3,5,3'-Triiodothyronine thyrotoxicosis due to increased conversion of administered levothyroxine in patients with massive metastatic follicular thyroid carcinoma

Proportion of serum thyroid hormone concentrations within the reference ranges in athyreotic patients on levothyroxine monotherapy: a retrospective study

Background

In patients receiving thyroid-stimulating hormone (TSH) suppressive therapy with levothyroxine (LT₄) after total thyroidectomy for thyroid cancer, thyroid function tests should be performed to adjust the LT₄ dose. Specifically, serum TSH concentrations are commonly measured because TSH suppression is necessary according to thyroid cancer risk. The aim of the present study was to elucidate whether free thyroxine (FT₄) or free triiodothyronine (FT₃) indicates better for adjusting the dose in athyreotic patients on LT₄ monotherapy after total thyroidectomy.

Methods

We retrospectively studied the compatibility of free thyroid hormone (FT₄ and FT₃) concentrations with reference ranges in athyreotic patients on LT₄ monotherapy after total thyroidectomy.

Results

We identified 2210 consecutive patients from their medical records. Of these patients, 250 had both FT₄ and FT₃ concentrations in addition to TSH. Two hundred seven had serum TSH concentrations below the reference range (0.5–5.0 μIU/mL), while 43 had them within the reference range. In the 207 patients with TSH concentrations below the reference range, 61 patients (29.5%) had FT₄ concentrations within the reference range (0.9–1.7 ng/dL) and 146 patients (70.5%) had FT₄ concentrations above the reference range. In contrast, 10 patients (4.8%) had FT₃ concentrations below the reference range (2.3–4.0 pg/mL) and 8 (3.9%) had FT₃ concentrations above the reference range; 189 patients (91.3%) had concentrations within the reference range. Of the 43 patients with TSH concentrations within the reference range, 25 (58.1%) had FT₄ concentrations within the reference range and 18 (41.9%) had FT₄ concentrations above the reference range. While, 11 patients (25.6%) had FT₃ concentrations below the reference range and one (2.3%) had FT₃ concentrations above the reference range; hence, 31 patients (72.1%) had FT₃ concentrations within the reference range.

Conclusion

This study showed that measuring FT₃ concentrations rather than FT₄ concentrations as the subsequent parameter of thyroid function might be more useful for disease management in terms of the proportion of serum thyroid hormone concentrations within the reference ranges. Furthermore, FT₃ measurement could be useful in providing more detailed treatments, including avoiding more aggressive TSH suppressive therapy and identifying the presence of low T₃ syndrome in the background.

Poorly Differentiated Thyroid Carcinoma Coexisting with Graves' Disease Involving T3 Thyrotoxicosis due to Increased D1 and D2 Activities

Background: Poorly differentiated thyroid carcinoma is rare and patients are typically euthyroid. We report a novel rare case of poorly differentiated thyroid carcinoma with triiodothyronine (T3) thyrotoxicosis. Patient's Findings: A 77-year-old man presented to Kuma Hospital due to a neck tumor. A thyroid ultrasonography revealed a 220-mL mass in the right lobe. Laboratory data showed low serum thyrotropin (TSH), low free thyroxine (fT4), and high free T3 (fT3) levels. Anti-TSH receptor antibodies and thyroid-stimulating antibodies were positive. 131I scintigraphy showed diffuse uptake only in the left thyroid lobe. The patient underwent a total thyroidectomy and histological examination identified as poorly differentiated thyroid carcinoma. He was diagnosed with poorly differentiated thyroid carcinoma coexisting with Graves' disease. The tumor showed elevated type 1 iodothyronine deiodinases (D1) and type 2 iodothyronine deiodinases (D2) activities compared with that of the left thyroid lobe. Summary and Conclusions: Increased D1 and D2 activities in poorly differentiated carcinoma resulted in T3 toxicosis with a high serum fT3/fT4 ratio.

