Diagnosis and management of amiodarone-induced thyrotoxicosis: similarities and differences between North American and European thyroidologists

Cardiac evaluation in amiodarone-induced thyroid dysfunction with suspected cardiac ischemia?: a case report and review of the literature

BACKGROUND

Amiodarone-induced thyroid dysfunction (AIT) is a side-effect associated with the use of Amiodarone for the treatment of refractory arrythmias. Resulting hyperthyroidism can precipitate cardiac complications, including cardiac ischemia and myocardial infarction, although this has only been described in a few case reports.

CASE PRESENTATION

We present here a clinical scenario involving a 66-year-old male Caucasian patient under Amiodarone for atrial fibrillation, who developed AIT. In the presence of dyspnea, multiple cardiovascular risk factors and ECG abnormalities, a transthoracic echocardiogram was performed, showing inferobasal hypokinesia. This led to further investigations through a cardiac PET-CT, where cardiac ischemia was suspected. Ultimately, the coronary angiography revealed no abnormalities. Nonetheless, these extensive cardiologic investigations led to a delay in initiating an emergency endovascular revascularization for acute-on-chronic left limb ischemia. Although initial treatment using Carbimazole was not successful after three weeks, the patient reached euthyroidism after completion of the treatment with Prednisone so that eventually thyroidectomy was not performed. Endovascular revascularization was finally performed after more than one month.

CONCLUSIONS

We discuss here cardiac abnormalities in patients with AIT, which may be due to relative ischemia secondary to increased metabolic demand during hyperthyroidism. Improvement of cardiac complications is expected through an optimal AIT therapy including medical therapy as the primary approach and, when necessary, thyroidectomy. Cardiac investigations in the context of AIT should be carefully considered and may not justify delaying other crucial interventions. If considered mandatory, diagnostic procedures such as coronary angiography should be preferred to functional testing.

Short review: novel concepts in the approach to patients with amiodarone-induced thyrotoxicosis

INTRODUCTION

Amiodarone-induced thyrotoxicosis is associated with high morbidity and mortality rates. The approach to this condition is widely variable across different medical specialists and even among expert endocrinologists. As a matter of fact, the approach to amiodarone-induced thyrotoxicosis has always been considered difficult, due to diagnostic uncertainties easily resulting in missteps, and therapeutic challenges easily resulting in unresponsiveness or slow-responsiveness to the administered drugs.

PURPOSE

Our purpose is to review novelties emerged during the last years about this condition, with the aim to provide novel insights on the diagnostic and therapeutic management of this challenging condition.

Perchlorates in the treatment of hyperthyroidism and thyrotoxicosis: a comprehensive review

INTRODUCTION

Perchlorates are ionic inhibitors antagonizing iodine transport into thyrocytes, hampering thyroid hormone synthesis. Nevertheless, perchlorates are not considered as first-line treatment in hyperthyroidism and thyrotoxicosis as compared to other pharmacological and non-pharmacological interventions.

AIM

Reassessing the therapeutic role of perchlorates in hyperthyroidism and thyrotoxicosis throughout a systematic review of the Literature.

METHODS

Guidelines were searched and examined to summarize current recommendations on the use of perchlorates in the management of hyperthyroidism. Randomized and non-randomized clinical trials were also searched and reviewed to summarize the efficacy/effectiveness and safety of perchlorates in hyperthyroidisms and thyrotoxicosis.

RESULTS

The management of specific forms of hyperthyroidism was considered, including Graves' disease (GD) in non-pregnant adults, hyperthyroidisms in pregnancy, iodine media contrast-induced hyperthyroidism, amiodarone-induced hyperthyroidisms, and thyroid storm. Most of the reported studies had remarkable limitations in terms of study design (non-controlled trials, lack of blinding), low number of participants, and the lack of clinically relevant endpoints, such as cardiovascular events, cardiovascular mortality, and teratogenicity. Overall, perchlorates could be considered a second-line treatment after thionamides, radioiodine, and total thyroidectomy in both GD and hyperthyroidisms in pregnancy. The therapeutic potential of perchlorates alone or in combination with other agents could be considered a second-line treatment of iodine-related hyperthyroidisms and thyroid storm.

CONCLUSION

Despite the low level of evidence, perchlorates could be considered in such specific forms of thyroid disorders, including iodine-induced hyperthyroidism and thyroid storm.

Amiodarone-Induced Myxedema Coma in Elderly Patients: A Systematic Review of Case Reports

This systematic review aimed to explore whether elderly patients administered amiodarone were susceptible to developing myxedema coma. Utilizing the Cochrane guidelines, a comprehensive review of databases such as Medline (PubMed), Science Direct, CINAHL Cochrane, and Google Scholar was undertaken to examine case reports on amiodarone-induced myxedema coma. Following stringent criteria for inclusion, 12 pertinent case reports were identified. These findings suggested a high probability of myxedema coma development in patients who had been administered amiodarone. Specifically, patients who received an oral dosage of 100-200 mg of amiodarone were reported to have developed bradycardia and hypothermia alongside elevated thyroid-stimulating hormone (TSH) levels. Upon diagnosis, the majority of patients were treated with a regimen of levothyroxine and hydrocortisone medication. Despite the myriad potential causes of myxedema coma complicating the diagnosis, it was found that through a combination of clinical symptoms and serum TSH measurements, a confirmed diagnosis could be reached. Furthermore, it was observed that amiodarone-induced myxedema coma responded favorably to treatment with levothyroxine and glucocorticoids.

Real-life data on the impact of medical therapy for amiodarone-induced thyrotoxicosis on CV events and hospitalizations

CONTEXT

Patients with amiodarone-induced thyrotoxicosis (AIT) often receive the initial therapy for thyrotoxicosis in several different medical settings before admission to a referral center. Whether the first-line medical therapy (i.e. therapies for thyrotoxicosis at first diagnosis of AIT) affects the outcome of AIT patients is unknown.

STUDY DESIGN

Single-center historical-prospective cohort study of 313 AIT patients.

METHODS

Clinical and biochemical data were collected at first diagnosis, at a referral center, and during the course of AIT. Primary outcomes were cardiovascular events and hospitalizations. First-line therapies were considered appropriate when they included glucocorticoids for type 2 AIT and methimazole for type 1 AIT at the approved dosage, either alone (optimal medical therapy, OMT) or in combination (right-dose combination therapy, RCT). Other therapies were considered not appropriate, including no therapy. Duration of exposure to thyrotoxicosis was the time from first diagnosis of AIT to its remission.

RESULTS

34.5% patients received appropriate therapies (28.1% OMT, 6.4% RCT), whereas the remaining (65.5%) received non-appropriate therapies. Cardiovascular events, and hospitalizations were more frequent in patients who received non-appropriate therapies (33.2% vs 4.5%, and 24.9% vs 6.5%, respectively; p<0.0001 for both). Appropriate therapies reduced serum thyroid hormone concentrations (p=0.018) from first diagnosis to referral, unlike the non-appropriate therapies. The duration of exposure to thyrotoxicosis was longer in patients receiving non-appropriate therapies and was a risk factor for arrhythmias (HR 1.004, p=0.0008), MACEs (HR 1.004, p=0.020) and hospitalizations (HR 1.006, p<.0001).

CONCLUSIONS

The first medical therapy of AIT influences the exposure time to thyrotoxicosis and the occurrence of cardiovascular events and hospitalizations.

