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

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.

Integrated Diagnostics of Thyroid Nodules

Thyroid nodules are common findings, particularly in iodine-deficient regions. Our paper aims to revise different diagnostic tools available in clinical thyroidology and propose their rational integration. We will elaborate on the pros and cons of thyroid ultrasound (US) and its scoring systems, thyroid scintigraphy, fine-needle aspiration cytology (FNAC), molecular imaging, and artificial intelligence (AI). Ultrasonographic scoring systems can help differentiate between benign and malignant nodules. Depending on the constellation or number of suspicious ultrasound features, a FNAC is recommended. However, hyperfunctioning thyroid nodules are presumed to exclude malignancy with a very high negative predictive value (NPV). Particularly in regions where iodine supply is low, most hyperfunctioning thyroid nodules are seen in patients with normal thyroid-stimulating hormone (TSH) levels. Thyroid scintigraphy is essential for the detection of these nodules. Among non-toxic thyroid nodules, a careful application of US risk stratification systems is pivotal to exclude inappropriate FNAC and guide the procedure on suspicious ones. However, almost one-third of cytology examinations are rendered as indeterminate, requiring "diagnostic surgery" to provide a definitive diagnosis. 99mTc-methoxy-isobutyl-isonitrile ([99mTc]Tc-MIBI) and [18F]fluoro-deoxy-glucose ([18F]FDG) molecular imaging can spare those patients from unnecessary surgeries. The clinical value of AI in the evaluation of thyroid nodules needs to be determined.

99m Tc-Sestamibi Thyroid Scintigraphy in Amiodarone-Induced Thyrotoxicosis : Functional Imaging-Histopathologic Correlation

ABSTRACT

99m Tc-sestamibi thyroid scintigraphy (STS) can aid in differentiating between types 1 and 2 amiodarone-induced thyrotoxicosis (AIT). We present a consecutive case series of 4 men (aged 56-75 years) in whom both 99m Tc-STS and thyroid histology were consistent with a diagnosis of type 2 AIT, representing the first reported histopathologic correlation for this diagnostic test. Median amiodarone treatment duration was 26 months (range, 10-39 months), and amiodarone was discontinued a median of 3 months preoperatively (range, 2-4 months) in all 4 cases. 99m Tc-STS is a promising functional imaging modality, which has the potential to aid clinicians in the diagnostic workup and treatment of AIT.

Functional and molecular thyroid imaging

Nuclear medicine methods were introduced in the 1940s for thyroid disease diagnosis and therapy. They is still a crucial part of thyroid nodules work-up. Thyroid imaging with iodine or iodine-analog isotopes is widely employed in patients with thyrotoxicosis and remains the only examination able to prove the presence of autonomously functioning thyroid tissue, which excludes malignancy with a high probability. In addition, technetium-99m-methoxyisobutylisonitrile ([^99mTc]Tc-MIBI) scintigraphy and positron emission tomography/computed tomography (PET/CT) with ¹⁸F-fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) are able to avoid unnecessary surgical procedures for cytologically inconclusive thyroid nodules, as confirmed by meta-analysis and cost-effectiveness studies. All considered thyroid molecular imaging allows functional characterization of different thyroid diseases, even before clinical symptoms become manifest, and remains integral to the management of such conditions. This paper summarizes main concepts of thyroid scintigraphy and its clinical use. In addition, it elaborates development of thyroid scintigraphy, as well as thyroid molecular imaging in patients with thyroid nodules and thyrotoxicosis.

Thyroid functional and molecular imaging

Radioiodine uptake (RAIU) test with iodine-123 (Na[¹²³I]I) or iodine-131 (Na[¹³¹I]I) enables accurate evaluation and quantification of iodine uptake and kinetics within thyroid cells. Thyroid Scintigraphy (TS) employing Na[¹²³I]I or ^99mTc-pertechnetate (Na[^99mTc]TcO₄) provides information regarding the function and topographical distribution of thyroid cells activity, including detection and localization of ectopic thyroid tissue. Destructive thyrotoxicosis is characterized by low RAIU with scintigraphically reduced radiotracer activity in the thyroid tissue, while productive thyrotoxicosis (i.e. hyperthyroidism "stricto sensu") is characterized by high RAIU with scintigraphically diffuse (i.e. Graves' Disease, GD and diffuse thyroid autonomy) or focal (i.e. autonomously functioning thyroid nodules, AFTN) overactivity. Accordingly, RAIU and/or TS are widely used to differentiate different causes of thyrotoxicosis. In addition, several radiopharmaceuticals are also available to help differentiate benign from malignant thyroid nodules and inform clinical decision-making: scintigraphic identification of AFTNs obviate fine-needle aspiration (FNA) biopsy, and [^99mTc]Tc-hexakis-(2‑methoxy-2-isobutyl isonitrile ([^99mTc]Tc-MIBI) and/or ¹⁸F-fluoro-d-glucose ([¹⁸F]FDG) may complement the work-up of cytologically indeterminate "cold" nodules for reducing the need for diagnostic lobectomies/thyroidectomies. Finally, RAIU studies are also useful for calculating the administered therapeutic activity of Na[¹³¹I]I to treat hyperthyroidism and euthyroid multinodular goiter. All considered, thyroid molecular imaging allows functional characterization of different thyroid diseases, even before clinical symptoms become manifest, and remains integral to the management of such conditions. Our present paper summarizes basic concepts, clinical applications, and potential developments of thyroid molecular imaging in patients affected by thyrotoxicosis and thyroid nodules.