METASTATIC HÜRTHLE CELL CARCINOMA PRESENTING WITH LOW FREE THYROXINE, SEVERE HYPERCALCEMIA AND SPURIOUS GROWTH HORMONE PRODUCTION

Objective

Hürthle cell tumors constitute about 5% of thyroid neoplasms. They have malignant potential, behaving very aggressively compared to other differentiated thyroid cancers. The objective of this case report is to describe a case of a Hürthle cell carcinoma with a single large metastasis in the liver presenting almost 17 years after hemithyroidectomy. We highlight the difficulties in making a histologic diagnosis and the unpredictable nature of this cancer.

Methods

The patient history and biochemistry were detailed. Thyroid function tests analyzed on multiple platforms (single-photon emission computed tomography, dynamic magnetic resonance imaging, technetium-99m bone scan, and radioactive iodine) were used to aid biochemical and radiologic diagnosis.

Results

The patient's thyroid function test showed persistently low free thyroxine concentrations with normal thyroid stimulating hormone and free triiodothyronine, suggesting rapid deiodination in the context of a large liver lesion. Radiologic and morphologic appearances of the liver lesion led to an initial misdiagnosis of primary hepato-cellular carcinoma, revised to metastatic Hürthle cell carcinoma after positive immunochemistry. Nonparathyroid hormone-related intractable hypercalcemia of malignancy with an unusual pattern of elevated 1,25-dihydroxyvitamin D and raised fibroblast growth factor 23 concentrations culminated in his demise.

Conclusions

In Hürthle cell carcinomas treated with partial thyroidectomy, subsequent abnormal thyroid functions tests may herald a more sinister underlying diagnosis. The management of Hürthle cell carcinoma relies heavily on the initial histology results. Histologic diagnosis should be sought earlier in abnormal and suspicious distant masses. Malignant hypercalcemia poses a great challenge in delayed presentations and can prove resistant to conventional treatments.

Thyroid function related symptoms during levothyroxine monotherapy in athyreotic patients

Previous reports by us and other investigators showed that among athyreotic patients on levothyroxine (LT₄) following total thyroidectomy patients with normal serum thyroid-stimulating hormone (TSH) levels had mildly low serum free triiodothyronine (FT₃) levels, whereas patients with mildly suppressed serum TSH levels had normal serum FT₃ levels and patients with strongly suppressed serum TSH had elevated serum FT₃ levels. The objective of this study was to clarify which of these three patient groups are closer to their preoperative euthyroid condition based on reported subjective symptoms. We prospectively studied 148 consecutive euthyroid patients with papillary thyroid carcinoma who underwent a total thyroidectomy. Symptoms reflecting thyroid function documented preoperatively and following 12 months of LT₄ after thyroidectomy were compared. In 65 patients with strongly suppressed TSH levels significant changes in symptoms with tendencies towards thyrotoxicosis were seen with regards to heat and cold tolerance (p < 0.01), bowel movements (p < 0.05), and hand tremors (p < 0.05). In 33 patients with normal TSH levels, significant changes in symptoms with tendencies towards hypothyroidism were seen with regards to heat and cold tolerance (p < 0.05) and activity (p < 0.05). Lastly, in 50 patients with mildly suppressed TSH levels and FT₃ levels equivalent to preoperative levels, all symptom items remained equivalent to their preoperative levels. Symptoms reflecting thyroid function in patients on LT₄ following total thyroidectomy suggested that patients with mildly suppressed TSH levels were closest to a euthyroid status. These data provide useful findings regarding the management of patients following total thyroidectomy.

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.

Thyrotoxicosis with concomitant thyroid cancer

Thyrotoxicosis with concomitant thyroid cancer is rare and poorly recognized, which may result in delayed diagnosis, inappropriate treatment and even poor prognosis. To provide a comprehensive guidance for clinicians, the etiology, pathogenesis, diagnosis and treatment of this challenging setting were systematically reviewed. According to literatures available, the etiologies of thyrotoxicosis with concomitant thyroid cancer were categorized into Graves' disease with concurrent differentiated thyroid cancer (DTC) or medullary thyroid cancer, Marine-Lenhart Syndrome with coexisting DTC, Plummer's disease with concomitant DTC, amiodarone-induced thyrotoxicosis with concomitant DTC, central hyperthyroidism with coexisting DTC, hyperfunctioning metastases of DTC and others. The underlying causal mechanisms linking thyrotoxicosis and thyroid cancer were elucidated. Medical history, biochemical assessments, radioiodine uptake, anatomic and metabolic imaging and ultrasonography-guided fine-needle aspiration combined with pathological examinations were found to be critical for precise diagnosis. Surgery remains a mainstay in both tumor elimination and control of thyrotoxicosis, while anti-thyroid drugs, beta-blockers, 131I, glucocorticoids, plasmapheresis, somatostatin analogs, dopamine agonists, radiation therapy, chemotherapy and tyrosine kinase inhibitors should also be appropriately utilized as needed.

