were measured from urine; six thyroid function biomarkers were estimated from blood. Relationships between thyroid function biomarkers and log-transformed concentrations of OPE and phthalate metabolites were characterized using two approaches that both accounted for confounding by co-exposures: co-pollutant adjusted general linear model (GLM) and Bayesian Kernal Machine Regression (BKMR).

RESULTS

We restricted our analysis to common-detect OPE and phthalate metabolites (>94%): diphenyl phosphate (DPHP), di-n-butyl phosphate (DNBP), and all phthalate metabolites. In GLM, pregnant women with summed di-isononyl phthalate metabolites (∑DiNP) concentrations in the 75th percentile had a 0.37 ng/μg lower total triiodothyronine (TT3): total thyroxine (TT4) ratio (95% credible interval: [-0.59, -0.15]) as compared to those in the 25th percentile, possibly due to small but diverging influences on TT3 (-1.99 ng/dL [-4.52, 0.53]) and TT4 (0.13 μg/dL [-0.01, 0.26]). Similar trends were observed for DNBP and inverse associations were observed for DPHP, monoethyl phthalate, mono-isobutyl phthalate, and mono-n-butyl phthalate. Most associations observed in co-pollutants adjusted GLMs were attenuated towards the null in BKMR, except for the case of ∑DiNP and TT3:TT4 ratio (-0.48 [-0.96, 0.003]).

CONCLUSIONS

Maternal thyroid function varied modestly with ∑DiNP, whereas results for DPHP varied by the type of statistical models.

Severe Hypothyroxinemia in a Young Adult with Carbimazole-Treated T3-Predominant Graves' Hyperthyroidism, Reversed with L-Thyroxine Loading Immediately Post-Total Thyroidectomy

Patients with triiodothyronine (T3)-predominant Graves’ hyperthyroidism with markedly elevated serum thyroid stimulating immunoglobulin (TSI) levels and massive goitre may display discordant hypothyroxinemia with eutriiodothyroninemia or hypertriiodothyroninemia while on anti-thyroid drug therapy. A 25-year-old female with the above was started on oral carbimazole therapy for 9 months before total thyroidectomy. Preoperatively, her serum free T4 was reduced to below detection limit, and total T4 reduced to 11% of lower limit of normal, while T3 levels remained normal, and TSH remained largely suppressed. Immediately after total-thyroidectomy, a loading dose of L-thyroxine (L-T4) was administered intravenously. She was extubated without any postoperative complications. Serum free and total T4, and TSH normalized within the next 24 hours. The peculiar thyroid axis dynamics and use of L-T4 postoperative loading in such a rare clinical scenario are discussed.

Thyroid disorders in elderly: A comprehensive review

The approach to management of thyroid disorders in the elderly differs from that for younger individuals: it considers frailty of the population, coexisting medical illness and medications, clearance rate of medications and drug-drug interactions along with target organ sensitivity to the treatment. We present a comprehensive review of literature for the clinical presentation, pathophysiology, diagnostic evaluation, and management of thyroid disorders in the elderly.

Agoitrous Graves' Hyperthyroidism with Markedly Elevated Thyroid Stimulating Immunoglobulin Titre displaying Rapid Response to Carbimazole with Discordant Thyroid Function

We characterize the clinical and laboratory characteristics of 5 patients with Graves’ thyrotoxicosis whose serum free thyroxine (fT4) concentration decreased unexpectedly to low levels on conventional doses of carbimazole (CMZ) therapy. The initial fT4 mean was 40.0 pM, range 25–69 pM. Thyroid volume by ultrasound measured as mean 11 ml, range 9.0–15.6 ml. Initial TSI levels measured 1487% to >4444%. Serum fT4 fell to low-normal or hypothyroid levels within 3.6 to 9.3 weeks of initiating CMZ 5 to 15 mg daily, and subsequently modulated by fine dosage adjustments. In one patient, serum fT4 fluctuated in a “yo-yo” pattern. There also emerged a pattern of low normal/low serum fT4 levels associated with discordant low/mid normal serum TSH levels respectively, at normal serum fT3 levels. The long-term daily-averaged CMZ maintenance dose ranged from 0.7 mg to 3.2 mg. Patients with newly diagnosed Graves’ hyperthyroidism who have small thyroid glands and markedly elevated TSI titres appear to be “ATD dose sensitive.” Their TFT on ATD therapy may display a “central hypothyroid” pattern. We suggest finer CMZ dose titration at closer follow-up intervals to achieve biochemical euthyroidism.

Liothyronine and Desiccated Thyroid Extract in the Treatment of Hypothyroidism

Background: The basis for the treatment of hypothyroidism with levothyroxine (LT4) is that humans activate T4 to triiodothyronine (T3). Thus, while normalizing serum thyrotropin (TSH), LT4 doses should also restore the body's reservoir of T3. However, there is evidence that T3 is not fully restored in LT4-treated patients. Summary: For patients who remain symptomatic on LT4 therapy, clinical guidelines recommend, on a trial basis, therapy with LT4+LT3. Reducing the LT4 dose by 25 mcg/day and adding 2.5-7.5 mcg liothyronine (LT3) once or twice a day is an appropriate starting point. Transient episodes of hypertriiodothyroninemia with these doses of LT4 and LT3 are unlikely to go above the reference range and have not been associated with adverse drug reactions. Trials following almost a 1000 patients for almost 1 year indicate that similar to LT4, therapy with LT4+LT3 can restore euthyroidism while maintaining a normal serum TSH. An observational study of 400 patients with a mean follow-up of ∼9 years did not indicate increased mortality or morbidity risk due to cardiovascular disease, atrial fibrillation, or fractures after adjusting for age when compared with patients taking only LT4. Desiccated thyroid extract (DTE) is a form of combination therapy in which the LT4/LT3 ratio is ∼4:1; the mean daily dose of DTE needed to normalize serum TSH contains ∼11 mcg T3, but some patients may require higher doses. The DTE remains outside formal FDA oversight, and consistency of T4 and T3 contents is monitored by the manufacturers only. Conclusions: Newly diagnosed hypothyroid patients should be treated with LT4. A trial of combination therapy with LT4+LT3 can be considered for those patients who have unambiguously not benefited from LT4.

Eosinophil/Monocyte Ratio Combined With Serum Thyroid Hormone for Distinguishing Graves' Disease and Subacute Thyroiditis

Background: Thyrotoxicosis is commonly classified into several entities according to different etiologies. Identifying the causes of thyroid dysfunction is critical for the subsequent selection of treatment. The free triiodothyronine to free thyroxine ratio (fT₃/fT₄) is widely used but is still a controversial diagnostic measurement. Methods: A total of 290 patients including 141 healthy control subjects, 86 patients with untreated Graves' disease (GD,) and 63 patients with subacute thyroiditis (SAT) were enrolled in the study. The main aim was to evaluate the diagnostic value of different indexes from serum testing including fT₃, fT₄, eosinophils (Eo) and monocytes (Mo). The diagnostic performance of multiple indexes was evaluated separately using receiver operating characteristic curve analysis. Results: Sensitivities and specificities of fT₄/fT₃, Mo/Eo ratios and Mo/Eo ratio + fT₄/fT₃ for diagnosing GD were 80.23 and 88.89, 82.56 and 60.32, and 74.4 and 87.3 with cut-off values of ≤ 2.841, ≤ 8.813 and >0.644, respectively. An equation of combined indicators including Mo, Eo, fT₃, and fT₄ data was developed to calculate a probability value and among all indexes studied the indicator combination formula gave the best diagnostic value, reaching sensitivity and specificity of 89.53 and 90.48%, respectively, with an optimum cut-off value at 0.561 for GD diagnosis. Conclusion: Compared to regular indexes (fT_4/fT₃ and Mo/Eo), a newly developed indicator combination formula provided a higher prediction probability and may serve as a simple, cost-effective tool for differentiating GD from SAT patients, especially in undeveloped regions of China.