Clinical Review and Update on the Management of Thyroid Storm

Thyroid storm is a severe manifestation of thyrotoxicosis. Thyroid storm is diagnosed as a combination of thyroid function studies showing low to undetectable thyroid stimulating hormone (TSH) (<0.01mU/L) with elevated free thyroxine (T4) and/or triiodothyronine (T3), positive thyroid receptor antibody (TRab) (if Graves' disease is the underlying etiology), and with clinical signs and symptoms of end organ damage. Treatment involves bridging to a euthyroid state prior to total thyroidectomy or radioactive iodine ablation to limit surgical complications such as excessive bleeding from highly vascular hyperthyroid tissue or exacerbation of thyrotoxicosis. The purpose of this article is a clinical review of the various treatments and methodologies to achieve a euthyroid state in patients with thyroid storm prior to definitive therapy.

Optimization of premedication of patients with arterial hypertension and severe ventricular rhythm disturbances with Amiodarone-associated thyrotoxicosis

Introduction: The effectiveness of premedication of patients with arterial hypertension and severe ventricular rhythm disturbances against the background of Amiodarone-associated thyrotoxicosis, high anxiety and cyclothymiae disorders should be based on the pharmacological positions of the need to reduce the risk of dangerous adverse cardiovascular reactions.

Materials and methods: During the research, a clinical group of 114 patients with arterial hypertension, severe ventricular arrhythmias and Amiodarone-associated type I thyrotoxicosis was formed: four subgroups were identified. In Subgroup 1 (n=22), no premedication was given. In Subgroup 2 (n=32), premedication was given with Diazepam and magnesium sulfate in a prolonged mode. In Subgroup 3 (n=30), the patients received Diazepam the day before surgery. In Subgroup 4 (n=30), premedication was given with Midazolam. A dynamic assessment of the severity of anxiety, depression, sedation and daily monitoring of blood pressure and ECG were carried out.

Results and discussion: After surgery, in Subgroup 1, the level of anxiety and depression increased. In all other Subgroups, regardless of the type of premedication, the use of benzodiazepines was accompanied by a decrease in the level of anxiety after surgery. A decrease in pressure load and an increase in the stability of the parameters of systemic hemodynamics were registered in Subgroup 2 of patients, whereas in Subgroup 4 of patients, the pressure load increased while limiting the differences in blood pressure values during the day. After surgery, in Subgroup 2, cardiac rhythm disturbances were less common; in Subgroup 3, the structure of rhythmogenesis disturbances in the heart almost did not change, and in Subgroup 4, there was an unfavorable trend of an increase in the frequency of supraventricular, single and group ventricular extrasystoles.

Conclusion: The prolonged premedication with long-acting benzodiazepines and magnesium preparations in patients with arterial hypertension, ventricular rhythm disturbances against the background of Amiodarone-associated thyrotoxicosis reduces the level of anxiety, as well as the risk of developing cardiovascular complications and instability of systemic hemodynamics.

Update on diagnosis and treatment of hyperthyroidism: ultrasonography and functional imaging

Ultrasonography and radionuclide imaging using [^99mTc]Pertechnetate or radioactive iodine isotopes are essential tools used during the diagnostic workup of hyperthyroidism with or without structural alterations of the thyroid. Color duplex sonography and ultrasound elastography may add important information to find the cause of the hormone excess. During the last few years, hybrid imaging using SPECT/-(CT) or PET-based methods, such as [¹²⁴]Iodine-PET/CT or [¹²⁴]Iodine-PET/ultrasound have been increasingly used, playing a role in the context of localizing ectopic thyroid tissue or in multinodular goiter. Recently, promising data has been published on the use of [^99mTc]MIBI imaging in amiodarone induced hyperthyroidism.

Increased Risk of Antithyroid Drug Agranulocytosis Associated with Amiodarone-Induced Thyrotoxicosis: A Population-Based Cohort Study

BACKGROUND

Agranulocytosis occurs in 0.2-0.5% of patients treated with the antithyroid drugs (ATDs) methimazole and propylthiouracil. The objectives of this study were to evaluate the risk of ATD-related agranulocytosis in patients with amiodarone-induced thyrotoxicosis (AIT), and to compare it with the agranulocytosis risk in patients with thyrotoxicosis due to other etiologies treated with ATDs.

METHODS

This was a retrospective cohort study. Participants were 14,781 adult patients with thyrotoxicosis, newly treated with an ATD between January 1, 2002, and December 31, 2015. Among them were 593 patients treated by ATDs due to AIT. The main outcome measures were incidence rates and crude and adjusted hazard ratios using univariate and multivariable Cox regression models for ATD-related agranulocytosis within one year of treatment initiation, in association with AIT.

RESULTS

Agranulocytosis occurred in 28 (0.19%) of patients newly treated with methimazole or propylthiouracil during the first year of follow-up. Of these 28 patients, 8/593 (1.35%) were AIT patients and 20/14,188 (0.14%) were thyrotoxic patients that was not AIT related (p < 0.001). Incidence rates were 22 (9.47-43.36) cases/1000 person-years of follow-up in AIT, and 1.79 (1.09-2.76)/1000 person-years of follow-up in non-AIT thyrotoxicosis (p < 0.0001). In univariate Cox regression analysis, risk for ATD agranulocytosis associated with AIT was 9.71 (4.28-22.05) compared to the risk in non-AIT thyrotoxicosis. In a multivariable model, adjusting for age, sex, body mass index, smoking history, year of cohort entry, diabetes mellitus, hypertension, renal failure, beta blockers, calcium channel blockers, anti-aggregants, and dose of ATDs, the risk associated with AIT was 5.70 (2.14-15.21). In a model adjusted for a propensity score to receive amiodarone, risk for ATD agranulocytosis associated with AIT was 6.32 (1.22-32.70).

CONCLUSIONS

ATD use is associated with a higher risk for agranulocytosis in patients with AIT.

Diagnosis and Clinical Course of Three Adolescents with Amiodarone-Induced Hyperthyroidism

Amiodarone-induced hyperthyroidism is a known side effect of amiodarone treatment. In the pediatric population, long-term amiodarone treatment is rarely indicated because of its severe side effects including thyroid function impairment. Treatment is therefore restricted to therapy-resistant arrhythmias. In the literature, scarce data are available on the management and therapy of amiodarone-induced thyroid dysfunction at a young age. We present three adolescent patients developing amiodarone-induced thyrotoxicosis in the months after amiodarone therapy. A latency period for thyroid dysfunction has been described in adulthood but was not previously reported in pediatric patients. The gap between amiodarone treatment and the development of symptoms and the diagnosis of hyperthyroidism was between 3 and 10 months. In two patients, hyperthyroidism was transient and resolved without treatment. These two patients, one boy and on girl, were almost asymptomatic. In contrast, in one male patient overt and severe hyperthyroidism developed. We began treatment with thiamazole without benefit. Control of hyperthyroidism was achieved under prednisone treatment, which was continued for 9 months. Clinical evaluation proved an amiodarone-induced destructive thyroiditis in this patient. Amiodarone-induced thyroid dysfunction is frequent also in pediatric patients with long-term amiodarone treatment. Patients and clinicians should be aware of the impact of amiodarone on thyroid function during and also in the months and maybe years after treatment. Careful follow-up is needed, as symptoms might be associated with the underlying cardiac disease in these patients. Amiodarone-induced thyrotoxicosis often resolves without treatment but can be challenging in some cases.