Thyrotoxicosis: Diagnosis and Management

Thyrotoxicosis is the clinical manifestation of excess thyroid hormone action at the tissue level due to inappropriately high circulating thyroid hormone concentrations. Hyperthyroidism, a subset of thyrotoxicosis, refers specifically to excess thyroid hormone synthesis and secretion by the thyroid gland. We performed a review of the literature on these topics utilizing published data in PubMed and MEDLINE. In this review, we discuss the more common etiologies of thyrotoxicosis, focusing on the current approach to diagnosis and management, new trends in those directions, and potential upcoming changes in the field.

A Case of Functional Metastatic Follicular Thyroid Carcinoma that Presented with Hip Fracture and Hypercalcemia

Thyroid follicular cancers are one of the thyroid gland cancers. This cancer can lead to metastases to various areas of the body. We describe a patient with thyroid follicular carcinoma who after total thyroidectomy had severe hypercalcemia, increased creatinine, and thyrotoxicosis due to extensive bone metastases. The patient was a 52-year-old man who had femoral neck fracture as the first manifestation of thyroid cancer. He was hospitalized for some time after orthopedic measures because of thyrotoxicosis and deep-venous thrombosis. The study found that the origin of metastatic lesions was thyroid follicular cancer, leading to extensive bone metastases. After administering of methimazole and control of thyrotoxicosis, he was subjected to total thyroidectomy. Methimazole was discontinued immediately after surgery. One month after surgery, ultrasound confirmed that the thyroid was completely removed. However, T3 (triiodothyronine) remained high; besides the patient had hypercalcemia and increased creatinine due to dehydration. The patient was retreated with methimazole due to thyrotoxicosis, and for hypercalcemia fluid therapy, intravenous zoledronic acid was prescribed. These measures led to the normalization of creatinine and glomerular filtration rate. The purpose of introducing this case report was that these symptoms are a rare manifestation of functional metastases of follicular thyroid carcinoma after total thyroidectomy. Bone metastases of follicular thyroid carcinoma may be functional and are lytic that can lead to hypercalcemia and its complications.

An upper cervical cord compression secondary to occult follicular thyroid carcinoma metastases successfully treated with multiple radioiodine therapies: A clinical case report

RATIONALE

The spine is the most common site of bone metastases due to thyroid cancer; however, spinal cord compression as a complication of metastatic thyroid cancer is very rare.

PATIENT CONCERNS

A 48-year-old female patient was presented to the Neurosurgical Department, complaining of progressive back neck pain with bilateral upper extremities numbness and weakness for 4 months.

DIAGNOSIS

Imaging studies revealed osteolytic destruction in bodies and accessories of the second and third cervical vertebrae with a huge soft-tissue mass compressing spinal cord and causing swelling. After the neurosurgical decompression surgery, the pathological examination established a metastatic follicular carcinoma originating from the thyroid gland.

INTERVENTIONS

Her cervical spinal metastases were hardly removed by surgery and the risks of external beam radiation therapy (EBRT) were very high. So she underwent a total thyroidectomy and received multiple radioiodine (RAI) and concomitant glucocorticoid therapies postoperatively. Radioiodine whole-body scan (WBS) showed multiple abnormal radioiodine uptakes. Then single-photon emission tomography/computed tomography (SPECT/CT) located these spinal metastases involving cervical, lumbar, and sacral vertebrae.

OUTCOMES

After 5 times RAI therapy, her thyroglobulin obviously decreased, with the cervical lesion shrinkage and no spinal cord edema.