Serum Ratio of Free Triiodothyronine to Thyroid-Stimulating Hormone: A Novel Index for Distinguishing Graves' Disease From Autoimmune Thyroiditis

OBJECTIVE

Graves' disease (GD) and autoimmune thyroiditis (AIT) are two major causes of thyrotoxicosis that require correct diagnosis to plan appropriate treatment. The objectives of this study were to evaluate the usefulness of thyroid-related parameters for distinguishing GD from AIT and identify a novel index for differential diagnosis of thyrotoxicosis.

DESIGN

This retrospective study was performed using electronic medical records in Peking University People's Hospital (Beijing, China).

METHODS

In total, 650 patients with GD and 155 patients with AIT from December 2015 to October 2019 were included in cohort 1. Furthermore, 133 patients with GD and 14 patients with AIT from December 2019 to August 2020 were included in cohort 2 for validation of the novel index identified in cohort 1. All patients were of Chinese ethnicity and were newly diagnosed with either GD or AIT. Thyroid-related clinical information was collected before intervention by reviewing the patients' electronic medical records. Receiver operating characteristic curve analysis was used to identify the optimal cutoff for distinguishing GD from AIT.

RESULTS

In cohort 1, thyroid-stimulating hormone (TSH) receptor antibody was identified as the best indicator for distinguishing GD from AIT. The area under the receiver operating characteristic curve was 0.99(95% confidence interval: 0.98-0.99, p<0.0001)and the optimal cutoff was 0.84 IU/l (98% sensitivity and 99% specificity). The free triiodothyronine (FT3)/TSH ratio (FT3/TSH) was the second -best for distinguishing GD from AIT, the area under the receiver operating characteristic curve of FT3/TSH was 0.86 (95% confidence interval: 0.84-0.88, p<0.0001); its optimal cutoff was 1.99 pmol/mIU (79% sensitivity and 80% specificity). Its effectiveness was confirmed in cohort 2 (81% sensitivity and 100% specificity).

CONCLUSIONS

The FT3/TSH ratio is a new useful index for differential diagnosis of thyrotoxicosis, especially when combined with TRAb.

When should antithyroid drug therapy to reduce the relapse rate of hyperthyroidism in Graves' disease be discontinued?

OBJECTIVE

The use of antithyroid drug (ATD) therapy in patients with Graves' disease (GD) hyperthyroidism has been increasing, but ATD therapy is associated with a higher relapse rate. We aimed to evaluate clinical factors for predicting relapse of GD after ATD therapy.

METHODS

Patients (n = 149) with newly diagnosed GD who achieved remission of hyperthyroidism after ATD therapy (≥6 months) were followed up for >18 months after ATD withdrawal. We evaluated the predictive factors of relapse during a median of 6.9 years of follow-up.

RESULTS

Disease relapse occurred in 52 patients (34.9%). By multivariate analyses, a duration of the minimum maintenance dose therapy (MMDT) of <6 months was a significant factor in disease relapse (hazard ratio [HR], 2.58; 95% confidence interval [CI], 1.47-4.52; p < 0.001), and a T3/free T4 (fT4) ratio > 120 at ATD withdrawal was significantly more frequent in patients with relapse (HR 2.43; 95% CI, 1.36-4.34; p = 0.002). In the prediction-of-relapse model, the likelihood of relapse was greater in the high-risk group, which had a short MMDT duration and a T3/fT4 ratio ≥120 (HR, 5.81; 95% CI, 2.52-13.39; p < 0.001) and the intermediate-risk group, which had a short MMDT duration or a T3/fT4 ratio < 120 (HR, 2.77; 95% CI, 1.26-6.13; p < 0.001), than in the low-risk group, which had a long MMDT duration and a T3/fT4 ratio < 120.

CONCLUSION

An MMDT longer than 6 months and a high T3/fT4 ratio at ATD withdrawal were independent predictors of relapse in patients who achieved initial remission after ATD for GD. These factors could be used to determine the optimal time to withdraw ATD during the treatment of GD hyperthyroidism.

Paradigms of Dynamic Control of Thyroid Hormone Signaling

Thyroid hormone (TH) molecules enter cells via membrane transporters and, depending on the cell type, can be activated (i.e., T4 to T3 conversion) or inactivated (i.e., T3 to 3,3'-diiodo-l-thyronine or T4 to reverse T3 conversion). These reactions are catalyzed by the deiodinases. The biologically active hormone, T3, eventually binds to intracellular TH receptors (TRs), TRα and TRβ, and initiate TH signaling, that is, regulation of target genes and other metabolic pathways. At least three families of transmembrane transporters, MCT, OATP, and LAT, facilitate the entry of TH into cells, which follow the gradient of free hormone between the extracellular fluid and the cytoplasm. Inactivation or marked downregulation of TH transporters can dampen TH signaling. At the same time, dynamic modifications in the expression or activity of TRs and transcriptional coregulators can affect positively or negatively the intensity of TH signaling. However, the deiodinases are the element that provides greatest amplitude in dynamic control of TH signaling. Cells that express the activating deiodinase DIO2 can rapidly enhance TH signaling due to intracellular buildup of T3. In contrast, TH signaling is dampened in cells that express the inactivating deiodinase DIO3. This explains how THs can regulate pathways in development, metabolism, and growth, despite rather stable levels in the circulation. As a consequence, TH signaling is unique for each cell (tissue or organ), depending on circulating TH levels and on the exclusive blend of transporters, deiodinases, and TRs present in each cell. In this review we explore the key mechanisms underlying customization of TH signaling during development, in health and in disease states.

Type 1 and type 2 iodothyronine deiodinases in the thyroid gland of patients with huge goitrous Hashimoto's thyroiditis

PURPOSE

The serum free triiodothyronine (FT3)/free thyroxine (FT4) ratio in patients with huge goitrous Hashimoto's thyroiditis (HG-HT) is relatively high. We investigated the cause of high FT3/FT4 ratios.

METHODS

We measured the serum FT3, FT4, and thyrotropin (TSH) levels of seven patients with HG-HT who had undergone a total thyroidectomy. Eleven patients with papillary thyroid carcinoma served as controls. The activities and mRNA levels of type 1 and type 2 iodothyronine deiodinases (D1 and D2, respectively) were measured in the thyroid tissues of HG-HT and perinodular thyroid tissues of papillary thyroid carcinoma.