Molecular Imaging for Thyrotoxicosis and Thyroid Nodules

After exclusion of exogenous iodine overload, radioiodine uptake (RAIU) testing with 123I or 131I enables the accurate evaluation and quantification of iodine uptake and kinetics within thyroid cells. In addition, scintigraphic evaluation with 123I or 99mTc-pertechnetate (99mTc04-) provides the topographic distribution of thyroid cell activity and allows the detection and localization of ectopic thyroid tissue. Destructive thyrotoxicosis is characterized by abolished or reduced uptake whereas productive thyrotoxicosis (i.e., hyperthyroidism "sensu strictu") is characterized by high RAIU with scintigraphically diffuse (i.e., Graves disease and diffuse thyroid autonomy) or focal (i.e., autonomously functioning thyroid nodules [AFTN]) overactivity. Accordingly, RAIU or thyroid scintigraphy are widely used to differentiate different causes of thyrotoxicosis. In addition, several radiopharmaceuticals are also available to help in differentiating benign from malignant thyroid nodules and inform clinical decision making. In fact, AFTNs can be safely excluded from fine-needle aspiration biopsy while either 99mTc-methoxyisobutylisonitrile (MIBI) and 18F-FDG may complement the work-up of cytologically indeterminate cold nodules and contribute to reducing the need for diagnostic lobectomies/thyroidectomies. Finally, RAIU studies are also useful for calculating the administered therapeutic activity of 131I to treat hyperthyroidism and euthyroid multinodular goiter. All considered, thyroid molecular imaging allows us to characterize molecular/functional aspects of different thyroid diseases, even before clinical symptoms become manifest and remains integral to properly managing such conditions. Our present paper summarizes basic concepts, clinical applications, and potential developments of thyroid molecular imaging in patients affected by thyrotoxicosis and thyroid nodules.

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.

[Clinical practice guidelines for acute and chronic thyroiditis (excluding autoimmune thyroiditis)]

Острые и хронические заболевания щитовидной железы занимают второе место по выявляемости после сахарного диабета. Всемирная организация здравоохранения отмечает ежегодную тенденцию к увеличению числа заболеваний щитовидной железы. В настоящих клинических рекомендациях будут рассмотрены вопросы этиологии, клинического течения, диагностики и лечения острых и хронических (за исключением аутоиммунного) воспалительных заболеваний щитовидной железы.Клинические рекомендации — это основной рабочий инструмент практикующего врача, как специалиста, так и врача узкой практики. Лаконичность, структурированность сведений об определенной нозологии, методов ее диагностики и лечения, базирующихся на принципах доказательной медицины, позволяют в короткий срок дать тот или иной ответ на интересующий вопрос специалисту, добиваться максимальной эффективности и персонализации лечения.Клинические рекомендации составлены профессиональным сообществом узких специалистов, одобрены экспертным советом Министерства здравоохранения РФ. Представленные рекомендации содержат максимально полную информацию, которая требуется на этапе диагностики острых и хронических тиреоидитов, этапе выбора тактики ведения пациентов с тиреоидитом, а также на этапе лечения пациента.Рабочая группа представляет этот проект в профессиональном журнале, посвященном актуальным проблемам эндокринологии, с целью повышения качества оказываемой медицинской помощи, повышения эффективности лечения острых и хронических тиреоидитов путем ознакомления с полным тестом клинических рекомендаций по острым и хроническим тиреоидитам (исключая аутоиммунный тиреоидит) максимально возможного количества специалистов в области не только эндокринологии, но и медицины общей (семейной) практики.

Thyroid effects of amiodarone: clinical update

PURPOSE OF REVIEW

Amiodarone-induced thyroid dysfunction is well established and commonly encountered but is associated with several diagnostic and management challenges. The present review discusses recent evidence published related to the effects of amiodarone on the thyroid gland and thyroid function.

RECENT FINDINGS

Retrospective studies to evaluate amiodarone-induced thyroid dysfunction in children show the occurrence of potential clinically significant changes within 2 weeks of amiodarone initiation that may not be detected if standard adult guidelines for thyroid hormone monitoring are followed. A small study evaluating beta-glucuronidase activity in amiodarone-induced thyrotoxicosis (AIT) demonstrated higher levels in patients with AIT type 2 compared to type 1. New data have suggested the incidence of agranulocytosis may be higher in patients on thionamides with AIT compared to hyperthyroidism because of other causes. In a small study, investigators demonstrated the use of a combination of intravenous and oral steroids to treat refractory AIT which needs to be evaluated in further controlled trials. Finally, recent data demonstrated a possible mortality benefit of surgery over medical therapy for AIT in patients with moderate to severe reduction in left ventricular ejection fraction.