[Challenges in the management of amiodarone-induced thyrotoxicosis]

Amiodarone, a benzofuranic iodine-rich pan antiarrhythmic drug, is frequently associated with thyroid dysfunction. This side effect is heterogeneous and unpredicted, motivating regular evaluation of thyroid function tests. In contrary to hypothyroidism, amiodarone-induced thyrotoxicosis (AIT) is a challenging situation owing to the risk of deterioration of the general and cardiac status of such debilitating patients. Classically, AIT is either an iodine-induced thyrotoxicosis in patients with an abnormal thyroid (type I), or due to a subacute thyroiditis on a "healthy" thyroid (type II). Even if many studies tried to better identify the types of AIT, the diagnostic dilemma of type of AIT could be present, and many patients are treated by an association of antithyroid drugs (useful for type I AIT) with corticoids (useful for type II AIT). Being the main etiological factor in AIT, amiodarone is supposed to be stopped, but it could remain the only anti-arrhythmic option that is needed to be either continued or reintroduced to improve the cardiovascular survival. Recently, many studies demonstrated that amiodarone could be continued or reintroduced in patients with history of type II AIT. Nevertheless, in the other patients, amiodarone maintenance complicates the therapeutic response to the antithyroid drugs and increases the risk of AIT recurrence. Thus, amiodarone therapy is preferred to be interrupted. In such patients, thyroid ablation is recommended once AIT is under control.

Issues in amiodarone-induced thyrotoxicosis: Update and review of the literature

Amiodarone, a benzofuranic iodine-rich pan-anti-arrhythmic drug, induces amiodarone-induced thyrotoxicosis (AIT) in 7-15% of patients. AIT is a major issue due to its typical severity and resistance to anti-thyroid measures, and to its negative impact on cardiac status. Classically, AIT is either an iodine-induced thyrotoxicosis in patients with abnormal thyroid (type 1), or due to acute thyroiditis in a "healthy" thyroid (type 2). Determination of the type of AIT is a diagnostic dilemma, as characteristics of both types may be present in some patients. As it is the main etiological factor in AIT, it is recommended that amiodarone treatment should be stopped; however, it may be the only anti-arrhythmic option, needing to be either continued or re-introduced to improve cardiovascular survival. Recently, a few studies demonstrated that amiodarone could be continued or re-introduced in patients with history of type-2 AIT. However, in the other patients, it is recommended that amiodarone treatment be interrupted, to improve response to thioamides and to alleviate the risk of AIT recurrence. In such patients, thyroidectomy is recommended once AIT is under control, allowing safe re-introduction of amiodarone.

2018 European Thyroid Association (ETA) Guidelines for the Management of Amiodarone-Associated Thyroid Dysfunction

Treatment with amiodarone is associated with changes in thyroid function tests, but also with thyroid dysfunction (amiodarone-induced hypothyroidism, AIH, and amiodarone-induced thyrotoxicosis, AIT). Both AIH and AIT may develop in apparently normal thyroid glands or in the presence of underlying thyroid abnormalities. AIH does not require amiodarone withdrawal, and is treated with levothyroxine replacement if overt, whereas subclinical forms may be followed without treatment. Two main types of AIT are recognized: type 1 AIT (AIT 1), a form of iodine-induced hyperthyroidism occurring in nodular goitres or latent Graves disease, and type 2 AIT (AIT 2), resulting from destructive thyroiditis in a normal thyroid gland. Mixed/indefinite forms exist due to both pathogenic mechanisms. AIT 1 is best treated with thionamides that may be combined for a few weeks with sodium perchlorate to make the thyroid gland more sensitive to thionamides. AIT 2 is treated with oral glucocorticoids. Once euthyroidism has been restored, AIT 2 patients are followed up without treatment, whereas AIT 1 patients should be treated with thyroidectomy or radioiodine. Mixed/indefinite forms of AIT are treated with thionamides. Oral glucocorticoids can be added from the beginning if a precise diagnosis is uncertain, or after a few weeks if response to thionamides alone is poor. The decision to continue or to stop amiodarone in AIT should be individualized in relation to cardiovascular risk stratification and taken jointly by specialist cardiologists and endocrinologists. In the presence of rapidly deteriorating cardiac conditions, emergency thyroidectomy may be required for all forms of AIT.

Nonthionamide Drugs for the Treatment of Hyperthyroidism: From Present to Future

Hyperthyroidism is a common endocrine disease. Although thionamide antithyroid drugs are the cornerstone of hyperthyroidism treatment, some patients cannot tolerate this drug class because of its serious side effects including agranulocytosis, hepatotoxicity, and vasculitis. Therefore, nonthionamide antithyroid drugs (NTADs) still have an important role in controlling hyperthyroidism in clinical practice. Furthermore, some situations such as thyroid storm or preoperative preparation require a rapid decrease in thyroid hormone by combination treatment with multiple classes of antithyroid drugs. NTADs include iodine-containing compounds, lithium carbonate, perchlorate, glucocorticoid, and cholestyramine. In this narrative review, we summarize the mechanisms of action, indications, dosages, and side effects of currently used NTADs for the treatment of hyperthyroidism. In addition, we also describe the state-of-the-art in future drugs under development including rituximab, small-molecule ligands (SMLs), and monoclonal antibodies with a thyroid-stimulating hormone receptor (TSHR) antagonist effect.

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Zusammenfassung. Amiodaron-induzierte Schilddrüsenfunktionsstörungen (Hypo- und Hyperthyreosen) sind häufig (14–18 % der behandelten Patienten). Oft werden sie spät erkannt und ungenügend behandelt. Eine ausführliche Anamnese und klinische Untersuchung kann Risikopatienten identifizieren. Die Hyperthyreose ist klinisch oft schwierig zu diagnostizieren, da Amiodaron beta-blockierende Aktivitäten aufweist und so die adrenergenen Symptome der Schilddrüsenüberfunktion maskiert. Regelmässige Laborkontrollen sind unerlässlich. Dabei gilt es zu berücksichtigen, dass Amiodaron den Schilddrüsenhormon-Metabolismus und damit die Schilddrüsenwerte beeinflusst. Während die Therapie der Hypothyreose einfach ist (Substitution), ist die Hyperthyreose oft schwieriger und langwieriger in der Behandlung (Thyreostatika, Kortikosteroide, gelegentlich Perchlorat oder sogar eine totale Thyroidektomie). Obwohl die Bedeutung des Amiodarons in der Behandlung der Rhythmusstörungen wegen neuerer Therapiestrategien abnimmt, ist die Kenntnis der potenziellen Nebenwirkungen (nicht nur der endokrinologischen) nach wie vor wichtig.

Diagnosis and Management of Noncardiac Complications in Adults With Congenital Heart Disease: A Scientific Statement From the American Heart Association

Life expectancy and quality of life for those born with congenital heart disease (CHD) have greatly improved over the past 3 decades. While representing a great advance for these patients, who have been able to move from childhood to successful adult lives in increasing numbers, this development has resulted in an epidemiological shift and a generation of patients who are at risk of developing chronic multisystem disease in adulthood. Noncardiac complications significantly contribute to the morbidity and mortality of adults with CHD. Reduced survival has been documented in patients with CHD with renal dysfunction, restrictive lung disease, anemia, and cirrhosis. Furthermore, as this population ages, atherosclerotic cardiovascular disease and its risk factors are becoming increasingly prevalent. Disorders of psychosocial and cognitive development are key factors affecting the quality of life of these individuals. It is incumbent on physicians who care for patients with CHD to be mindful of the effects that disease of organs other than the heart may have on the well-being of adults with CHD. Further research is needed to understand how these noncardiac complications may affect the long-term outcome in these patients and what modifiable factors can be targeted for preventive intervention.