RESULTS

The TSH levels in the HG-HT group were not significantly different from those of the controls. The FT4 levels in the HG-HT group were significantly lower than those of the controls, whereas the FT3 levels and FT3/FT4 ratios were significantly higher in the HG-HT group. The FT3/FT4 ratios in the HG-HT group who had undergone total thyroidectomy and received levothyroxine therapy decreased significantly to normal values. Both the D1 and D2 activities in the thyroid tissues of the HG-HT patients were significantly higher than those of the controls. However, the mRNA levels of both D1 and D2 in the HG-HT patients' thyroid tissues were comparable to those of the controls. Interestingly, there were significant correlations between the HG-HT patients' D1 and D2 activities, and their thyroid gland volume or their FT3/FT4 ratios.

CONCLUSIONS

Our results indicate that increased thyroidal D1 and D2 activities may be responsible for the higher serum FT3/FT4 ratio in patients with HG-HT.

Effect of antithyroid drugs on the occurrence of antibodies against type 2 deiodinase (DIO2), which are involved in hyperthyroid Graves' disease influencing the therapeutic efficacy

Graves' disease is an organ-specific autoimmune disease with hyperthyroidism, diffuse goiter and autoantibodies against TSH receptor, thyroid peroxidase (TPO) and/or thyroglobulin (Tg). Graves' hyperthyroidism is characterized by T3 dominance due to the conversion of T4 into T3 through type 1 and 2 deiodinase enzymes (DIO1, DIO2). Methimazole (MMI) and propylthiouracil (PTU) therapies inhibit thyroid hormone synthesis blocking the activity of deiodinase and TPO enzymes. The study investigated the occurrence of autoantibodies against DIO2 peptides (cys- and hom-peptides) with the effect of antithyroid drugs on their frequencies in 78 patients with Graves' disease and 30 controls. In hyperthyroidism, the presence of DIO2 peptide antibodies was as follows: 20 and 11 cases out of 51 for cys- and hom-peptide antibodies, respectively, of whom 8 cases possessed antibodies against both peptides. Antithyroid drugs differently influenced their frequencies, which were greater in PTU than in MMI (3/6 vs 13/45 cases, P < 0.016 for cys- and 0/6 vs 2/45 cases for hom-peptide antibodies). Antibodies against both peptides demonstrated more reduced levels of anti-TPO (P < 0.003) and anti-Tg antibodies (P < 0.002) compared with those without peptide antibodies. PTU compared with MMI increased the levels of TSH receptor antibodies (32.5 UI/l vs 2.68 IU/l, P < 0.009). MMI treatment led to more reduced FT3 levels and FT3/FT4 ratios in hyperthyroid Graves' ophthalmopathy (P < 0.028 for FT3, P < 0.007 for FT3/FT4 ratio). In conclusion, the presence of DIO2 peptide antibodies is connected to Graves' hyperthyroidism influencing the levels of antibodies against TPO, Tg and TSH receptor, as well as the therapeutic efficacy of antithyroid drugs.

Review of oral cholecystographic agents for the management of hyperthyroidism

OBJECTIVE

Although the use of oral cholecystographic agents (OCAs) had declined due to limited availability, there is literature to suggest it is an effective medication for thyrotoxicosis in appropriate clinical situations.

METHODS

The authors performed a PubMed search and systematically reviewed all the English written case reports, original studies and reviews from 1953 to 2012. Additional information was supplemented from available online pharmacologic databases.

RESULTS

The off-label use of OCAs was reviewed for the management of neonatal and adult Graves' disease, subacute thyroiditis, amiodarone-induced thyroiditis (AIT), exogenous hyperthyroidism, toxic multinodular goiter (TMNG), thyrotropinoma, thyrotoxicosis during pregnancy, rapid pre-operative control of hyperthyroidism, and thyroid storm. Adverse effects were also reviewed.

CONCLUSION

OCAs generally are effective agents in treating thyrotoxicosis in the etiologies reviewed. OCAs are clinically relevant in patients who require rapid control, such as in the pre-operative state or patient who cannot tolerate a thyrotoxicosis state. OCA may also be beneficial in situations where other anti-thyroidal medication would be hazardous or ineffective, such as thionamide allergy or exogenous thyrotoxicosis. Given concern for long-term relapse, OCAs should be considered a short-term bridge to definitive therapy. OCAs are limited in TMNG and should be second line after glucocorticoids in AIT II. OCAs do not preclude the use of radioactive iodine, which can be performed one week after OCA therapy.

MANAGEMENT OF THYROTOXICOSIS: PRECONCEPTION, PREGNANCY, AND THE POSTPARTUM PERIOD

OBJECTIVE

To review the diagnosis and management of thyrotoxicosis in women who are preconception, pregnant, and in the postpartum period.

METHODS

Literature review of English-language papers published between 1980 and 2018.

RESULTS

Overt thyrotoxicosis occurs in 0.2% of pregnancies and subclinical thyrotoxicosis in 2.5%. Hyperthyroidism in women of childbearing age most frequently is caused by Graves disease (GD). Gestational thyrotoxicosis, transient human chorionic gonadotropin (hCG)-mediated hyperthyroidism, may develop in the first trimester. In the first year following delivery, postpartum thyroiditis, which frequently includes a thyrotoxic phase, occurs in 5% of women. Hyperthyroidism from nodular autonomy is uncommon in women of childbearing age. It is essential to understand the underlying etiology for thyrotoxicosis in order to recommend appropriate treatment. Gestational thyrotoxicosis requires supportive care, without antithyroid drug therapy. GD may be treated with antithyroid drugs, radioactive iodine, or thyroidectomy. Pregnancy, plans for pregnancy, and lactation have important implications for the choice of GD treatment. When thyrotoxicosis presents following delivery, postpartum thyroiditis must be differentiated from GD.

CONCLUSION

The diagnosis and management of thyrotoxicosis in the peripregnancy period present specific challenges. In making management decisions, it is essential to weigh the risks and benefits of treatments not just for the mother but also for the fetus and for breastfed infants. A team approach to management is critical, with close collaboration among endocrinologists, maternal-fetal medicine specialists, and neonatologists.

ABBREVIATIONS

GD = Graves disease; hCG = human chorionic gonadotropin; MMI = methimazole; PPT = postpartum thyroiditis; PTU = propylthiouracil; T3 = triiodothyronine; T4 = thyroxine; TBG = thyroxine-binding globulin; TRAb = TSH receptor antibody; TSH = thyroid-stimulating hormone.

