Management of amiodarone-induced thyrotoxicosis in Latin America: an electronic survey

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.

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.

The Role of Thyroid Diseases and their Medications in Cardiovascular Disorders: A Review of the Literature

The association between thyroid disease and cardiovascular manifestations is significant and undeniable. Previous studies have explained several aspects of the effects of thyroid hormone on the heart and cardiovascular system. Accordingly, both hyper and hypothyroidism can cause important alterations in cardiac rhythm, output and contractility as well as vascular resistance and blood pressure. Since treating the thyroid abnormality, especially in its initial stages, could lead to a significant improvement in most of its resultant cardiovascular disturbances, early suspicion and recognition of thyroid dysfunction, is necessary in patients with cardiovascular manifestations. In this in-depth review, we discuss the physiological roles as well as the effects of abnormal levels of thyroid hormones on the cardiovascular system. We also review the effects of the medications used for the treatment of hyper and hypothyroidism on cardiac function. In the end, we discuss the association between thyroid function and amiodarone, an effective and frequently-used antiarrhythmic drug, because of its well-known effects on the thyroid.

[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.

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.

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.

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.

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.

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.

Benzofuran derivatives and the thyroid

Amiodarone and dronedarone are two clinically important benzofuran derivatives. Amiodarone has been used widely for treating resistant tachyarrhythmias in the past three decades. However amiodarone and its main metabolically active metabolite desethylamiodarone can adversely affect many organs, including the thyroid gland. Amiodarone-induced thyroid disorders are common and often present as a management challenge for endocrinologists. The pathogenesis of amiodarone-induced thyroid dysfunction is complex but the inherent effects of the drug itself as well as its high iodine content appear to play a central role. The non-iodinated dronedarone also exhibits anti-arrhythmic properties but appears to be less toxic to the thyroid. This review describes the biochemistry of benzofuran derivatives, including their pharmacology and the physiology necessary for understanding the cellular mechanisms involved in their actions. The known effects of these compounds on thyroid action are described. Recommendations for management of amiodarone-induced hypothyroidism and thyrotoxicosis are suggested. Dronedarone appears to be an alternative but less-effective anti-arrhythmic agent and it does not have adverse effects on thyroid function. It may have a future role as an alternative agent in patients being considered for amiodarone therapy especially those at high risk of developing thyroid dysfunction but not in severe heart failure.

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

OBJECTIVE

To investigate how North American thyroidologists assess and treat amiodarone-induced thyrotoxicosis (AIT) and to compare the results with those of the same questionnaire-based survey previously carried out among European thyroidologists.

DESIGN

Members of the American Thyroid Association (ATA) with clinical interests were sent by e-mail a questionnaire on the diagnosis and management of AIT, 115 responses were received from the United States and Canada, representing about one-third of ATA members with clinical interests.

RESULTS

The majority of respondents (91%vs. 68% in Europe, P < 0.05) see < 10 new cases of AIT per year, and AIT seems less frequent than amiodarone-induced hypothyroidism (AIH) in North America (34% and 66% of amiodarone-induced thyroid dysfunction, respectively, vs. 75% and 25%, respectively, in Europe, P < 0.001). When AIT is suspected, in North America hormonal assessment is mostly based on serum free T4 (FT4) and TSH measurements, while serum free T3 (FT3) determination is requested less frequently than in Europe; thyroid autoimmunity is included in the initial assessment less than in Europe. Most commonly used additional diagnostic procedures include, as in Europe, thyroid colour-flow Doppler sonography, and to a lesser extent, thyroid radioactive iodine uptake and scan, but Europeans tend to request multiple tests more than North Americans. Withdrawal of amiodarone is more often considered unnecessary by North American thyroidologists (21%vs. 10% in Europe in type 1 AIT, P < 0.05, 34%vs. 20% in type 2 AIT, P < 0.05). In type 1 AIT thionamides represent the treatment of choice for North Americans as well as for Europeans, but the former use them as monotherapy in 65%vs. 51% of Europeans (P < 0.05) who more often consider potassium perchlorate as an useful addition (31%vs. 15% of North Americans, P < 0.01). Glucocorticoids are the selected treatment for type 2 AIT, alone (62%vs. 46% in Europe, P < 0.05) or in association with thionamides (16%vs. 25% in Europe, P = NS). After restoration of euthyroidism, thyroid ablation in the absence of recurrent thyrotoxicosis is recommended in type 1 AIT less frequently by North Americans. If amiodarone therapy needs to be reinstituted, prophylactic thyroid ablation is advised by 76% in type 1 AIT, while a 'wait-and-see' strategy is adopted by 61% in type 2 AIT, similar to behaviour of European thyroidologists.