The clinical value of regular thyroid function tests during amiodarone treatment

OBJECTIVE

Amiodarone is used for the maintenance of sinus rhythm in patients with arrhythmias, but thyroid dysfunction (amiodarone-induced thyrotoxicosis (AIT) or amiodarone-induced hypothyroidism (AIH)) is a common adverse effect. As the onset of AIT and AIH may be unpredictable, the value of long-term regular monitoring of amiodarone treated patients for thyroid dysfunction is still uncertain.

DESIGN

We retrospectively documented the frequency at which overt thyroid dysfunction was preceded by subclinical thyroid dysfunction.

METHODS

We included 303 patients treated with amiodarone between 1984 and 2007. AIT was defined as a lowered TSH level with an elevated free thyroxine (FT4) and AIH was defined as an elevated TSH level with a decreased or subnormal FT4. Subclinical AIT was defined as a lowered TSH level with a normal FT4 and subclinical AIH as an elevated TSH level with a normal FT4.

RESULTS

200 men and 103 women, aged 62 ± 12.0 years, suffering from atrial (260) or ventricular (43) arrhythmias, were evaluated. During a median follow-up of 2.8 (1.0-25) years, 44 patients developed AIT and 33 AIH. In 42 (55%) patients who developed AIT/AIH, earlier thyroid function tests showed no subclinical AIT or subclinical AIH. In 35 (45%) patients, AIT/AIH was preceded by subclinical AIT or subclinical AIH (16/44 for AIT and 19/33 for AIH).

CONCLUSIONS

In a considerable proportion of patients who developed AIT/AIH, earlier thyroid function tests showed no subclinical AIT/AIH. Less than half of the patients with a subclinical event subsequently developed overt AIT/AIH. This study provides data to reconsider the yield of regular testing of thyroid function to predict overt thyroid dysfunction in amiodarone treated patients.

Successful Pretreatment Using Plasma Exchange before Thyroidectomy in a Patient with Amiodarone-Induced Thyrotoxicosis

INTRODUCTION

Amiodarone, used for the management of tachyarrhythmias, is associated with both hypothyroidism and thyrotoxicosis. Total thyroidectomy is an effective procedure for promptly reducing circulating thyroid hormone levels. It has been proposed in patients who have severe amiodarone-induced thyrotoxicosis (AIT) or are refractory to medical therapy, or when such therapy is contraindicated. Therapeutic plasma exchange (TPE) may be considered as a pretreatment for restoring a euthyroid state preoperatively, thereby reducing a patient's symptoms and the potential perioperative risk associated with thyrotoxicosis.

CASE REPORT

We describe the case of a 62-year-old man with type 2 AIT who presented with severe unremitting thyrotoxicosis after 8 weeks of medical therapy with glucocorticosteroids, thiamazole, and potassium perchlorate. Given the severity of his presentation, a total thyroidectomy was indicated. TPE was performed preoperatively and was successful in rapidly restoring euthyroidism. This dramatically improved the patient's symptoms which had been suggestive of ischemic heart disease. Subsequently, the patient underwent total thyroidectomy under general anesthesia without any major complications.

CONCLUSION

TPE is successful in rapidly restoring a clinical and biochemical euthyroid state, and may be used to decrease the perioperative risks associated with thyroidectomy in patients with life-threatening thyrotoxicosis or in cases refractory to medical treatment.

Evaluation of 99mTc-MIBI in thyroid gland imaging for the diagnosis of amiodarone-induced thyrotoxicosis

OBJECTIVE

Amiodarone-induced thyrotoxicosis (AIT) is caused by amiodarone as a side effect of cardiovascular disease treatment. Based on the differences in their pathological and physiological mechanisms, many methods have been developed so far to differentiate AIT subtypes such as colour flow Doppler sonography (CFDS) and 24-h radioiodine uptake (RAIU). However, these methods suffer from inadequate accuracy in distinguishing different types of AITs and sometimes lead to misdiagnosis and delayed treatments. Therefore, there is an unmet demand for an efficient method for accurate classification of AIT.

METHODS

Technetium-99 methoxyisobutylisonitrile (^99mTc-MIBI) thyroid imaging was performed on 15 patients for AIT classification, and the results were compared with other conventional methods such as CFDS, RAIU and ^99mTcO₄ imaging.

RESULTS

High uptake and retention of MIBI in thyroid tissue is characteristic in Type I AIT, while in sharp contrast, low uptake of MIBI in the thyroid tissue was observed in Type II AIT. Mixed-type AIT shows uptake value between Types I and II. MIBI imaging outperforms other methods with a lower misdiagnosis rate.

CONCLUSION

Among the methods evaluated, MIBI imaging enables an accurate identification of Type I, II and mixed-type AITs by showing distinct images for different types of AITs. The results obtained from our selected subjects revealed that MIBI imaging is a reliable method for diagnosis and classification of AITs and MIBI imaging has potential in the treatment of thyroid diseases. Advances in knowledge: ^99mTc-MIBI imaging is a useful method for the diagnosis of AIT. It can distinguish different types of AITs especially for mixed-type AIT, which is usually difficult to treat. ^99mTc-MIBI has potential advantages over conventional methods in the efficient treatment of AIT.

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.

Amiodarone-induced thyrotoxicosis in adults with congenital heart disease--clinical presentation and response to therapy

OBJECTIVE

The development of amiodarone-induced thyrotoxicosis (AIT) can threaten the hemodynamic stability of adult patients with congenital heart disease (CHD). Here, we describe the natural history and treatment response of AIT in this at-risk population.

METHODS

We studied retrospectively all cases of AIT that occurred in CHD patients at our institution after a minimum of 3 months on amiodarone. Subjects were identified from the cohort of adults with CHD who were treated at the Mayo Clinic Adult CHD clinic between 1987 and 2009.

RESULTS

We identified 23 cases of AIT: 7 were type 1, 13 were type 2, and 3 were undefined due to insufficient data. Most patients were symptomatic (17 of 23, 74%), with arrhythmia and weight loss as the most common symptoms. The majority (12 of 23, 52%) were initially observed; 10 patients (43%) were treated medically and 1 patient (5%) underwent thyroidectomy. Four patients from the observation group eventually required active treatment and 3 patients from the medical group required surgery. Asymptomatic patients tended to resolve under observation (5 of 7, 71.4%) rather than progress to active treatment (0 of 4) (P = .06). Discontinuation of amiodarone, AIT type, or use of perchlorate did not impact AIT duration.

CONCLUSION

AIT in CHD patients exhibits a wide range of severity and sensitivity to medical therapy. Asymptomatic patients display a trend toward AIT resolution with observation alone. Amiodarone continuation does not appear to impact management outcome or disease duration. Additional studies in this high-risk population could identify elements of pathophysiology that would point toward better disease prevention and treatment.

The presence of anti-thyroglobulin (TgAb) and/or anti-thyroperoxidase antibodies (TPOAb) does not exclude the diagnosis of type 2 amiodarone-induced thyrotoxicosis

PURPOSE

It is widely accepted that type 2 amiodarone-induced thyrotoxicosis (AIT) generally occurs in patients with a normal thyroid gland without signs of thyroid autoimmunity. However, it is currently unknown if the presence of anti-thyroglobulin (TgAb) and/or anti-thyroperoxidase antibodies (TPOAb) in AIT patients without other signs of an underlying thyroid disease may impair the response to glucocorticoid therapy.

METHODS

We performed a pilot retrospective cohort study with matched-subject design and an equivalence hypothesis, comparing the response to glucocorticoid therapy between 20 AIT patients with a normal thyroid gland, low radioiodine uptake, undetectable TSH receptor antibodies and positive TgAb and/or TPOAb (Ab+ group), and 40 patients with the same features and absent thyroid antibodies (Ab- group).