Therapy with propylthiouracil for T3-predominant neonatal Graves' disease: a case report

This case report describes a male neonate with Graves’ disease. The mother’s pregnancy was complicated by poorly controlled Graves’ disease. The neonate was diagnosed with thyroxine (T3)-predominant Graves’ disease with low free triiodothyronine (T4) and high free T3 during antithyroid drug therapy. The patient also presented with persistent pulmonary hypertension of the newborn due to hyperthyroidism and airway stenosis caused by goiter. It was difficult to control thyroid function and maintain free T4 levels with inorganic iodine, thiamazole, and levothyroxine sodium hydrate. We successfully controlled thyroid function using the previous treatments in combination with propylthiouracil. Propylthiouracil suppresses type 1 iodothyronine deiodinase, and its pharmacological action suppresses the conversion of T4 to T3. Therefore, we used propylthiouracil at an earlier stage of intervention in this case. We ceased administration of antithyroid drugs on day 85 of life. Subsequently, as the TRH loading test revealed central hypothyroidism, oral administration of levothyroxine sodium hydrate was continued. Its administration was discontinued at the age of 1 yr. Thyroid-stimulating hormone recovered to normal values, and his development had progressed without complications by the age of 2 yr.

Diagnostic Values of Free Triiodothyronine and Free Thyroxine and the Ratio of Free Triiodothyronine to Free Thyroxine in Thyrotoxicosis

BACKGROUND

The results of previous studies on the usefulness of free triiodothyronine (FT3) to free thyroxine (FT4) are controversial. We investigated the usefulness of FT3, FT4, and FT3/FT4 ratio in differentiating Graves' disease (GD) from destructive thyroiditis.

METHODS

A total of 126 patients with untreated GD, 36 with painless thyroiditis, 18 with painful subacute thyroiditis, and 63 healthy controls, were recruited. The levels of FT3 and FT4 and the FT3/FT4 ratios for the different etiologies of thyrotoxicosis were evaluated separately by receiver operating characteristic (ROC) curve analysis. The expression levels of type 1 and type 2 deiodinase (DIO1 and DIO2) in thyroid tissues were also investigated.

RESULTS

The optimal cut-off values were 7.215 pmol/L for FT3, 21.71 pmol/L for FT4, and 0.4056 for the FT3/FT4 ratio. The specificity and positive predictive value of the FT3/FT4 ratio were highest for values > 0.4056. DIO1 mRNA expression was significantly higher in the thyroid tissue of patients with GD (P = 0.013).

CONCLUSIONS

We demonstrated that the FT3/FT4 ratio was useful in differentiating GD from destructive thyroiditis. In addition, a relatively high expression of type 1 deiodinase in the thyroid might be responsible for the high FT3/FT4 ratio in patients with GD.

Changes in Body Compositions and Basal Metabolic Rates during Treatment of Graves' Disease

OBJECTIVES

Because thyroid hormone is an important determinant of body weight and basal metabolic rate, we investigated the changes in the basal metabolic rate and body composition sequentially after treatment for Graves' disease.

METHODS

A prospective cohort study was performed with six women newly diagnosed with Graves' disease. During a 52-week treatment of methimazole, body composition, resting respiratory expenditure (REE), and handgrip strength were measured consecutively.

RESULTS

After methimazole treatment, body weight was initially increased (0-8 weeks), subsequently plateaued (8-24 weeks), and gradually decreased in the later period (24-52 weeks) despite the decreased food intake. The measured REE was 40% higher than the predicted REE at baseline, and it gradually decreased after treatment. REE positively correlated with thyroid hormone levels, peripheral deiodinase activity, and thyroid's secretory capacity. Body compositional analyses showed that the fat mass increased during an earlier period (4-12 weeks), while the lean mass increased significantly during the later period (26-52 weeks). Consistent with the lean mass changes, muscle strength also significantly increased during the later period.

CONCLUSIONS

Treatment of Graves' disease increased body weight and fat mass transiently with decreased REE. However, long-term compositional changes moved in a beneficial direction increasing lean mass and reinforcing muscle strength, following decreasing fat percentages.

Exogenous T3 toxicosis following consumption of a contaminated weight loss supplement

A 42-year-old male presented with a one-week history of palpitations and sweating episodes. The only significant history was of longstanding idiopathic dilated cardiomyopathy. Initial ECG demonstrated a sinus tachycardia. Thyroid function testing, undertaken as part of the diagnostic workup, revealed an un-measureable thyroid-stimulating hormone (TSH) and free thyroxine (T₄). Upon questioning the patient reported classical thyrotoxic symptoms over the preceding weeks. Given the persistence of symptoms free tri-iodothyronine (T₃) was measured and found to be markedly elevated at 48.9 pmol/L (normal range: 3.1-6.8 pmol/L). No goitre or nodular disease was palpable in the neck. Historically there had never been any amiodarone usage. Radionucleotide thyroid uptake imaging (¹²³I) demonstrated significantly reduced tracer uptake in the thyroid. Upon further questioning the patient reported purchasing a weight loss product online from India which supposedly contained sibutramine. He provided one of the tablets and laboratory analysis confirmed the presence of T₃ in the tablet. Full symptomatic resolution and normalised thyroid function ensued upon discontinuation of the supplement.

LEARNING POINTS

Free tri-iodothyronine (T₃) measurement may be useful in the presence of symptoms suggestive of thyrotoxicosis with discordant thyroid function tests.Thyroid uptake scanning can be a useful aid to differentiating exogenous hormone exposure from endogenous hyperthyroidism.Ingestion of thyroid hormone may be inadvertent in cases of exogenous thyrotoxicosis.Medicines and supplements sourced online for weight loss may contain thyroxine (T₄) or T₃ and should be considered as a cause of unexplained exogenous hyperthyroidism.

ENDOCRINOLOGY IN PREGNANCY: Pregnancy and the incidence, diagnosing and therapy of Graves' disease

Thyroid hormones are essential developmental factors, and Graves' disease (GD) may severely complicate a pregnancy. This review describes how pregnancy changes the risk of developing GD, how early pregnancy by several mechanisms leads to considerable changes in the results of the thyroid function tests used to diagnose hyperthyroidism, and how these changes may complicate the diagnosing of GD. Standard therapy of GD in pregnancy is anti-thyroid drugs. However, new studies have shown considerable risk of birth defects if these drugs are used in specific weeks of early pregnancy, and this should be taken into consideration when planning therapy and control of women who may in the future become pregnant. Early pregnancy is a period of major focus in GD, where pregnancy should be diagnosed as soon as possible, and where important and instant change in therapy may be warranted. Such change may be an immediate stop of anti-thyroid drug therapy in patients with a low risk of rapid relapse of hyperthyroidism, or it may be an immediate shift from methimazole/carbimazole (with risk of severe birth defects) to propylthiouracil (with less risk), or maybe to other types of therapy where no risk of birth defects have been observed. In the second half of pregnancy, an important concern is that not only the mother with GD but also her foetus should have normal thyroid function.

2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis

BACKGROUND

Thyrotoxicosis has multiple etiologies, manifestations, and potential therapies. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions and patient preference. This document describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspecialty physicians and others providing care for patients with this condition.

METHODS

The American Thyroid Association (ATA) previously cosponsored guidelines for the management of thyrotoxicosis that were published in 2011. Considerable new literature has been published since then, and the ATA felt updated evidence-based guidelines were needed. The association assembled a task force of expert clinicians who authored this report. They examined relevant literature using a systematic PubMed search supplemented with additional published materials. An evidence-based medicine approach that incorporated the knowledge and experience of the panel was used to update the 2011 text and recommendations. The strength of the recommendations and the quality of evidence supporting them were rated according to the approach recommended by the Grading of Recommendations, Assessment, Development, and Evaluation Group.

