Metastatic thyroid cancer presenting as thyrotoxicosis: report of three cases

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.

A case of metastatic follicular thyroid carcinoma complicated with Graves' disease after total thyroidectomy

Thyroid cancer and Graves' disease may present simultaneously in one patient. The incidence of the development of hyperthyroidism from metastatic differentiated thyroid carcinoma is rare. We herein report a case of metastatic follicular carcinoma complicated with Graves' disease after total thyroidectomy. A 57-year-old woman underwent right hemithyroidectomy for follicular carcinoma. Metastatic lesions appeared in the lungs and skull two years after the first surgery, and remnant thyroidectomy was performed for radioactive iodine-131 (RAI) therapy, during which the TSH receptor antibody (TRAb) was found to be negative. The patient was treated with RAI therapy four times for four years and was receiving levothyroxine suppressive therapy. Although radioiodine uptake was observed in the lesions after the fourth course of RAI therapy, metastatic lesions had progressed. Four years after the second surgery, she had heart palpitations and tremors. Laboratory data revealed hyperthyroidism and positive TRAb. She was diagnosed with Graves' disease and received a fifth course of RAI therapy. 131I scintigraphy after RAI therapy showed strong radioiodine uptake in the metastatic lesions. As a result, the sizes and numbers of metastatic lesions decreased, and thyroid function improved. Metastatic lesions produced thyroid hormone and caused hyperthyroidism. RAI therapy was effective for Graves' disease and thyroid carcinoma.

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.

A case report of hyperfunctioning metastatic thyroid cancer and rare I-131 avid liver metastasis

Thyroid cancer is usually, relatively hypofunctional; most patients with thyroid cancer are clinically euthyroid. The combination of thyroid cancer and thyrotoxicosis is not common. We herein, report a case of follicular thyroid cancer with hyperfunctioning metastasis in a 43-year-old woman who presented with thyrotoxicosis, a cold right thyroid nodule, and low I-131 uptake at the thyroid bed. An additional total body scan with I-131 revealed a large radioiodine avid osteolytic bone metastasis with soft tissue masses and liver metastasis. The patient received treatment with total thyroidectomy, methimazole, and I-131 at a cumulative dose of 600 mCi along with recombinant human thyroid-stimulating hormone before the first I-131 treatment and palliative radiation. The patient had normal liver function test and experienced a mild degree of bone marrow suppression after I-131. At the 2-year follow-up, the patient was still alive with the progression of bone metastases but was doing well with less severe thyrotoxicosis, good ambulation, and an Eastern Cooperative Oncology Group performance status of 2. Clinicians should be aware of the unusual concurrent presentation of thyrotoxicosis and thyroid cancer, a differential diagnosis in patients with thyrotoxicosis and low or normal radioiodine uptake over the neck and also potential pitfalls during radionuclide treatment.

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.

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.

Incidental detection of hyperfunctioning thyroid cancer metastases in patients presenting with thyrotoxicosis

Thyrotoxicosis due to functioning metastases from thyroid cancer is rare. It also presents a therapeutic challenge, as both the metastatic cancer and thyrotoxicosis need to be treated. We present here two cases of thyrotoxicosis which on a routine (99m)Tc-pertechnetate thyroid scan showed extrathyroidal foci of uptake. Two patients who initially presented with thyrotoxicosis underwent a routine thyroid scan. Abnormal uptake in the shoulder was incidentally noted, which prompted us to do a whole body pertechnetate scan in the same sitting, which revealed extensive hyperfunctioning metastases in the lungs and bones. We also discuss the 'Flip Flop' phenomenon in thyroid cancer, which was seen in our case. This report emphasizes the importance of evaluating the abnormal foci of uptake seen on a routine thyroid scan.

Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists

OBJECTIVE

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 article describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspeciality physicians and others providing care for patients with this condition.

METHODS

The development of these guidelines was commissioned by the American Thyroid Association in association with the American Association of Clinical Endocrinologists. The American Thyroid Association and American Association of Clinical Endocrinologists assembled a task force of expert clinicians who authored this report. The task force 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 develop the text and a series of specific recommendations. The strength of the recommendations and the quality of evidence supporting each was 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' ophthalmopathy; and management of other miscellaneous causes of thyrotoxicosis.

CONCLUSIONS

One hundred 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.

Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists

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 article describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspeciality physicians and others providing care for patients with this condition.

METHODS

The development of these guidelines was commissioned by the American Thyroid Association in association with the American Association of Clinical Endocrinologists. The American Thyroid Association and American Association of Clinical Endocrinologists assembled a task force of expert clinicians who authored this report. The task force 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 develop the text and a series of specific recommendations. The strength of the recommendations and the quality of evidence supporting each was 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' ophthalmopathy; and management of other miscellaneous causes of thyrotoxicosis.

CONCLUSIONS

One hundred 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.

Hyperfunctioning solid/trabecular follicular carcinoma of the thyroid gland

A 68-year-old woman with solid/trabecular follicular thyroid carcinoma inside of an autonomously functioning thyroid nodule is described in this paper. The patient was referred to our clinic for swelling of the neck and an increased pulse rate. Ultrasonography showed a slightly hypoechoic nodule in the right lobe of the thyroid. Despite suppressed TSH levels, the ^99mTc-pertechnetate scan showed a hot area corresponding to the nodule with a suppressed uptake in the remaining thyroid tissue. Histopathological examination of the nodule revealed a solid/trabecular follicular thyroid carcinoma. To the best of our knowledge, this is the first case of hyperfunctioning follicular solid/trabecular carcinoma reported in the literature. Even if a hyperfunctioning thyroid carcinoma is an extremely rare malignancy, careful management is recommended so that a malignancy will not be overlooked in the hot thyroid nodules.

Thyrotoxicosis and low iodine uptake in a woman with graves' disease

Thyrotoxicosis factitia is defined as thyrotoxicosis resulting from exogenous ingestion of thyroid hormone, usually in patients with a psychiatric disorder. Diagnosis can be difficult and this entity should be suspected in patients with high free tiroxine (T4) concentrations, low or suppressed thyroglobulin concentrations, normal urinary iodide excretion and low or suppressed (131)I uptake. To establish the differential diagnosis, thyrotoxicosis factitia must be distinguished from several diseases with low (131)I uptake, such as Graves' disease, subacute thyroiditis, hyperthyroidism due to excessive iodine intake, struma ovarii and metastasis from thyroid cancer. Treatment is based on b-blockers to reduce symptoms and avoid iatrogeny. We present a case of thyrotoxicosis factitia treated in our outpatient clinic.

Thyrotoxicosis revealing metastases of unrecognized thyroid cancer: a report on two cases

We report two cases of thyrotoxicosis-revealing functional metastases of a follicular carcinoma that extended to the bones, liver and kidneys in one case and to the lungs in the other. Both patients had undergone surgical intervention for a thyroid nodule more than 15 years before the diagnosis of thyrotoxicosis and metastatic dissemination. In both the cases, the carcinoma was not recognized by the pathologist after the first surgical intervention, but was finally diagnosed several years later due to the occurrence of thyrotoxicosis. Iodine-131 therapy was effective at suppressing the thyrotoxicosis in both the patients. The effectiveness on the metastatic extension was very different for each patient: in the first case, the patient died a few years later without any control of the metastatic tissue. For the second patient, the metastases disappeared a few months after radioiodine treatment, with the patient still in remission more than 10 years later. The physiopathology and the evolution of these two cases are discussed with the data available in the literature.

Multifocal hyperfunctioning thyroid carcinoma without metastases

Hyperthyroidism due to thyroid carcinoma is rare, and most cases are caused by hyperfunctioning metastatic thyroid carcinoma rather than primary carcinoma. Among primary hyperfunctioning thyroid carcinoma, multifocal thyroid carcinoma is exceedingly rare, with the only one case being reported in the literature. Here, we describe the case of a 62-year-old woman with multifocal functioning thyroid carcinoma. Technetium-99m (99m Tc) scintigraphic imaging showed four hot areas in the thyroid gland. Histopathological examination of all four nodules revealed papillary carcinoma, corresponding to hot areas in the 99m Tc scintigram. DNA sequencing of the thyrotropin receptor (TSH-R) gene from all nodules revealed no mutation, indicating that activation of TSH-R was unlikely in the pathophysiogenesis of hyperfunctioning thyroid carcinoma in the present case.