LESSONS

RAI therapy and concomitant glucocorticoid therapy could be used for spinal metastases of FTC, even with spinal cord compression.

Biochemical Markers Reflecting Thyroid Function in Athyreotic Patients on Levothyroxine Monotherapy

BACKGROUND

Some investigators reported that among athyreotic patients on levothyroxine (LT4) monotherapy following total thyroidectomy, the patients with normal serum thyrotropin (TSH) levels had mildly low serum free triiodothyronine (fT3) levels, whereas the patients with mildly suppressed serum TSH levels had normal serum fT3 levels, and the patients with strongly suppressed serum TSH had elevated serum fT3 levels. The objective of the present study was to clarify which of these three patient groups is closer to their preoperative euthyroid condition.

METHODS

A total of 133 consecutive euthyroid patients with papillary thyroid carcinoma who underwent a total thyroidectomy were prospectively studied. The patients' serum levels of lipoproteins, sex hormone-binding globulin, and bone metabolic markers measured preoperatively were compared with the levels measured at postoperative LT4 therapy 12 months after the thyroidectomy.

RESULTS

The postoperative serum sex hormone-binding globulin (p < 0.001) and bone alkaline phosphatase (p < 0.01) levels were significantly increased in the patients with strongly suppressed TSH levels (≤0.03 μIU/mL). The postoperative serum low-density lipoprotein cholesterol levels were significantly increased (p < 0.05), and the serum tartrate-resistant acid phosphatase-5b levels were significantly decreased (p < 0.05) in the patients with normal TSH (0.3 < TSH ≤5 μIU/mL). In the patients with mildly suppressed TSH (0.03 < TSH ≤0.3 μIU/mL) and fT3 levels equivalent to their preoperative levels, all metabolic markers remained equivalent to their preoperative levels.

CONCLUSIONS

The serum biochemical markers of thyroid function in patients on LT4 following total thyroidectomy suggest that the patients with mildly suppressed TSH levels were closest to euthyroid, whereas those with normal TSH levels were mildly hypothyroid and those with strongly suppressed TSH levels were mildly hyperthyroid. These data may provide novel information on the management of patients following total thyroidectomy for thyroid cancer or benign thyroid disease.

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.

Calculated Parameters of Thyroid Homeostasis: Emerging Tools for Differential Diagnosis and Clinical Research

Although technical problems of thyroid testing have largely been resolved by modern assay technology, biological variation remains a challenge. This applies to subclinical thyroid disease, non-thyroidal illness syndrome, and those 10% of hypothyroid patients, who report impaired quality of life, despite normal thyrotropin (TSH) concentrations under levothyroxine (L-T4) replacement. Among multiple explanations for this condition, inadequate treatment dosage and monotherapy with L-T4 in subjects with impaired deiodination have received major attention. Translation to clinical practice is difficult, however, since univariate reference ranges for TSH and thyroid hormones fail to deliver robust decision algorithms for therapeutic interventions in patients with more subtle thyroid dysfunctions. Advances in mathematical and simulative modeling of pituitary-thyroid feedback control have improved our understanding of physiological mechanisms governing the homeostatic behavior. From multiple cybernetic models developed since 1956, four examples have also been translated to applications in medical decision-making and clinical trials. Structure parameters representing fundamental properties of the processing structure include the calculated secretory capacity of the thyroid gland (SPINA-GT), sum activity of peripheral deiodinases (SPINA-GD) and Jostel's TSH index for assessment of thyrotropic pituitary function, supplemented by a recently published algorithm for reconstructing the personal set point of thyroid homeostasis. In addition, a family of integrated models (University of California-Los Angeles platform) provides advanced methods for bioequivalence studies. This perspective article delivers an overview of current clinical research on the basis of mathematical thyroid models. In addition to a summary of large clinical trials, it provides previously unpublished results of validation studies based on simulation and clinical samples.

Effect of the presence of remnant thyroid tissue on the serum thyroid hormone balance in thyroidectomized patients

OBJECTIVE

We and others recently reported that in total thyroidectomy (TT), serum triiodothyronine (T3) levels during levothyroxine (L-T4) therapy were low compared to the preoperative levels, suggesting that the presence of the thyroid tissue affects the balances of serum thyroid hormone levels. However, the effects of remnant thyroid tissue on these balances in thyroidectomized patients have not been established.