RESULTS

Clinical topics addressed include the initial evaluation and management of thyrotoxicosis; management of Graves' hyperthyroidism using radioactive iodine, antithyroid drugs, or surgery; management of toxic multinodular goiter or toxic adenoma using radioactive iodine or surgery; Graves' disease in children, adolescents, or pregnant patients; subclinical hyperthyroidism; hyperthyroidism in patients with Graves' orbitopathy; and management of other miscellaneous causes of thyrotoxicosis. New paradigms since publication of the 2011 guidelines are presented for the evaluation of the etiology of thyrotoxicosis, the management of Graves' hyperthyroidism with antithyroid drugs, the management of pregnant hyperthyroid patients, and the preparation of patients for thyroid surgery. The sections on less common causes of thyrotoxicosis have been expanded.

CONCLUSIONS

One hundred twenty-four evidence-based recommendations were developed to aid in the care of patients with thyrotoxicosis and to share what the task force believes is current, rational, and optimal medical practice.

Triiodothyronine-predominant Graves' disease in childhood: detection and therapeutic implications

OBJECTIVE

To assess in a pediatric population, the clinical characteristics and management of triiodothyronine-predominant Graves' disease (T3-P-GD), a rare condition well known in adults, but not previously described in children.

DESIGN

We conducted a university hospital-based observational study.

METHODS

All patients with GD followed for more than 1 year between 2003 and 2013 (n=60) were included. T3-P-GD (group I) was defined as high free T3 (fT3) concentration (>8.0 pmol/l) associated with a normal free thyroxine (fT4) concentration and undetectable TSH more than 1 month after the initiation of antithyroid drug (ATD) treatment. Group II contained patients with classical GD without T3-P-GD.

RESULTS

Eight (13%) of the patients were found to have T3-P-GD, a median of 6.3 (3.0-10.5) months after initial diagnosis (n=4) or 2.8 (2.0-11.9) months after the first relapse after treatment discontinuation (n=4). At GD diagnosis, group I patients were more likely to be younger (6.8 (4.3-11.0) vs 10.7 (7.2-13.7) years) and had more severe disease than group II patients, with higher serum TSH receptor autoantibodies (TRAb) levels: 40 (31-69) vs 17 (8-25) IU/l, P<0.04, and with slightly higher serum fT4 (92 (64-99) vs 63 (44-83) pmol/l) and fT3 (31 (30-46) vs 25 (17-31) pmol/l) concentrations. During the 3 years following T3-P-GD diagnosis, a double dose of ATD was required and median serum fT4:fT3 ratio remained lower in group I than in group II.

CONCLUSION

Severe hyperthyroidism, with particularly high TRAb concentrations at diagnosis, may facilitate the identification of patients requiring regular serum fT3 determinations and potentially needing higher doses of ATD dosage during follow-up.

Relapse following antithyroid drug therapy for Graves' hyperthyroidism

PURPOSE OF REVIEW

In most patients with hyperthyroidism caused by Graves' disease, antithyroid drug (ATD) therapy is followed by a gradual amelioration of the autoimmune abnormality, but about half of the patients will experience relapse of hyperthyroidism when the ATDs are withdrawn after a standard 1 to 2 years of therapy. This is a major drawback of ATD therapy, and a major concern to patients. We review current knowledge on how to predict and possibly reduce the risk of such relapse.

RECENT FINDINGS

Several patient and disease characteristics, as well as environmental factors and duration of ATD therapy, may influence the risk of relapse after ATD withdrawal. Depending on the presence of such factors, the risk of relapse after ATD withdrawal may vary from around 10 to 90%. Risk factors for relapse should be taken into account when choosing between therapeutic modalities in a patient with newly diagnosed disease, and also when discussing duration of ATD therapy.

SUMMARY

Prolonged low-dose ATD therapy may be feasible in patients with high risk of relapse, such as children and patients with active Graves' orbitopathy, and in patients with previous relapse who prefer such therapy rather than surgery or radioiodine.

The Brazilian consensus for the diagnosis and treatment of hyperthyroidism: recommendations by the Thyroid Department of the Brazilian Society of Endocrinology and Metabolism

INTRODUCTION

Hyperthyroidism is characterized by increased synthesis and release of thyroid hormones by the thyroid gland. Thyrotoxicosis refers to the clinical syndrome resulting from excessive circulating thyroid hormones, secondary to hyperthyroidism or due to other causes. This article describes evidence-based guidelines for the clinical management of thyrotoxicosis.

OBJECTIVE

This consensus, developed by Brazilian experts and sponsored by the Department of Thyroid Brazilian Society of Endocrinology and Metabolism, aims to address the management, diagnosis and treatment of patients with thyrotoxicosis, according to the most recent evidence from the literature and appropriate for the clinical reality of Brazil.

MATERIALS AND METHODS

After structuring clinical questions, search for evidence was made available in the literature, initially in the database MedLine, PubMed and Embase databases and subsequently in SciELO - Lilacs. The strength of evidence was evaluated by Oxford classification system was established from the study design used, considering the best available evidence for each question.

RESULTS

We have defined 13 questions about the initial clinical approach for the diagnosis and treatment that resulted in 53 recommendations, including the etiology, treatment with antithyroid drugs, radioactive iodine and surgery. We also addressed hyperthyroidism in children, teenagers or pregnant patients, and management of hyperthyroidism in patients with Graves' ophthalmopathy and various other causes of thyrotoxicosis.

CONCLUSIONS

The clinical diagnosis of hyperthyroidism usually offers no difficulty and should be made with measurements of serum TSH and thyroid hormones. The treatment can be performed with antithyroid drugs, surgery or administration of radioactive iodine according to the etiology of thyrotoxicosis, local availability of methods and preferences of the attending physician and patient.

Fibroblast growth factor 21 and thyroid hormone show mutual regulatory dependency but have independent actions in vivo

Thyroid hormone (TH) regulates fibroblast growth factor 21 (FGF21) levels in the liver and in the adipose tissue. In contrast, peripheral FGF21 administration leads to decreased circulating levels of TH. These data suggest that FGF21 and TH could interact to regulate metabolism. In the present study, we confirmed that TH regulates adipose and hepatic FGF21 expression and serum levels in mice. We next investigated the influence of TH administration on key serum metabolites, gene expression in the liver and brown adipose tissue, and energy expenditure in FGF21 knockout mice. Surprisingly, we did not observe any significant differences in the effects of TH on FGF21 knockout mice compared with those in wild-type animals, indicating that TH acts independently of FGF21 for the specific outcomes studied. Furthermore, exogenous FGF21 administration to hypothyroid mice led to similar changes in serum and liver lipid metabolites and gene expression in both hypothyroid and euthyroid mice. Thus, it appears that FGF21 and TH have similar actions to decrease serum and liver lipids despite having some divergent regulatory effects. Whereas TH leads to up-regulation in the liver and down-regulation in brown adipose tissue of genes involved in the lipid synthesis pathway (eg, fatty acid synthase (FASN) and SPOT14), FGF21 leads to the opposite changes in expression of these genes. In conclusion, TH and FGF21 act independently on the outcomes studied, despite their ability to regulate each other's circulating levels. Thus, TH and FGF21 may modulate the availability of each other in critical metabolic states.