[A case of hyperthyroidism due to functioning metastasis of differentiated thyroid carcinoma. Discussion and literature review]

We report on a very rare case of hyperthyroidism due to multiple autonomously functioning bone metastasis of papillary thyroid cancer in a 79-year-old woman. This situation remains extremely uncommon, as shown by our review of the literature; only 47 similar cases have been published from 1946 to 2005. The pathogenic mechanism remains largely unknown in spite of several hypotheses (conjunction in volume and differentiation, auto-antibodies). Hyperthyroidism can be severe, and often T3 levels are markedly more elevated than T4 levels. Apart from hyperthyroidism caused by the hormone-production, clinical features are similar to that of usual metastatic thyroid cancer, occurring in elderly women in most cases, and of follicular type on pathology. Metastases mostly occur in bones and lungs. Treatment relies mainly on radio-iodine ((131)I), which is efficient on hormonal disorders, and prognosis appears to be correlated with the ability of the metastatic sites to concentrate radio-iodine.

Differentiated thyroid cancer presenting with thyrotoxicosis due to functioning metastases

Thyrotoxicosis due to functioning metastases in differentiated thyroid cancer (DTC) is exceedingly rare. We report a case of follicular carcinoma in a 54-year-old manager, who presented with thyrotoxicosis, shortness of breath and lung metastases. Transbronchial biopsy of a pulmonary nodule demonstrated normal thyroid. This was interpreted as representing very well-differentiated thyroid cancer. CT, (131)I whole-body imaging and dosimetry is described following total thyroidectomy and repeated radioiodine administration (cumulative activity 34.6 GBq). The patient became asymptomatic with almost complete eradication of the pulmonary metastases. Potential complications of thyroid storm, bone marrow failure and pulmonary fibrosis following radioiodine are discussed, together with methods to minimise these risks.

Amiodarone-induced hyperthyroidism in a patient with functioning papillary carcinoma of the thyroid and extensive hepatic metastases

Thyroid hormone producing thyroid carcinoma is an uncommon cause of thyrotoxicosis. A patient with extensive hepatic metastases from well-differentiated carcinoma is presented. Administration of amiodarone for atrial fibrillation led to the development of hyperthyroidism. Precipitation of thyrotoxicosis by iodine-containing compounds in patients with thyroid carcinoma is rare. The relatively high iodine load and the slow elimination of amiodarone complicate the clinical management of such patients.

Papillary thyroid carcinoma without metastases manifesting as an autonomously functioning thyroid nodule

A 59-year-old woman with papillary thyroid carcinoma inside of an autonomously functioning thyroid nodule is described in this report. The patient was referred to our clinic because of rapid weight loss and swelling on the left side of the neck. Ultrasonography of the thyroid demonstrated a nonhomogeneous nodule in the lower part of an enlarged left lobe. Both 99mTc and 123I thyroid scintigraphic imaging showed a hot area corresponding to the nodule with lower uptake in the remaining thyroid tissue. Histopathological examination of the nodule revealed papillary adenocarcinoma, and the immunohistochemistry proved weak but positive staining for triiodothyronine and thyroxine. Based on these findings, the nodule was diagnosed as a functioning papillary adenocarcinoma. Although thyroid carcinoma manifesting as a hot nodule on the radionuclide isotope scan is an extremely rare occurrence, the current case is clinically important because it suggests that the diagnosis of a hot nodule cannot always rule out thyroid carcinoma in the nodule, and that even a hot nodule requires careful management so that the malignancy is not overlooked.

Thyrotoxicosis due to metastatic papillary thyroid cancer in a patient with Graves' disease

Thyrotoxicosis resulting from functional thyroid cancer metastases is extremely rare, and is mostly caused by follicular cancer. The lesions causing thyrotoxicosis are usually bulky and extensive. We report here a patient with Graves' disease and concomitant papillary thyroid cancer who developed metastases causing symptomatic thyrotoxicosis. His serum titers of thyroid stimulating Ig (TSIs) were elevated. We believe that TSIs were responsible for thyrotoxicosis by stimulating hormonogenesis in the metastatic lesions.