CONCLUSION

Similarities and differences exist between expert North American and European thyroidologists concerning the diagnosis and management of AIT. While differences reflect the frequent uncertainty of the underlying mechanism leading to AIT, similarities may represent the basis to refine the diagnostic criteria and to improve the therapeutic outcomes of this challenging clinical situation.

Differential diagnosis and appropriate treatment of four thyrotoxic patients with Graves' disease required to take amiodarone due to life-threatening arrhythmia

We report the treatment of four thyrotoxic patients. Two were cases of type I amiodarone-induced thyrotoxicosis (AIT) treated with methimazole. The third Graves' disease patient, who became hypothyroid 25 years after subtotal thyroidectomy, developed type II AIT. Furthermore, one case with heart failure and ventricular tachycardia, who developed an adverse reaction to antithyroid agents and was prescribed amiodarone, underwent total thyroidectomy. The clinical course was uneventful, and the patient is doing well. Since amiodarone contains a large amount of iodine, it is frequently difficult to make a differential diagnosis. Surgical treatment of Graves' disease patients is recommended when immediate control of hyperthyroidism and heart failure is required.

Thyroid disease and the heart

The cardiovascular signs and symptoms of thyroid disease are some of the most profound and clinically relevant findings that accompany both hyperthyroidism and hypothyroidism. On the basis of the understanding of the cellular mechanisms of thyroid hormone action on the heart and cardiovascular system, it is possible to explain the changes in cardiac output, cardiac contractility, blood pressure, vascular resistance, and rhythm disturbances that result from thyroid dysfunction. The importance of the recognition of the effects of thyroid disease on the heart also derives from the observation that restoration of normal thyroid function most often reverses the abnormal cardiovascular hemodynamics. In the present review, we discuss the appropriate thyroid function tests to establish a suspected diagnosis as well as the treatment modalities necessary to restore patients to a euthyroid state. We also review the alterations in thyroid hormone metabolism that accompany chronic congestive heart failure and the approach to the management of patients with amiodarone-induced alterations in thyroid function tests.

Glucocorticoid response in amiodarone-induced thyrotoxicosis resulting from destructive thyroiditis is predicted by thyroid volume and serum free thyroid hormone concentrations

CONTEXT

Amiodarone-induced thyrotoxicosis (AIT) resulting from destructive thyroiditis (type 2) is commonly treated with glucocorticoids, but time needed to restore euthyroidism may be unacceptable for patients with underlying cardiac disorders.

OBJECTIVE

The objective of this prospective study was to identify factors affecting the response to glucocorticoids in a large cohort of patients with type 2 AIT followed prospectively.

SETTING

This study was conducted at university centers.

PATIENTS

Sixty-six untreated patients with type 2 AIT were enrolled in the study.

INTERVENTION

All patients were treated with prednisone (initial dose, 0.5 mg/kg.d) as long as needed to restore euthyroidism, defined as cure of AIT.

MAIN OUTCOME MEASURE

The main outcome measure was cure time.

RESULTS

The median cure time was 30 d (95% confidence interval, 23-37 d). Serum free T4 concentration (picograms per milliliter) and thyroid volume (milliliters per square meter) (and, to a lesser extent, serum free T3 concentration) at diagnosis were the main determinants of response to glucocorticoids, with a cure hazard ratio of 0.97 (95% confidence interval, 0.95-0.99; P = 0.005) and 0.84 (95% confidence interval, 0.77-0.91; P = 0.000) for unit of increment, respectively. AIT was cured in all patients with a complete follow-up; euthyroidism was reached in 30 d or less in 60% of patients but in more than 90 d in 16%. A prompt control of thyrotoxicosis (<or=30 d of treatment) was more frequent (77%) in patients with serum basal free T4 concentration no greater than 50 pg/ml and thyroid volume (normalized for body surface area) no greater than 12 ml/m2. The cure probability and the mean cure time in an individual patient can be obtained using a formula generated by multiple regression models.

CONCLUSIONS

Baseline serum thyroid hormone concentrations and thyroid volume help identify patients with type 2 AIT at risk of a delayed response to glucocorticoids.