METHODS

We retrospectively studied 253 euthyroid patients with papillary thyroid carcinoma who underwent a TT or hemithyroidectomy (HT). We divided the cases into the TT+supplemental L-T4 (+L-T4) group (n=103); the HT+L-T4 group (n=56); and the HT-alone group (n=94). We compared the postoperative serum levels of free T4 (FT4) and free T3 (FT3) and the FT3/FT4 ratio in individual patients with those of controls matched by serum TSH levels.

RESULTS

The TT+L-T4 group had significantly higher FT4 (P<0.001), lower FT3 (P<0.01) and lower FT3/FT4 (P<0.001) levels compared to the controls. The HT+L-T4 group had FT4, FT3 and FT3/FT4 levels equivalent to those of the controls. The HT-alone group had significantly lower FT4 (P<0.01), equivalent FT3 (P=0.083), and significantly higher FT3/FT4 (P<0.001) ratios than the controls.

CONCLUSIONS

The presence of the remnant thyroid tissue was associated with different thyroid hormone balances in thyroidectomized patients, suggesting that T3 production by remnant thyroid tissue has a substantial effect on the maintenance of postoperative serum T3 levels.

Clinical management and outcomes in patients with hyperfunctioning distant metastases from differentiated thyroid cancer after total thyroidectomy and radioactive iodine therapy

BACKGROUND

Hyperfunctioning distant metastasis (HFDM) from differentiated thyroid cancer (DTC) is a rare entity. This study aimed to assess the outcomes of DTC patients presenting with HFDM after total thyroidectomy and radioactive iodine therapy.

METHODS

A total of 5367 DTC patients treated with (131)I after total thyroidectomy were analyzed retrospectively from January 1991 to June 2013. Therapeutic efficacy was evaluated based on changes in serum thyroglobulin (Tg) and anatomical imaging changes in metastatic lesions. The relationships between survival time and several variables were assessed by univariate and multivariate analyses using the Kaplan-Meier method and Cox's proportional hazards model respectively.

RESULTS

Thirty-eight patients with HFDM from DTC were diagnosed, including four with hyperthyroidism, four with subclinical hyperthyroidism, and three with subclinical hypothyroidism. The remaining 27 were euthyroid. Of 25 patients with lung metastases, 84% (21/25) showed disappearance or shrinkage of lung nodules; of 24 patients with bone metastases, 66.67% (16/24) exhibited no obvious imaging changes in metastatic bone lesions after (131)I therapy. Serum Tg decreased significantly in 81.58% (31/38) and increased in 18.42% (7/38) after (131)I therapy. The 10-year survival rate of DTC patients with HFDM was 65.79% (25/38). Multivariate analyses identified age at occurrence of distant metastases (<45 years), only lung metastases, and papillary thyroid cancer (PTC; p=0.032, NA, and 0.043) as independent predictors of survival.

CONCLUSION

The response of hyperfunctioning lung metastases to (131)I treatment was better than that of non-hyperfunctioning lung metastases in DTC, while hyperfunctioning bone metastases responded similarly compared to non-hyperfunctioning bone metastases. Patients younger than 45 years at occurrence of distant metastases, those with only lung metastases, and patients with PTC had better prognoses.

A rare cause of hyperthyroidism: functioning thyroid metastases

Hyperthyroidism is a common medical problem that is readily treated with antithyroid medications. However, attributing the correct aetiology of hyperthyroidism alters management and outcome. We present a case of a 66-year-old woman with a seemingly common problem of hyperthyroidism associated with a goitre, which was initially attributed to a toxic nodule. However, Tc-99m pertechnetate uptake scan and thyroid-stimulating hormone receptor antibody were negative, inconsistent with a toxic nodule or Grave's disease. Her thyroid function tests proved difficult to control over the next few months. She eventually proceeded to a total thyroidectomy and histology revealed follicular variant papillary thyroid carcinoma. She was started on levothyroxine postoperatively but developed severe hyperthyroidism, revealing the cause of hyperthyroidism to be autonomously functioning thyroid metastases. Although functioning thyroid metastases are very rare, they need to be considered among the differential diagnoses of hyperthyroidism, as there are nuances in management that could alter the eventual outcome.

TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis

This paper provides the reader with an overview of our current knowledge of hypothalamic-pituitary-thyroid feedback from a cybernetic standpoint. Over the past decades we have gained a plethora of information from biochemical, clinical, and epidemiological investigation, especially on the role of TSH and other thyrotropic agonists as critical components of this complex relationship. Integrating these data into a systems perspective delivers new insights into static and dynamic behaviour of thyroid homeostasis. Explicit usage of this information with mathematical methods promises to deliver a better understanding of thyrotropic feedback control and new options for personalised diagnosis of thyroid dysfunction and targeted therapy, also by permitting a new perspective on the conundrum of the TSH reference range.

Euthyroid status after total thyroidectomy due to functioning lung metastases from a clear cell variant of papillary thyroid carcinoma

BACKGROUND

Although functioning thyroid cancer metastases have been reported, they have almost never been reported for the clear cell variant of papillary thyroid carcinoma (PTC). Here we describe a patient with disseminated lung metastases of the clear cell variant of PTC who presented in the euthyroid state despite discontinuance of levothyroxine after total thyroidectomy.

PATIENT FINDINGS

A 49-year-old woman underwent total thyroidectomy for the clear cell variant of PTC in March 2002. Levothyroxine replacement was initiated after total thyroidectomy, but the patient was lost to follow-up 5 years after the operation. She did not take any levothyroxine for 4 years. Upon presentation to our institution, her initial thyroid function tests were a serum thyroid-stimulating hormone (TSH) of 4.51 mIU/L (0.30-5.00), total triiodothyronine of 82 ng/dL (60-181), and free thyroxine of 1.21 ng/dL (0.89-1.76). The results of workups, including thyroid ultrasonography, chest computed tomography (CT) scan, and fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET)/CT, revealed that she had multiple metastases in the cervical lymph nodes and both lungs. She received 0.9 mg of recombinant human TSH (rhTSH) for 2 consecutive days followed by administration of 200 mCi 131I. A therapeutic whole body scan after 131I administration demonstrated intense uptake in the whole lung fields, suggesting functioning lung metastases.

SUMMARY

It is extremely rare for metastatic PTC, even though it is a well-differentiated thyroid carcinoma, to produce a sufficient amount of thyroid hormones to result in euthyroid state after total thyroidectomy. To our knowledge, this is the first report of functioning lung metastases of the clear cell variant of PTC after total thyroidectomy that produced enough thyroid hormone to restore a euthyroid state.

CONCLUSION

Functioning metastases from recurred PTC, particularly of the clear cell variant, are very rare. When they occur, rhTSH is required to prepare these patients for treatment with ablative doses of radioactive iodine (131I).

TSH-suppressive doses of levothyroxine are required to achieve preoperative native serum triiodothyronine levels in patients who have undergone total thyroidectomy

OBJECTIVE

Thyroidal production of triiodothyronine (T(3)) is absent in patients who have undergone total thyroidectomy. Therefore, relative T(3) deficiency may occur during postoperative levothyroxine (L-T(4)) therapy. The objective of this study was to evaluate how the individual serum T(3) level changes between preoperative native thyroid function and postoperative L-T(4) therapy.

METHODS

We retrospectively studied 135 consecutive patients with papillary thyroid carcinoma, who underwent total thyroidectomy. Serum free T(4) (FT(4)), free T(3) (FT(3)), and TSH levels measured preoperatively were compared with those levels measured on postoperative L-T(4) therapy.

RESULTS

serum tsh levels during postoperative L-T(4) therapy were significantly decreased compared with native TSH levels (P<0.001). serum FT(4) levels were significantly increased (P<0.001). Serum FT(3) levels were significantly decreased (P=0.029). We divided the patients into four groups according to postoperative serum TSH levels: strongly suppressed (less than one-tenth of the lower limit); moderately suppressed (between one-tenth of the lower limit and the lower limit); normal limit; and more than upper limit. Patients with strongly suppressed TSH levels had serum FT(3) levels significantly higher than the native levels (P<0.001). Patients with moderately suppressed TSH levels had serum FT(3) levels equivalent to the native levels (P=0.51), and patients with normal TSH levels had significantly lower serum FT(3) levels (P<0.001).