RESULTS

The mean cure time was 54 ± 68 days in the Ab+ group and 55 ± 49 days in the Ab- group (p = 0.63). The equivalence test revealed an equivalent cure rate after 60, 90 and 180 days (p = 0.67, 0.88 and 0.278, respectively). The occurrence of permanent hypothyroidism was higher in the Ab+ group than in the Ab- group (26.3 vs 5.13 %, p = 0.032).

CONCLUSIONS

The presence of TgAb and/or TPOAb does not affect the response to glucocorticoid therapy, suggesting that the patients with features of destructive form of AIT should be considered as having a type 2 AIT irrespective of the presence of TGAb or TPOAb. These patients have a higher risk of developing hypothyroidism after the resolution of thyrotoxicosis and should be monitored accordingly.

Dysfunction of the thyroid gland during amiodarone therapy: a study of 297 cases

AIM

This study aims to explore and compare the efficacy of radioiodine treatment (RIT) in hyperthyroid and euthyroid patients who have been treated with amiodarone (AM) in the past or are currently undergoing AM treatment. Clinical observation of a group of patients with amiodarone-induced hypothyroidism during a 12-month follow-up period was used for comparison.

DESIGN

This was a observational, two-centered study. Patients were assessed at baseline and at 2 months, 6 months, 8 months, and 12 months after RIT.

PATIENTS

Group A: At baseline (61 males [M] and 17 females [F], mean age 50±19 years), there were 78 euthyroid patients with cardiac arrhythmias, who were treated with AM and developed amiodarone-induced thyrotoxicosis, and currently require retreatment with AM. Group B: Hyperthyroid patients (92 M and 26 F, mean age 72±11.8 years) after AM therapy in the past. Group C: Hyperthyroid patients (66 M and 13 F, mean age 63.9±13.2 years) currently treated by AM. Group D: Hypothyroid patients (6 M and 16 F, mean age 61.4±10.4 years) after AM therapy. The patients from Groups A, B, and C were retreated with AM after ~3-6 weeks of RIT.

RESULTS

In Group A, after 12 months of RIT therapy, recurrent thyrotoxicosis was observed in six (7.7%) cases, and persistent hypothyroidism was diagnosed in 42 (53.8%) cases. In Group B, hyperthyroidism occurring during treatment with AM was found in 40 (33.9%) patients, and permanent hypothyroidism was observed in eleven (12.5%) cases. After annual follow-up in Group C, nine (11.4%) patients were diagnosed with hypothyroidism, while 27 (34.1%) patients were diagnosed with hyperthyroidism. In Group D, all patients had permanent hypothyroidism and when the concentration of serum thyroid-stimulating hormone was >10 µIU/mL, l-thyroxine was applied.

CONCLUSION

Our study showed that radioiodine administration is advisable in certain circumstances, even in euthyroid patients. It allows for continuation of further long-term AM treatment. Additionally, RIT allows for the reintroduction of AM therapy that was previously terminated. Hence, it can help control life-threatening tachyarrhythmias and decrease episodes of thyrotoxicosis.

Amiodarone-Induced Thyrotoxicosis Recurrence After Amiodarone Reintroduction

Reintroduction of amiodarone in patients with a history of amiodarone-induced thyrotoxicosis (AIT) is rarely used. To date, the risk of AIT recurrence after amiodarone reintroduction is unpredicted. The aim of the study was to evaluate the risk of AIT recurrence. Retrospectively, from 2000 to 2011, all euthyroid patients with a history of AIT with amiodarone reintroduction were included. Type and severity of the first AIT, amiodarone chronology, and thyroid function evolution after reintroduction of amiodarone were investigated: 46 of 172 patients with AIT history needed amiodarone reintroduction. At first AIT episode, the mean age was 62.2 ± 16 years with male gender predominance; 65% of patients were classified as type 1 AIT. AIT recurred in 14 patients (30%), 12 patients developed hypothyroidism (26%), and 20 patients remained euthyroid (44%). Characteristics of type 1 AIT during the first episode, namely briefer exposure period to amiodarone and longer duration of treatment to normalize thyroid hormones, were predictive of AIT recurrence; 73% of patients (8 of 11) with previous episode of type 1 AIT, who did not receive a preventive thioamide treatment, developed a second episode of AIT. Thioamide preventive treatment could be useful to prevent type 1 AIT recurrence. In conclusion, AIT recurrence after amiodarone reintroduction is 4 times more frequent in patients with type 1 AIT history. Thyroid ablation before amiodarone reintroduction in patients with a history of type 1 AIT is preferred. Preventive thioamide treatment could be suggested in patients with type 1 AIT history pending for surgery.

Thyrotoxicosis associated with the use of amiodarone: the utility of ultrasound in patient management

Amiodarone is an anti-arrhythmic drug that commonly affects the thyroid, causing hypothyroidism or thyrotoxicosis. Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive thyroid hormone biosynthesis in response to iodine load in autonomously functioning thyroid glands with pre-existing nodular goitre or underlying Graves' disease (type 1 or AIT 1), or by a destructive thyroiditis typically occurring in normal glands (type 2 or AIT 2). Indeterminate or mixed forms are also recognized. The distinction is clinically useful as AIT 1 is treated predominantly with thionamides, whereas AIT 2 is managed with glucocorticoids. We review the tools used to differentiate type 1 from type 2 thyrotoxicosis, with specific reference to the imaging modalities used.

Quantitative assessment of thyroid-to-background ratio improves the interobserver reliability of technetium-99m sestamibi thyroid scintigraphy for investigation of amiodarone-induced thyrotoxicosis

BACKGROUND

Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive hormone synthesis and release (AIT I), a destructive thyroiditis (AIT II), or a combination of both (AIT Ind). Although no gold-standard diagnostic test is available, technetium-99m sestamibi thyroid scintigraphy (99mTc-STS) has been previously reported to be an accurate tool for differentiating subtypes with important therapeutic implications. However, the information to guide reporting of 99mTc-STS is qualitative and highly subjective. This study aims to compare the interobserver reliability of 99mTc-STS before and after the use of quantitative thyroid-to-background ratios (TBRs) displayed on a time-activity curve for differentiation of AIT subtypes.

METHODS

A retrospective audit of Nuclear Medicine Departments at Royal Melbourne Hospital (Parkville, Victoria, Australia) and Cabrini Hospital (Malvern, Victoria, Australia) identified 15 consecutive 99mTc-STS studies performed for AIT. Four nuclear medicine physicians reported the studies according to previously established criteria (series 1). Quantitative TBR and estimated 'normal' range TBR were subsequently provided before the studies were reordered and reported again (series 2). Interobserver reliability was calculated using Fleiss' κ statistic for each assessment.

RESULTS

The overall percentage of agreement (PoA) and κ statistics for use of conventional 99mTc-STS for diagnosis of AIT improved from 47 to 80% and from 0.30 to 0.67 following the use of quantitative TBR displayed on a time-activity curve with reference to a normal population. Interobserver reliability improved substantially under all diagnostic comparisons, particularly for differentiation of either AIT I (PoA 80% to 94%, κ: 0.48 to 0.84) or AIT Ind (PoA 47% to 82%, κ: -0.05 to 0.51) from other types of AIT.

CONCLUSION

Use of quantitative TBR improves the interobserver reliability of reporting 99mTc-STS for investigation of different types of AIT. There is 'almost perfect' agreement upon differentiation of AIT I from AIT II and AIT Ind, with important implications for rationalizing the use of corticosteroid therapy. Prospective identification of AIT Ind is improved from 'poor' to a 'moderate' level of agreement to facilitate rational use of combination therapy at diagnosis.