Association between TSH-Receptor Autoimmunity, Hyperthyroidism, Goitre, and Orbitopathy in 208 Patients Included in the Remission Induction and Sustenance in Graves' Disease Study

Background. Graves' disease may have a number of clinical manifestations with varying degrees of activity that may not always run in parallel. Objectives. To study associations between serum levels of TSH-receptor autoantibodies and the three main manifestations of Graves' disease (hyperthyroidism, goiter, and presence of orbitopathy) at the time of diagnosis of hyperthyroidism. Methods. We describe a cohort of 208 patients with newly diagnosed Graves' hyperthyroidism. Patients were enrolled in a multiphase study of antithyroid drug therapy of Graves' hyperthyroidism, entitled "Remission Induction and Sustenance in Graves' Disease (RISG)." Patients were systematically tested for degree of biochemical hyperthyroidism, enlarged thyroid volume by ultrasonography, and the presence of orbitopathy. Results. Positive correlations were found between the levels of TSH-receptor autoantibodies in serum and the three manifestations of Graves' disease: severeness of hyperthyroidism, presence of enlarged thyroid, and presence of orbitopathy, as well as between the different types of manifestations. Only around half of patients had enlarged thyroid gland at the time of diagnosis of hyperthyroidism, whereas 25-30% had orbitopathy. Conclusions. A positive but rather weak correlation was found between TSH-receptor antibodies in serum and the major clinical manifestation of Graves' disease. Only half of the patients had an enlarged thyroid gland at the time of diagnosis.

Hyperthyroidism in pregnancy

Changes in thyroid hormone concentrations that are characteristic of hyperthyroidism must be distinguished from physiological changes in thyroid hormone economy that occur in pregnancy, especially in the first trimester. Approximately one to two cases of gestational hyperthyroidism occur per 1000 pregnancies. Identification of hyperthyroidism in a pregnant woman is important because adverse outcomes can occur in both the mother and the offspring. Graves' disease, which is autoimmune in nature, is the usual cause; but hyperthyroidism in pregnancy can be caused by any type of hyperthyroidism--eg, toxic multinodular goitre or solitary autonomously functioning nodule. Gestational transient thyrotoxicosis is typically reported in women with hyperemesis gravidarum, and is mediated by high circulating concentrations of human chorionic gonadotropin. Post-partum thyroiditis occurs in 5-10% of women, and many of those affected ultimately develop permanent hypothyroidism. Antithyroid drug treatment of hyperthyroidism in pregnant women is controversial because the usual drugs--methimazole or carbimazole--are occasionally teratogenic; and the alternative--propylthiouracil--can be hepatotoxic. Fetal hyperthyroidism can be life-threatening, and needs to be recognised as soon as possible so that treatment of the fetus with antithyroid drugs via the mother can be initiated. In this Review, we discuss physiological and pathophysiological changes in thyroid hormone economy in pregnancy, the diagnosis and management of hyperthyroidism during pregnancy, severe life-threatening thyrotoxicosis in pregnancy, neonatal thyrotoxicosis, and post-partum hyperthyroidism.

Determinants of serum T4 and T3 at the time of diagnosis in nosological types of thyrotoxicosis: a population-based study

OBJECTIVE

To characterize thyroid hormone levels at the time of diagnosis in the nosological types of thyrotoxicosis diagnosed in the population and to analyze determinants for serum thyroxine (T4) and tri-iodothyronine (T3).

DESIGN

Population-based study of thyrotoxicosis at disease onset.

METHODS

In the period 1997-2000, we prospectively identified all patients diagnosed with incident primary overt thyrotoxicosis in a Danish population cohort and classified patients into ten well-defined nosological types of disease (n=1082). Untreated levels of serum T3, T4, and T3:T4 ratio were compared and related to sex, age, level of iodine deficiency, smoking status, alcohol intake, iodine supplement use, co-morbidity, and TSH receptor antibodies (TRAbs) in multivariate models.

RESULTS

Graves' disease (GD) patients had much higher levels of T3 and higher T3:T4 ratio at diagnosis compared with other thyrotoxic patients, but with a profound negative association between hormone levels and age. In GD, patients diagnosed in the area with more severe iodine deficiency had lower levels of T3 and T4. TRAb-negative GD patients had biochemically mild thyrotoxicosis. Higher age was also associated with lower degree of biochemical thyrotoxicosis in nodular toxic goiter. We found no association between serum T3 and T4 and sex, smoking habits, iodine supplements, alcohol intake, or co-morbidity in any type of thyrotoxicosis.

CONCLUSIONS

The study gives new insight into the hormonal presentation of thyrotoxicosis and showed that young age, positive TRAb levels, but also residency in the area with higher iodine intake was positively associated with biochemical disruption in GD.

A Case of simultaneous occurrence of Marine - Lenhart syndrome and a papillary thyroid microcarcinoma

BACKGROUND

Marine-Lenhart syndrome is defined as the co-occurrence of Graves' disease and functional nodules. The vast majority of autonomous adenomas are benign, whereas functional thyroid carcinomas are considered to be rare. Here, we describe a case of simultaneous occurrence of Marine-Lenhart syndrome and a papillary microcarcinoma embedded in a functional nodule.

CASE PRESENTATION

A 55 year-old, caucasian man presented with overt hyperthyroidism (thyrotropin (TSH) <0.01 μIU/L; free thyroxine (FT4) 3.03 ng/dL), negative thyroid peroxidase and thyroglobulin autoantibodies, but elevated thyroid stimulating hormone receptor antibodies (TSH-RAb 2.6 IU/L). Ultrasound showed a highly vascularized hypoechoic nodule (1.1 × 0.9 × 2 cm) in the right lobe, which projected onto a hot area detected in the 99mtechnetium thyroid nuclear scan. Overall uptake was increased (4.29%), while the left lobe showed lower tracer uptake with no visible background-activity, supporting the notion that both Graves' disease and a toxic adenoma were present. After normal thyroid function was reinstalled with methimazole, the patient underwent thyroidectomy. Histological work up revealed a unifocal papillary microcarcinoma (9 mm, pT1a, R0), positively tested for the BRAF V600E mutation, embedded into the hyperfunctional nodular goiter.

CONCLUSIONS

Neither the finding of an autonomously functioning thyroid nodule nor the presence of Graves' disease rule out papillary thyroid carcinoma.