CONCLUSIONS

Serum FT(3) levels during postoperative L-T(4) therapy were equivalent to the preoperative levels in patients with moderately suppressed TSH levels. Our study indicated that a moderately TSH-suppressive dose of L-T(4) is required to achieve the preoperative native serum T(3) levels in postoperative L-T(4) therapy.

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.

Type II iodothyronine deiodinase provides intracellular 3,5,3'-triiodothyronine to normal and regenerating mouse skeletal muscle

The FoxO3-dependent increase in type II deiodinase (D2), which converts the prohormone thyroxine (T(4)) to 3,5,3'-triiodothyronine (T(3)), is required for normal mouse skeletal muscle differentiation and regeneration. This implies a requirement for an increase in D2-generated intracellular T(3) under these conditions, which has not been directly demonstrated despite the presence of D2 activity in skeletal muscle. We directly show that D2-mediated T(4)-to-T(3) conversion increases during differentiation in C(2)C(12) myoblast and primary cultures of mouse neonatal skeletal muscle precursor cells, and that blockade of D2 eliminates this. In adult mice given (125)I-T(4) and (131)I-T(3), the intracellular (125)I-T(3)/(131)I-T(3) ratio is significantly higher than in serum in both the D2-expressing cerebral cortex and the skeletal muscle of wild-type, but not D2KO, mice. In D1-expressing liver and kidney, the (125)I-T(3)/(131)I-T(3) ratio does not differ from that in serum. Hypothyroidism increases D2 activity, and in agreement with this, the difference in (125)I-T(3)/(131)I-T(3) ratio is increased further in hypothyroid wild-type mice but not altered in the D2KO. Notably, in wild-type but not in D2KO mice, the muscle production of (125)I-T(3) is doubled after skeletal muscle injury. Thus, D2-mediated T(4)-to-T(3) conversion generates significant intracellular T(3) in normal mouse skeletal muscle, with the increased T(3) required for muscle regeneration being provided by increased D2 synthesis, not by T(3) from the circulation.

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.

Thyrotoxicosis due to functioning metastatic follicular thyroid carcinoma after twelve I-131 therapies

We present a case of functioning metastatic follicular thyroid carcinoma (FTC) causing severe thyrotoxicosis despite four years 12 iodine-131 therapies (1.461 Ci cumulatively). Initially, the patient had ostalgia and fracture in the right femur. Surgery-confirmed metastatic bone FTC and thyroidectomy-confirmed FTC. One month later, iodine-131 treatment commenced. During the follow-up, different metastatic sites showed different outcomes. Lung metastases disappeared, a thigh metastasis persisted, a new metastasis in the head occurred and pelvic metastases deteriorated into a huge mass elevating thyroglobulin and causing thyrotoxicosis within 3 months. Presurgical PET/CT also demonstrated the massiveness of the pelvic metastases. Thyrotoxicosis disappeared after surgical removal of the pelvic lesion.

Minireview: Defining the roles of the iodothyronine deiodinases: current concepts and challenges

As is typical of other hormone systems, the actions of the thyroid hormones (TH) differ from tissue to tissue depending upon a number of variables. In addition to varying expression levels of TH receptors and transporters, differing patterns of TH metabolism provide a critical mechanism whereby TH action can be individualized in cells depending on the needs of the organism. The iodothyronine deiodinases constitute a family of selenoenzymes that selectively remove iodide from thyroxine and its derivatives, thus activating or inactivating these hormones. Three deiodinases have been identified, and much has been learned regarding the differing structures, catalytic activities, and expression patterns of these proteins. Because of their differing properties, the deiodinases appear to serve varying functions that are important in regulating metabolic processes, TH action during development, and feedback control of the thyroid axis. This review will briefly assess these functional roles and others proposed for the deiodinases and examine some of the current challenges in expanding our knowledge of these important components of the thyroid homeostatic system.