Amiodarone-related thyroid dysfunction

Nowadays, amiodarone is the most commonly used antidysrhythmic drug in clinical practice. It is highly effective in the management of recurrent ventricular dysrhythmias, paroxysmal supraventricular dysrhythmias, including atrial fibrillation and flutter, and in the maintenance of sinus rhythm after electrical cardioversion of atrial fibrillation. Moreover, it has the added benefit of being well tolerated in patients with both normal and impaired left ventricular systolic function. Despite amiodarone's potent antidysrhythmic actions, its use is hampered by numerous adverse effects on various organs, including the thyroid. Adverse effects are becoming more prevalent given the increasing incidence of dysrhythmias and wider amiodarone use. Thus, physicians and patients should both be aware of the potential thyroid-specific sequelae. However, amiodarone is likely to remain a significant problem for endocrinologists as concerns exist over the use of the new alternative antiarrhythmic agent, dronedarone, especially in patients with heart failure and left ventricular dysfunction because of the risk of hepatic injury and increased mortality. The final diagnostic and therapeutic approaches must be discussed among the patient, the general practitioner, the cardiologist, and the endocrinologist.

Amiodarone-induced thyrotoxic thyroiditis: a diagnostic and therapeutic challenge

Amiodarone is an iodine-based, potent antiarrhythmic drug bearing a structural resemblance to thyroxine (T4). It is known to produce thyroid abnormalities ranging from abnormal thyroid function testing to overt hypothyroidism or hyperthyroidism. These adverse effects may occur in patients with or without preexisting thyroid disease. Amiodarone-induced thyrotoxicosis (AIT) is a clinically recognized condition commonly due to iodine-induced excessive synthesis of thyroid, also known as type 1 AIT. In rare instances, AIT is caused by amiodarone-induced inflammation of thyroid tissue, resulting in release of preformed thyroid hormones and a hyperthyroid state, known as type 2 AIT. Distinguishing between the two states is important, as both conditions have different treatment implications; however, a mixed presentation is not uncommon, posing diagnostic and treatment challenges. We describe a case of a patient with amiodarone-induced type 2 hyperthyroidism and review the current literature on the best practices for diagnostic and treatment approaches.

Cost effectiveness of a pharmacist-led information technology intervention for reducing rates of clinically important errors in medicines management in general practices (PINCER)

BACKGROUND AND OBJECTIVE

We recently showed that a pharmacist-led information technology-based intervention (PINCER) was significantly more effective in reducing medication errors in general practices than providing simple feedback on errors, with cost per error avoided at £79 (US$131). We aimed to estimate cost effectiveness of the PINCER intervention by combining effectiveness in error reduction and intervention costs with the effect of the individual errors on patient outcomes and healthcare costs, to estimate the effect on costs and QALYs.

METHODS

We developed Markov models for each of six medication errors targeted by PINCER. Clinical event probability, treatment pathway, resource use and costs were extracted from literature and costing tariffs. A composite probabilistic model combined patient-level error models with practice-level error rates and intervention costs from the trial. Cost per extra QALY and cost-effectiveness acceptability curves were generated from the perspective of NHS England, with a 5-year time horizon.

RESULTS

The PINCER intervention generated £2,679 less cost and 0.81 more QALYs per practice [incremental cost-effectiveness ratio (ICER): -£3,037 per QALY] in the deterministic analysis. In the probabilistic analysis, PINCER generated 0.001 extra QALYs per practice compared with simple feedback, at £4.20 less per practice. Despite this extremely small set of differences in costs and outcomes, PINCER dominated simple feedback with a mean ICER of -£3,936 (standard error £2,970). At a ceiling 'willingness-to-pay' of £20,000/QALY, PINCER reaches 59 % probability of being cost effective.

CONCLUSIONS

PINCER produced marginal health gain at slightly reduced overall cost. Results are uncertain due to the poor quality of data to inform the effect of avoiding errors.

Amiodarone-induced thyroid dysfunction in Taiwan: a retrospective cohort study

BACKGROUND

The incidence and risk factors of amiodarone-induced thyroid dysfunction are variable in the literature.

OBJECTIVE

The aim of this study was to investigate the clinical and biochemical features and risk factors of amiodarone-induced thyroid dysfunction in Taiwan.

SETTING

This study was conducted at a tertiary referral center for arrhythmia.

METHOD

Retrospective analysis of patients treated with amiodarone during the years 2008-2009 was performed.

MAIN OUTCOME MEASURE

Incidence and risk factors of amiodarone-induced thyrotoxicosis (AIT) and amiodarone-induced hypothyroidism (AIH) were assessed.

RESULTS

Of the 527 patients, 437 (82.9 %) remained euthyroid, 21 (4.0 %) developed AIT, and 69 (13.1 %) were affected with AIH. In univariate analysis, AIT was associated with younger age, and the risk factors for AIH included older age, higher baseline thyroid stimulating hormone (TSH) titer, lower baseline free T4 level, lower cumulative amiodarone dosage, and shorter amiodarone treatment duration. Cox regression analysis was performed to determine the different risk categories in the elderly population of age 65-74 (young-old), 75-84 (old-old), and ≥85 years old (oldest-old). Additionally increased risk of AIH was found in the groups of old-old (HR 2.09, 95 % CI 1.11-3.96) and oldest-old (HR 2.57, 95 % CI 1.21-4.75). In the multivariate analysis of risk factors for AIH, baseline TSH level (HR 1.38, 95 % CI 1.12-1.70) and cumulative amiodarone dosage (HR 0.95, 95 % CI 0.93-0.97) remained statistically significant.

CONCLUSION

AIH was much more common than AIT in Taiwan, an area with sufficient iodine intake. Higher baseline TSH level was the predominant independent risk factor for the development of AIH.

An audit of amiodarone-induced thyrotoxicosis--do anti-thyroid drugs alone provide adequate treatment?

INTRODUCTION

Amiodarone is a widely used anti-arrhythmic drug. A common long-term complication is amiodarone-induced thyrotoxicosis (AIT). We examined retrospectively the efficacy of anti-thyroid drugs with or without prednisolone and the role of surgical thyroidectomy in the treatment of AIT in a single centre, in an iodine-replete region of Australia.

METHODS

A retrospective audit of patients with AIT was performed between 2002-2012 at this centre. Twenty-seven patients, mean age 60.9 ± 2.3 years were identified. Medical therapy (anti-thyroid drugs, prednisolone) was commenced according to the treating endocrinologist. The main outcomes were time to euthyroidism and number proceeding to thyroidectomy.

RESULTS

Of 11 patients commenced on anti-thyroid drugs alone, seven (64%) required the addition of prednisolone. Baseline free T4 was significantly higher in those ultimately treated with prednisolone (58.4 ± 6.3pmol/L) versus those not (31.7 ± 3.4pmol/L, P<0.05). Although similar results were seen with free T3, the difference was not significant (P=0.06). In patients with baseline free T4 <30pmol/L, 75% (3/4) achieved euthyroidism without prednisolone. Neither the use of prednisolone nor continuation of amiodarone significantly influenced time to euthyroidism. Eleven patients (41%) proceeded to surgical thyroidectomy, which was undertaken by an experienced surgical team without significant complications and no mortality.

CONCLUSION

Patients with AIT generally required glucocorticoids. Mild disease (free T4 <30pmol/L) may be successfully treated with anti-thyroid drugs alone. Surgical thyroidectomy is a safe and effective treatment for those refractive to medical therapy.