Thyroid function and obesity

Important interaction exists between thyroid function, weight control, and obesity. Several mechanisms seem to be involved, and in studies of groups of people the pattern of thyroid function tests depends on the balance of obesity and underlying thyroid disease in the cohort studied. Obese people with a normal thyroid gland tend to have activation of the hypothalamic-pituitary-thyroid axis with higher serum TSH and thyroid hormones in serum. On the other hand, small differences in thyroid function are associated with up to 5 kg difference in body weight. The weight loss after therapy of overt hypothyroidism is caused by excretion of water bound in tissues (myxoedema). Many patients treated for hyperthyroidism experience a gain of more weight than they lost during the active phase of the disease. The mechanism for this excessive weight gain has not been fully elucidated. New studies on the relation between L-T3 therapy and weight control are discussed. The interaction between weight control and therapy of thyroid disease is important to many patients and it should be studied in more detail.

Catalysis leads to posttranslational inactivation of the type 1 deiodinase and alters its conformation

Previously, it was shown that the type 1 deiodinase (D1) is subject to substrate-dependent inactivation that is blocked by pretreatment with the inhibitor of D1 catalysis, propylthiouracil (PTU). Using HepG2 cells with endogenous D1 activity, we found that while considerable D1-mediated catalysis of reverse tri-iodothyronine (rT(3)) is observed in intact cells, there was a significant loss of D1 activity in sonicates assayed from the same cells in parallel. This rT(3)-mediated loss of D1 activity occurs despite no change in D1 mRNA levels and is blocked by PTU treatment, suggesting a requirement for catalysis. Endogenous D1 activity in sonicates was inactivated in a dose-dependent manner in HepG2 cells, with a ∼50% decrease after 10 nM rT(3) treatment. Inactivation of D1 was rapid, occurring after only half an hour of rT(3) treatment. D1 expressed in HEK293 cells was inactivated by rT(3) in a similar manner. (75)Se labeling of the D1 selenoprotein indicated that after 4 h rT(3)-mediated inactivation of D1 occurs without a corresponding decrease in D1 protein levels, though rT(3) treatment causes a loss of D1 protein after 8-24 h. Bioluminescence resonance energy transfer studies indicate that rT(3) exposure increases energy transfer between the D1 homodimer subunits, and this was lost when the active site of D1 was mutated to alanine, suggesting that a post-catalytic structural change in the D1 homodimer could cause enzyme inactivation. Thus, both D1 and type 2 deiodinase are subject to catalysis-induced loss of activity although their inactivation occurs via very different mechanisms.

Positive correlation between type 1 and 2 iodothyronine deiodinases activities in human goiters

Type 1 (D1) and 2 (D2) iodothyronine deiodinases are selenocysteine-containing enzymes that catalyze the deiodination of T4 to T3 in the thyroid and in peripheral tissues. Despite their importance to the plasma T3 pool in human beings, there are few studies about their behavior in human thyroids. In order to better understand iodothyronine deiodinase regulation in the thyroid gland, we studied thyroid tissue samples from follicular adenoma (AD, n = 5), toxic diffuse goiter (TDG, n = 6), nontoxic multinodular goiter (NMG, n = 40), papillary thyroid carcinoma (PTC, n = 8), and surrounding normal tissues (NT, n = 7) from 36 patients submitted to elective thyroidectomy. D1 and D2 activities were determined by quantification of the radioiodine released by ¹²⁵I-rT3 or ¹²⁵I-T4 under standardized conditions, and expressed as pmol rT3 deiodinated per minute and mg protein (pmol rT3 min⁻¹ mg⁻¹ ptn) and fmol T4 deiodinated per minute and mg protein (fmol T4 min⁻¹ mg⁻¹ ptn), respectively. D1 activity detected in TDG and AD tissues were significantly higher than in NT, PTC or NMG samples. D2 activity was also significantly higher in TDG and AD samples than in PTC, NMG, or NT. There was great variability in D1 and D2 enzymatic activities from distinct patients as well as from different areas from the same goiter. There was a positive correlation (P < 0,0001, r = 0.4942) between D1 and D2 activities when all samples were taken into account, suggesting that-in the thyroid-these two iodothyronine deiodinases may have related regulatory mechanisms, even if conditioned by other as yet unknown factors.

Changes within the thyroid axis after long-term TSH-suppressive levothyroxine therapy

OBJECTIVE

The effects of long-term TSH-suppressive levothyroxine (LT4) therapy on thyroid hormone metabolism in patients with differentiated thyroid carcinoma (DTC) are unknown. The aim of the study was to investigate the changes in thyroid hormone metabolism after long-term TSH-suppressive LT4 therapy in patients with DTC.

PATIENTS AND METHODS

Sixty one patients with DTC were followed. For each patient, frozen remnant sera from two time points were selected: time1 (drawn within 1 year of I-131 ablation; TSH on file <0·3 mIU/l; recruitment period 1999-2002) and time2 (last available sample with TSH on file <0·3 mIU/l; minimum of 3 years of continuous TSH-suppressive LT4-therapy on record). TSH, reverse triiodothyronine (rT3), total triiodothyronine (TT3) and total thyroxine (TT4) levels were measured at both time1 and time2, and relationships between these parameters were analysed.

RESULTS

Total triiodothyronine, TT4 and TSH levels were significantly reduced at time2 (P < 0·001), whereas LT4 dose, bodyweight and rT3 levels remained constant between time1 and time2. There were no significant changes in the relationship between the dose of LT4/kg bodyweight and TT4 levels (P = 0·14). TT4/TT3 was increased at time2 (P < 0·001), whereas TT4/rT3 and TT3/rT3 were significantly decreased at time2. There appeared to be no relationship of the effects found and advancing age.

CONCLUSION

After long-term TSH-suppressive LT4 therapy for DTC, there are significant changes in thyroid hormone metabolism, which are best explained by a combined downregulation of deiodinases subtypes 1 and 2 and an upregulation of deiodinase subtype 3.

Thyrotoxicosis

Hyperthyroidism describes the sustained increase in thyroid hormone biosynthesis and secretion by a thyroid gland with increased metabolism. Although the use of radioiodine scanning serves as a useful surrogate that may help characterize the cause of thyrotoxicosis, it only indirectly addresses the underlying physiologic mechanism driving the increase in serum thyroid hormones. In this article, thyrotoxic states are divided into increased or decreased thyroid metabolic function. In addition to the diagnosis, clinical presentation, and treatment of the various causes of hyperthyroidism, a section on functional imaging and appropriate laboratory testing is included.

The role of the iodothyronine deiodinases in the physiology and pathophysiology of thyroid hormone action

Thyroxine (T4) is a prohormone and must be activated to 3,5,3' triodothyronine (T3) by either the type 1 (D1) or 2 (D2) selenodeiodinase. A third deiodinase (D3) inactivates T3 or T4 by removal of an inner ring iodine. These reactions require both a deiodinase enzyme and a cofactor, probably a thiol, to reduce the oxidized selenolyl group in the active center of each deiodinase. Thus, deiodination rates depend on both the enzyme and cofactor. The source of most of the circulating T3 is D1-mediated, while D2 provides nuclear receptor-bound hormone. Using sensitive and specific assays, it has become apparent that both D2 and D3 are widespread throughout vertebrate tissues. The complex interactions between the activating D2 and the inactivating D3 in tissues expressing these two enzymes determine the intracellular T3 concentration. This provides enormous flexibility for both developmental and tissue regeneration processes, allowing exquisite control of intracellular T3 concentrations. The endogenous factors regulating the activity of these enzymes, such as the hedgehog proteins, FoxO3, or the wnt/β catenin pathway together with the actions of thyroid hormone transporters, direct adjustments of nuclear receptor bound T3 which in turn can control the balance between cellular proliferation and differentiation. Their actions provide dynamic flexibility to what appears on the surface to be a very static hormonal system.