SUMMARY

Recent research regarding the prevalence, diagnosis, and management of amiodarone-induced thyroid dysfunction were reviewed.

The Use of 99mTc-Methoxy-isobutyl-isonitrile (sestaMIBI) Uptake on Scintigraphy (99m-STS) in Amiodarone-Induced Thyrotoxicosis: Case Series and Review of the Literature

Amiodarone is a class III antiarrhythmic drug, used by cardiologists to treat arrhythmia including atrial fibrillation (A fib) and ventricular fibrillation. However, amiodarone is associated with endocrine dysfunction including both hypo- and hyperthyroidism. In the literature, two types of amiodarone-induced thyrotoxicosis (AIT) were described: AIT-1 and AIT-2. Mixed AIT also called AIT type 3 (AIT-3) has been described in the literature when the cases do not have a typical presentation. In order to differentiate different types of AIT, various clinical, biochemical, and radiological tools have been proposed. The use of ^99mTc-methoxy-isobutyl-isonitrile (sestaMIBI) uptake on scintigraphy (^99m-STS) has been suggested in the literature in only few studies (no large retrospective or prospective studies have been established in the United States). We present a case series describing 5 patients presenting to the University of Arizona with AIT where we used ^99m-STS to assess in diagnosis and treatment of different types of AIT followed by a review of the literature.

Amiodarone-Induced Thyrotoxicosis: Differential Diagnosis Using 99mTc-SestaMIBI and Target-to-Background Ratio (TBR)

PURPOSE OF THE REPORT

Distinguishing between amiodarone-induced thyrotoxicosis (AIT) caused by excessive hormone synthesis (AIT-1) or by a destructive process (AIT-2) has important therapeutic implications, but is still difficult and debated. Tc-sestaMIBI thyroid scintigraphy (99m-STS) has been proposed as a tool for classifying the two forms.

MATERIAL AND METHODS

30 AIT patients (11 females and 19 males) who underwent 99m-STS were retrospectively assessed for the present study. For each patient, a target-to-background ratio (TBR) was obtained on planar images. The TBR was then correlated with the qualitative assessment of the scans and the final clinical diagnosis.

RESULTS

Considering clinical response to treatment as the gold standard for differential diagnosis, 14 cases of AIT-1, 12 of AIT-2, and 4 mixed forms were identified. 99m-STS was able to qualitatively identify all the mixed forms, while 1/14 AIT-1 and 6/12 AIT-2 cases were misdiagnosed as mixed forms. When the quantitative index (the TBR) was compared with the final clinical diagnosis, ROC curve analysis enabled us to identify an IBR of 0.482 during 99m-STS as a cut-off capable of discriminating between AIT-1 and AIT-2, with 100% specificity and 91.7% sensitivity (P < 0.0001, area under the curve: 0.982).

CONCLUSIONS

Taking the TBR into consideration, 99m-STS proved a very useful tool for distinguishing AIT-1 from AIT-2, and thus offering patients appropriate treatment as of their diagnosis. This approach can avoid pointless and potentially dangerous combined overtreatments, and may speed up the return to normal thyroid function, which is crucial in AIT patients suffering from heart disease.

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.

Amiodarone-induced thyrotoxicosis: state of the art

В обзоре представлены данные литературы последних лет о патогенезе, диагностике, лечении амиодарон-индуцированного тиреотоксикоза (АИТ), который является частым осложнением терапии амиодароном (Ам). Описаны изменения секреции и метаболизма тиреоидныхгомонов под влиянием кратковременной и длительной терапии Ам. Развитие АИТ всегда приводит к ухудшению течения аритмии, усугублению недостаточности кровообращения, утяжелению состояния пациента. Выделяют АИТ 1 типа и АИТ 2 типа, а также смешанную форму. Описаны диагностические критерии АИТ 1 и 2 типа. Наиболее информативным тестом для дифференциальной диагностики АИТ 1, 2 типов и смешанных форм является сонография щитовидной железы с допплеровским исследованием кровотока и сканирование с 99mTc-sestaMIBI. Тактика лечения определяется типом АИТ, состоянием сердечно-сосудистой системы, риском повторных аритмий. Консервативное лечение зависит от типа АИТ и осуществляется тиреостатиками или глюкокортикоидами. Обсуждается возможность продолжения антиаритмической терапии Ам у пациентов, перенесших АИТ. При АИТ 1 типа и смешанной форме требуется отмена препарата, если это невозможно – радикальное лечение тиреотоксикоза (радиойодтерапия, тиреоидэктомия). АИТ 2 типа является самолимитирующимся процессом, при жизненно угрожающих аритмиях прием Ам может быть продолжен. Показана эффективность радиойодтерапии для радикального лечения тиреотоксикоза при АИТ 1 и 2 типа, несмотря на низкий захват радиойода. Однако этот вопрос требует дальнейшего изучения и обсуждения. Для быстрого восстановления эутиреоза у тяжелых больных применяют плазмаферез и тиреоидэктомию.

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.

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.