[Hyperthyroidism]

Thyrotoxicosis is mainly caused by autonomous adenomas of the thyroid gland and by Graves' disease. A less frequent cause for thyrotoxicosis is Hashimoto's thyroiditis. Thyrotoxicosis in autonomous adenomas and Graves' disease is caused by an increased thyroid hormone production whereas hyperthyroidism in Hashimoto's thyroiditis results from destruction of the thyroid gland. Drug therapy depends on the cause of the disease. Autonomous adenomas and Graves' disease are treated with methimazole and potentially with β-blockers. Regarding thyroid ablative therapy, radioiodine is mostly preferred compared to thyroidectomy. Drug therapy of Hashimoto's thyroiditis is purely symptomatic using β-blockers and rarely corticosteroids. Hyperthyroidism in pregnancy is a major issue and pregnant women in the first trimester are treated with propylthiouracil (PTU) whereas women in the second and third trimesters are treated with methimazole. The aim is to maintain the serum fT4 levels within the upper normal range.

Iodine-induced thyroid dysfunction

PURPOSE OF REVIEW

To summarize the mechanisms of iodine-induced hypothyroidism and hyperthyroidism, identify the risk factors for thyroid dysfunction following an iodine load, and summarize the major sources of excess iodine exposure.

RECENT FINDINGS

Excess iodine is generally well tolerated, but individuals with underlying thyroid disease or other risk factors may be susceptible to iodine-induced thyroid dysfunction following acute or chronic exposure. Sources of increased iodine exposure include the global public health efforts of iodine supplementation, the escalating use of iodinated contrast radiologic studies, amiodarone administration in vulnerable patients, excess seaweed consumption, and various miscellaneous sources.

SUMMARY

Iodine-induced thyroid dysfunction may be subclinical or overt. Recognition of the association between iodine excess and iodine-induced hypothyroidism or hyperthyroidism is important in the differential diagnosis of patients who present without a known cause of thyroid dysfunction.

Body mass index and the development of amiodarone-induced thyrotoxicosis in adults with congenital heart disease--a cohort study

INTRODUCTION

Amiodarone-induced thyrotoxicosis (AIT) is a recognized complication of amiodarone treatment with limited management options. Its predisposing factors are incompletely defined yet a higher prevalence was reported in adults with congenital heart disease (CHD). Therefore we sought to determine the incidence and risk factors for AIT in adults with CHD.

METHODS

At a tertiary care center we followed a historical cohort of amiodarone-treated CHD patients for the period 1987-2009. Follow-up concluded at AIT diagnosis or with last thyroid assessment on amiodarone. Cumulative incidence of AIT was calculated. AIT association with nutritional status was hypothesized a priori.

RESULTS

AIT developed in 23/169 patients or 13.6%. The AIT incidence peaked in the 3rd year at 7.7%. AIT patients had a lower body mass index (BMI) at AMIO initiation compared with the rest of the cohort (mean ± standard deviation: 21.9 ± 2.9 vs. 25.1 ± 5.0; p<0.001). Patients with BMI<21 were more likely to develop thyrotoxicosis (RR=6.1) compared to those with BMI>25 (p<0.001). Presence of goiter was strongly associated with AIT (RR 3.6, p=0.002). Affected patients had a trend for higher cyanotic heart disease prevalence (34.8% vs. 17.8%, p=0.059). On multivariate analysis body mass index and goiter remained independent predictors of outcome.

CONCLUSIONS

BMI<21 at initiation of amiodarone therapy and presence of goiter are strong predictors of AIT in this population. Its incidence is time dependent. These predictors can be used clinically in assessing overall impact of amiodarone therapy in congenital heart disease patients.

Amiodarone and the thyroid: a 2012 update

Amiodarone-induced thyroid dysfunction occurs in 15-20% of amiodarone-treated patients. Amiodarone-induced hypothyroidism (AIH) does not pose relevant problems, is easily controlled by L-thyroxine replacement, and does not require amiodarone withdrawal. Most frequently AIH develops in patients with chronic autoimmune thyroiditis. Amiodarone- induced thyrotoxicosis (AIT) is most frequently due to destructive thyroiditis (type 2 AIT) causing discharge of thyroid hormones from the damaged, but otherwise substantially normal gland. Less frequently AIT is a form of hyperthyroidism (type 1 AIT) caused by the iodine load in a diseased gland (nodular goiter, Graves' disease). A clearcut differentiation between the two main forms is not always possible, despite recent diagnostic advances. As a matter of fact, mixed or indefinite forms do exist, contributed to by both thyroid damage and increased thyroid hormone synthesis. Treatment of type 1 (and mixed forms) AIT is based on the use of thionamides, a short course of potassium perchlorate and, if treatment is not rapidly effective, oral glucocorticoids. Glucocorticoids are the first-line treatment for type 2 AIT. Amiodarone should be discontinued, if feasible from a cardiac standpoint. Continuation of amiodarone has recently been associated with a delayed restoration of euthyroidism and a higher chance of recurrence after glucocorticoid withdrawal. Whether amiodarone treatment can be safely reinstituted after restoration of euthyroidism is still unknown. In rare cases of AIT resistance to standard treatments, or when a rapid restoration of euthyroidism is advisable, total thyroidectomy represents a valid alternative. Radioiodine treatment is usually not feasible due to the low thyroidal iodine uptake.

Determinants and outcome of amiodarone-associated thyroid dysfunction

OBJECTIVE

Amiodarone is frequently associated with thyroid dysfunction. Identifying predictors for amiodarone-associated thyroid dysfunction and assessing treatment outcome may aid clinicians in daily practice.

METHODS

We included 303 consecutive patients with amiodarone therapy for cardiac arrhythmias (260 with atrial fibrillation and 43 with ventricular arrhythmias). Thyroid function tests were performed every 6 months.

RESULTS

Mean age was 63 ± 12 years and 66% was male. After median follow-up of 3·3 (0·1-24) years, 23 (8%) patients developed amiodarone-associated thyrotoxicosis (incidence rate 1·9 per 100 person years) and 18 (6%) hypothyroidism (incidence rate 1·1 per 100 person years). The only predictor for amiodarone-associated thyrotoxicosis was age <62 years [HR = 2·4 (95% CI 1·0-5·7), P = 0·05]. Predictors for amiodarone-associated hypothyroidism were thyroid stimulating hormone >1·4 mU/l at baseline [HR = 5·1 (95% CI 1·1-22·4), P = 0·03], left ventricular ejection fraction <45% [HR = 3·8 (95% CI 1·1-13·3), P = 0·04] and diabetes mellitus at baseline [HR = 3·3 (95% CI 1·1-10·3), P = 0·04]. Gender was not a predictor for amiodarone-associated thyroid dysfunction. Five out of 12 (42%) patients with thyrotoxicosis exhibited spontaneous normalization of thyroid function on continuation of amiodarone therapy. Mean time to normalization in the total group was 6·2 ± 3·3 months, with no difference between continuing or discontinuing amiodarone (6·6 ± 3·8 vs 5·8 ± 2·8 months, P = 0·5).

CONCLUSIONS

During median follow-up of 3·3 years, the incidence of amiodarone-associated thyrotoxicosis was higher compared to hypothyroidism. Only general predictors for amiodarone-associated thyroid dysfunction were observed. Discontinuation of amiodarone did not influence treatment outcome.