Free thyroxine level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate in multiparous

Preterm birth is the most common reason for perinatal morbidity and mortality in the western world. It has been shown that in euthyreotic pregnant women with thyroid autoimmune antibodies, L-Thyroxine replacement reduces preterm delivery rate in singleton pregnancies. We investigated in a nonrandomized retrospective observational study whether L-Thyroxine replacement, maintaining maternal free thyroxine serum level in the high normal reference range prescribed for nonpregnant women also influences the rate of preterm delivery in women without thyroid autoimmune antibodies. As control group for preterm delivery rate, data from perinatal statistics of the State of Baden-Württemberg from 2006 were used. The preterm delivery rate in the study group was significantly reduced. The subgroup analysis shows no difference in primiparous but a decline in multiparous by approximately 61% with L-Thyroxine replacement. Maintaining free thyroxine serum level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate.

Iodothyronine deiodinases and cancer

Thyroid hormones (TH) regulate key cellular processes, including proliferation, differentiation, and apoptosis in virtually all human cells. Disturbances in TH pathway and the resulting deregulation of these processes have been linked with neoplasia. The concentrations of TH in peripheral tissues are regulated via the activity of iodothyronine deiodinases. There are 3 types of these enzymes: type 1 and type 2 deiodinases are involved in TH activation while type 3 deiodinase inactivates TH. Expression and activity of iodothyronine deiodinases are disturbed in different types of neoplasia. According to the limited number of studies in cancer cell lines and mouse models changes in intratumoral and extratumoral T3 concentrations may influence proliferation rate and metastatic progression. Recent findings showing that increased expression of type 3 deiodinases may lead to enhanced tumoral proliferation support the idea that deiodinating enzymes have the potential to influence cancer progression. This review summarizes the observations of impaired expression and activity in different cancer types, published to date, and the mechanisms behind these alterations, including impaired regulation via TH receptors, transforming growth factor-β, and Sonic-hedgehog pathway. Possible roles of deiodinases as cancer markers and potential modulators of tumor progression are also discussed.

Physiological role and regulation of iodothyronine deiodinases: a 2011 update

T4 is a prohormone secreted by the thyroid. T4 has a long half life in circulation and it is tightly regulated to remain constant in a variety of circumstances. However, the availability of iodothyronine selenodeiodinases allow both the initiation or the cessation of thyroid hormone action and can result in surprisingly acute changes in the intracellular concentration of the active hormone T3, in a tissue- specific and chronologically-determined fashion, in spite of the constant circulating levels of the prohormone. This fine-tuning of thyroid hormone signaling is becoming widely appreciated in the context of situations where the rapid modifications in intracellular T3 concentrations are necessary for developmental changes or tissue repair. Given the increasing availability of genetic models of deiodinase deficiency, new insights into the role of these important enzymes are being recognized. In this review, we have incorporated new information regarding the special role played by these enzymes into our current knowledge of thyroid physiology, emphasizing the clinical significance of these new insights.

Type 1 and type 2 iodothyronine deiodinases in the thyroid gland of patients with 3,5,3'-triiodothyronine-predominant Graves' disease

OBJECTIVE

3,5,3'-triiodothyronine-predominant Graves' disease (T(3)-P-GD) is characterized by a persistently high serum T(3) level and normal or even lower serum thyroxine (T(4)) level during antithyroid drug therapy. The source of this high serum T(3) level has not been clarified. Our objective was to evaluate the contribution of type 1 and type 2 iodothyronine deiodinase (D1 (or DIO1) and D2 (or DIO2) respectively) in the thyroid gland to the high serum T(3) level in T(3)-P-GD.

METHODS

We measured the activity and mRNA level of both D1 and D2 in the thyroid tissues of patients with T(3)-P-GD (n=13) and common-type GD (CT-GD) (n=18) who had been treated with methimazole up until thyroidectomy.

RESULTS

Thyroidal D1 activity in patients with T(3)-P-GD (492.7±201.3 pmol/mg prot per h) was significantly higher (P<0.05) than that in patients with CT-GD (320.7±151.9 pmol/mg prot per h). On the other hand, thyroidal D2 activity in patients with T(3)-P-GD (823.9±596.4 fmol/mg prot per h) was markedly higher (P<0.005) than that in patients with CT-GD (194.8±131.6 fmol/mg prot per h). There was a significant correlation between the thyroidal D1 activity in patients with T(3)-P-GD and CT-GD and the serum FT(3)-to-FT(4) ratio (r=0.370, P<0.05). Moreover, there was a strong correlation between the thyroidal D2 activity in those patients and the serum FT(3)-to-FT(4) ratio (r=0.676, P<0.001).

CONCLUSIONS

Our results suggest that the increment of thyroidal deiodinase activity, namely D1 and especially D2 activities, may be responsible for the higher serum FT(3)-to-FT(4) ratio in T(3)-P-GD.

Developmental regulation of gene expression in the thyroid gland of Xenopus laevis tadpoles

Thyroid hormones (TH) are the primary morphogen regulating amphibian metamorphosis. However, knowledge about molecular mechanisms regulating thyroid gland activity in anuran tadpoles is very scarce. In this study, we characterized gene expression profiles in thyroids of Xenopus laevis tadpoles during spontaneous metamorphosis. Using real-time PCR, elevated expression of slc5a5, tpo, tshr, and sar1a mRNAs was detected at late prometamorphic and climax stages. For dio2 and dio3 but not dio1, developmental regulation of thyroidal expression was evident from a strong up-regulation at late stages. Conversely, expression of the DNA replication markers mcm2 and pcna declined at climax stages. The presence of functional feedback mechanisms at premetamorphic stages was examined in two experiments. Stage 52 tadpoles were exposed for 72 h to 1.0 microg/l thyroxine (T4). This treatment caused reduced mRNA expression of slc5a5, tpo, and dio2, whereas no significant changes were detectable for tshr expression in thyroids and tshb expression in the pituitary. In another experiment, stage 46 tadpoles were treated with 20 mg/l sodium perchlorate (PER) for 5 and 10 days. Within this period of time, control tadpoles developed to stages 50 and 52, respectively. PER treatment resulted in up-regulation of slc5a5, tpo, and tshr mRNAs at both time points and increased dio2 mRNA expression at day 10. Effects of PER on thyroid histology were only apparent on day 10. Together, our analyses of thyroidal gene expression demonstrate a marked developmental regulation for functional markers of thyroid activity, two deiodinases as well as for DNA replication markers. Expression patterns detected in PER- and T4-treated tadpoles indicate that functional feedback signaling controlling thyroid activity is already active during premetamorphosis.