Severe thyrotoxicosis induced by thyroid metastasis of lung adenocarcinoma: a case report and review of the literature

A 50-year-old woman who had undergone lung lobectomy because of lung adenocarcinoma presented with thyrotoxicosis, neck swelling, and cervical lymphadenopathy one month after the operation. The total serum triiodothyronine (T3) and thyroxine (T4) levels were markedly elevated to 514 ng/dL and 26.4 microg/dL, respectively, and serum thyrotropin (TSH) was suppressed to less than 0.005 microU/mL. Although the thyroid gland had been normal before surgery, chest computed tomography (CT) scan revealed a markedly enlarged thyroid gland only 1 month after surgery. 123I uptake for 24 hours was suppressed to 4% in the thyroid gland with no uptake elsewhere including the lung. Fine-needle aspiration cytology (FNAC) of the thyroid showed invasion of poorly differentiated adenocarcinoma cells, cytologically identical to the cells obtained from sputum and those infiltrating the resected sections of the lung adenocarcinoma. Immunohistochemical studies of resected lung tissues did not show positive staining for thyroglobulin, carcinoembryonic antigen (CEA), or surfactant protein A. Clinically, the thyrotoxicosis had spontaneously improved, followed by a hypothyroid state with shrinkage of the thyroid gland after chemotherapy. Despite repeated chemotherapy and the administration of thyroxine for hypothyroidism, the patient died of respiratory failure 9 months after the onset of thyrotoxicosis. From these findings and the clinical course, thyroid metastasis, developing subacutely from lung adenocarcinoma, was diagnosed. We speculate that aggressive invasion of tumor cells into the thyroid gland resulted in highly destructive thyrotoxicosis.

Syndromes of thyrotoxicosis with low radioactive iodine uptake

It is very important to diagnose correctly the etiology of thyrotoxicosis, because the course and treatment of thyrotoxicosis with low radioactive iodine uptake differ significantly from that of hyperthyroidism due to Graves' disease or toxic nodular goiter. Many causes of subacute thyroiditis have been identified producing a characteristic course of transient hyperthyroidism, followed by hypothyroidism, and usually recovery. Ectopic hyperthyroidism includes factitious thyroid hormone ingestion, struma ovarii, and, rarely, large deposits of functioning thyroid cancer metastases. Iodine-induced hyperthyroidism may be associated with low radioiodine uptakes. Amiodarone-associated hyperthyroidism may be the result of subacute thyroiditis or iodine-induced hyperthyroidism; assessment and treatment can be quite challenging.

Development of primary hypothyroidism with antithyroglobulin, antiperoxidase, and blocking-type thyrotropin receptor antibodies after radiation therapy for neuroblastoma

We describe a girl with hypothyroidism and blocking-type thyrotropin receptor antibodies that developed after chemotherapy and irradiation of the neck region for neuroblastoma. Results of thyroid studies before treatment were normal. Twenty months after completion of treatment, the girl had hypothyroidism with high titers of blocking-type thyrotropin receptor antibodies, antithyroglobulin, and antiperoxidase antibodies.

Thyroid hormone-producing metastases in differentiated thyroid cancer

Thyroid hormone production by metastases of differentiated thyroid carcinoma is very rare and its pathogenesis is still unknown. The aim of this study was to present some clinical and demographic evidence that thyroid hormone-producing metastases of differentiated thyroid carcinoma are related to environmental factors, probably iodine deficiency. A cross-sectional study was performed on thirty-five patients with distant metastases, identified in a group of 125 patients with differentiated thyroid carcinoma previously submitted to total or near total thyroidectomy. In 6 patients (5 females, 1 male; age range, 50 to 64 yr) we had evidence that the metastases were actively producing thyroid hormones and in 29 patients (21 females, 8 males; age range 8 to 84 yr) the metastases were considered to be nonthyroid hormone-producing. Serum levels of T3, T4, and thyroglobulin were measured by RIA, TSH by IRMA, and 131I whole-body scintigraphy was performed 72 h after 187 Mbq of 131I. All patients with metastases producing thyroid hormones presented a pure follicular thyroid carcinoma. They also differed from patients with nonproducing metastases in the frequent presence of goiter of long duration as the first clinical manifestation of thyroid disease (p < 0.01), and a higher proportion of patients coming from an iodine deficient area (5/6 vs. 6/29, p < 0.05). In these patients the serum thyroglobulin levels tended to be higher (p = 0.069) as compared with the nonproducing metastases group. In conclusion, a late diagnosis of follicular carcinoma in patients with long-standing multinodular goiter allowed the development of well differentiated and bulky metastases retaining the ability to produce thyroid hormones.