Role of iodine in thyroid physiology

Adequate levels of iodine, a trace element variably distributed on the earth, are required for the synthesis of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). The iodide cycle consists of a series of transport, oxidation and coupling steps in thyroid follicular cells to produce thyroid hormone. The sodium/iodide symporter (NIS) transports iodide into the thyrocyte. Competitive inhibitors of NIS, such as perchlorate and thiocyanate, can decrease the entrance of iodide into the follicular cell. Pendrin is the primary protein that is responsible for iodide efflux out of the thyrocyte and into the follicular lumen. T₄ is deiodinated in target tissues to produce the active form of thyroid hormone, T₃, and other metabolites. Exposure to excessive iodine or chronic iodine deficiency may result in various clinical disorders. The Wolff-Chaikoff effect and Jöd-Basedow phenomenon describe mechanisms of thyroid autoregulation and dysregulation, respectively, during iodine excess. Population studies have determined that iodine deficiency exists in approximately 38% of the world's population, is the leading cause of preventable mental retardation, and is of particular concern to women and their infants. Finally, the unique role of iodine utilization in thyroid physiology has applications in many important clinical areas.

Approach to the patient with amiodarone-induced thyrotoxicosis

Amiodarone, a benzofuranic iodine-rich antiarrhythmic drug, causes thyroid dysfunction in 15-20% of cases. Although amiodarone-induced hypothyroidism poses no particular problem, amiodarone-induced thyrotoxicosis (AIT) is a diagnostic and therapeutic challenge. There are two main forms of AIT: type 1, a form of iodine-induced hyperthyroidism, and type 2, a drug-induced destructive thyroiditis. However, mixed/indefinite forms exist that may be caused by both pathogenic mechanisms. Type 1 AIT usually occurs in abnormal thyroid glands, whereas type 2 AIT develops in apparently normal thyroid glands (or small goiters). Diagnosis of thyrotoxicosis is easy, based on the finding of increased free thyroid hormone concentrations and suppressed TSH levels. Thyroid radioactive iodine (RAI) uptake values are usually very low/suppressed in type 2 AIT, most commonly low or low-normal, but sometimes normal or increased in type 1 AIT despite the iodine load. Color flow Doppler sonography shows absent hypervascularity in type 2 and increased vascularity in type 1 AIT. Mixed/indefinite forms may have features of both AIT types. Thionamides represent the first-line treatment for type 1 AIT, but the iodine-replete gland is not very responsive; potassium perchlorate, by inhibiting thyroid iodine uptake, may increase the response to thionamides. Type 2 AIT is best treated by oral glucocorticoids. The response very much depends on the thyroid volume and the severity of thyrotoxicosis. Mixed/indefinite forms may require a combination of thionamides, potassium perchlorate, and steroids. RAI is usually not feasible in AIT due to low RAI uptake values. Thyroidectomy represents a valid option in cases resistant to medical therapy.

Amiodarone and thyroid

Assessment of TSH and TPO-Ab before starting amiodarone (AM) treatment is recommended. The usefulness of periodic TSH measurement every 6 months during AM treatment is limited by the often sudden explosive onset of AIT, and the spontaneous return of a suppressed TSH to normal values in half of the cases. AM-induced hypothyroidism develops rather early after starting treatment, preferentially in iodine-sufficient areas and in females with TPO-Ab; it is due to failure to escape from the Wolff-Chaikoff effect, resulting in preserved radioiodine uptake. AM-induced thyrotoxicosis (AIT) occurs at any time during treatment, preferentially in iodine-deficient regions and in males. AIT can be classified in type 1 (iodide-induced thyrotoxicosis, best treated by potassium perchlorate in combination with thionamides and discontinuation of AM) and type 2 (destructive thyrotoxicosis, best treated by prednisone; discontinuation of AM may not be necessary). AIT is associated with a higher rate of major adverse cardiovascular events (especially of ventricular arrhythmias). Uncertainty continues to exist with respect to the feasibility of continuation of AM despite AIT, the appropriate methods to distinguish between AIT type 1 and 2 as well as the advantages of AIT classification into subtypes in view of possible mixed cases, and the best policy when AM needs to be restarted.

Glucocorticoids are preferable to thionamides as first-line treatment for amiodarone-induced thyrotoxicosis due to destructive thyroiditis: a matched retrospective cohort study

CONTEXT

Type 2 amiodarone-induced thyrotoxicosis (AIT) is a destructive thyroiditis usually responsive to glucocorticoids; however, recent surveys showed that many expert thyroidologists worldwide use thionamides for type 2 AIT patients.

OBJECTIVE

The objective of the study was to compare the effectiveness of methimazole (MMI) or prednisone (GLU) in type 2 AIT patients who had a short cure time according to a published predictive model.

DESIGN

This was a matched retrospective cohort study.

SETTING

The study was conducted at a university center.

PATIENTS

Forty-two untreated type 2 AIT patients with a predicted cure time < or = 40 d were divided into two groups (MMI and GLU groups). After matching for the predicted cure time, patients in the GLU group were selected in a 1:1 ratio to patients in the MMI group.

INTERVENTION

Patients were treated with GLU or MMI for 40 d. Patients still thyrotoxic after 40 d continued glucocorticoids if in the GLU group or were switched to prednisone (MMI-GLU group) if in the MMI group.

MAIN OUTCOME MEASURE

Time and rate of cure (healing) at 40 d were measured.

RESULTS

Patients still thyrotoxic after 40 d were 23.8 +/- 9.3% in the GLU group and 85.7 +/- 7.6% in the MMI group (P = 0.000). The GLU and MMI-GLU groups did not significantly differ in the nonhealing rate at 40 d (P = 0.730). When patients in the MMI group were treated with glucocorticoids, 94.1% patients achieved euthyroidism within 40 d. However, the global median cure time (MMI period + prednisone period) was longer (60 d, 95% confidence interval 53.5-66.5 d) in the MMI-GLU group than the GLU group (21 d, 95% confidence interval 15.1-26.9 d).

CONCLUSIONS

Glucocorticoids are the first-line treatment in type 2 AIT, whereas thionamides play no role in this destructive thyroiditis.

Amiodarone-induced thyrotoxicosis in a patient with autonomously functioning nodular goiter

OBJECTIVE

To report on adverse reactions associated with amiodarone and propylthiouracil.

CASE SUMMARY

A 64-year-old female with atrial fibrillation and nodular goiter progressed to overt thyrotoxicosis after receiving therapy with amiodarone 200 mg/day for less than 12 weeks. Thyroid scan revealed a hyperfunctioning nodule in the left lobe, while immunologic studies were negative for both thyroid peroxidase and thyroglobulin antibodies. The thyroid-stimulating hormone (TSH) receptor antibody level was transiently elevated. Propylthiouracil 100 mg 3 times/day was started after the withdrawal of amiodarone, but the patient developed severe generalized skin rash, fever, and leukocytosis after 4 weeks. Thyroidectomy was performed, and histopathology was compatible with type 1 amiodarone-induced thyrotoxicosis (AIT) associated with toxic nodular goiter. An objective causality assessment revealed that thyrotoxicosis was probably related to use of amiodarone.

DISCUSSION

Amiodarone is an antiarrhythmic agent that may cause thyroid dysfunction. Differentiating between the 2 types of AIT is important for implementation of the correct therapeutic strategy. The transient elevation of TSH receptor antibodies in AIT complicated the diagnosis. As a rare subtype, type 1 AIT by nodular goiter may be associated with early AIT. Initiating thyroid function monitoring within 3 months of amiodarone therapy should be considered.

CONCLUSIONS

Type 1 AIT caused by nodular goiter is rarely reported. Amiodarone should be avoided in such patients and subtotal thyroidectomy to remove the toxic nodule may be the treatment of choice.