Desensitization to Methimazole

ObjectiveThionamides (methimazole and propylthiouracil) have been associated with common side effects, such as rash and pruritus, and rare but serious adverse effects, such as agranulocytosis and hepatotoxicity. Methimazole is usually the preferred thionamide for the treatment of hyperthyroidism if the patient is not planning to conceive or not in the first trimester of pregnancy, given the less frequent dosing and lower risk of hepatotoxicity. In patients who experience rash or itching when treated with methimazole, switching them to propylthiouracil is one treatment option. Here we report our experience regarding desensitization to methimazole to allow continued treatment with methimazole as an alternative management option.MethodsWe conducted a retrospective chart review of patients at a single institution who had side effects to methimazole and who were desensitized to methimazole under the supervision of an allergist. A total of 7 patients were included who experienced side effects to methimazole that did not include agranulocytosis or hepatotoxicity.ResultsAll 7 patients were able to take methimazole for treatment of their hyperthyroidism, either for continued medical therapy or as a bridge to definitive therapy, with either surgery or radioactive iodine treatment.ConclusionUnder the supervision of an allergist, desensitization to methimazole is an option for treating patients who experience side effects to methimazole (excluding agranulocytosis and hepatotoxicity).     

Delayed Antithyroid Drug-Induced Agranulocytosis

ObjectiveTo demonstrate that drug-induced agranulocytosis can occur after a very prolonged period of lowdose treatment with antithyroid medications.MethodsWe present the history and long-term follow-up of a patient with Graves disease, including clinical and laboratory findings, and provide a brief review of the related literature.ResultsA 53-year-old woman with a history of Graves disease presented with an absolute neutrophil count of zero, body temperature of 38.7°C, and symptoms of an upper respiratory tract infection. She had been treated continuously with low doses of antithyroid drugs for the preceding 11 years—propylthiouracil (100 to 150 mg daily) from February 1998 until July 2003 and methimazole (5 to 30 mg daily) from July 2003 until her presentation with severe neutropenia in March 2009. The daily dose of methimazole had been stable at 15 mg for 1 year before the current presentation. A thorough hematologic evaluation, including bone marrow biopsy, did not reveal an alternative cause for the agranulocytosis. After discontinuation of methimazole treatment and a short course of granulocyte colony-stimulating factor, she responded successfully with clinical improvement of her symptoms and resolved neutropenia.ConclusionAlthough this case is atypical, it reinforces the importance of remaining vigilant for signs of agranulocytosis throughout the course of treatment with antithyroid drugs, even at low doses and after years of continuous administration. (Endocr Pract. 2012;18:e69-e72)     

Thionamide-induced Agranulocytosis: A Retrospective Analysis of 36 Patients With Hyperthyroidism

ObjectiveAgranulocytosis is a rare but serious adverse drug reaction (ADR) of thionamide antithyroid drugs (ATDs). We explored the characteristics of ADRs in patients with hyperthyroidism.MethodsThis retrospective study included 3558 inpatients with Graves disease treated in a Class A Grade 3 hospital between 2015 and 2019. The clinical presentation and laboratory workup of patients with antithyroid drug (ATD)-induced agranulocytosis was analyzed.ResultsAgranulocytosis was thought to be caused by ATDs in 36 patients. The hospital length of stay was 12 (10-16) days, and hospitalization costs were approximately $2810.89 ($2156.50-$4164.67). The median duration of ATD therapy prior to agranulocytosis development was 30 (20-40) days. Fever (83.33%) and sore throat (75%) were the most common symptoms as early signs of agranulocytosis. The lowest neutrophil counts were 0.01 (0.00-0.03) × 10⁹/L and 0.14 (0.02-0.29) × 10⁹/L in the methimazole and propylthiouracil groups, respectively (P = .037). The recovery times of agranulocytosis were 9.32 ± 2.89 days and 5.60 ± 4.10 days in the methimazole and propylthiouracil groups, respectively (P = .016). Patients with severe agranulocytosis required a longer time to recover (P < .001) and had closer to normal serum thyroxine and triiodothyronine levels. The interval between the first symptom of agranulocytosis and ATD withdrawal was 1 (0-3) day.ConclusionsPatients with agranulocytosis needed a long hospital length of stay and incurred high costs. Methimazole was prone to causing a more serious agranulocytosis than propylthiouracil. High thyroid hormone was unlikely to play a role in adverse drug reactions. Patient education is important.     

Pharmacologic treatment of hyperthyroidism during pregnancy

Clinical hyperthyroidism has been associated with an increased risk of maternal, fetal, and neonatal complications. The available antithyroid drugs are methimazole/carbimazole and propylthiouracil. Several case reports and some epidemiologic studies suggest that methimazole/carbimazole exposure during the first trimester of pregnancy is associated with an increased risk of congenital malformations, including ectodermal anomalies, choanal atresia, esophageal atresia, and omphalocele. However, the absolute risk appears to be very small, and it remains unclear whether the association is driven by the maternal disease, the medication, or the combination of both factors. Propylthiouracil exposure has not been associated with an increased risk of congenital malformations and is the recommended drug during the first trimester of pregnancy. Since propylthiouracil-induced hepatotoxicity has been reported in approximately 0.1% of exposed adults and the number of case-reports of severe liver injury is increasing, treatment with low dose methimazole during the second and third trimesters should be considered. Until now, there has been no evidence that children prenatally exposed to methimazole/carbimazole or propylthiouracil have an increased risk of neurodevelopmental delay.     

Side Effects of PTU and MMI in the Treatment of Hyperthyroidism: A Systematic Review and Meta-Analysis

Objective: The present study aimed to investigate the adverse effects of the antithyroid drugs propylthiouracil (PTU) and methimazole (MMI)/carbimazole (CMZ) in treating hyperthyroidism.Methods: Qualitative analysis was performed for studies identified in a literature search up to April 20, 2019, and 30 studies were selected for meta-analysis. The study designs included case-control, randomized controlled, and retrospective cohort. Patients were in four age groups: childhood, gestating mothers, older adults, and other ages, and all were receiving PTU or MMI/CMZ. Adverse reactions to MMI/CMZ and PTU were evaluated and compared.Results: Odds of liver function injury were higher in the PTU group than in the MMI/CMZ group (odds ratio &lsqb;OR], 2.40; 95% confidence interval &lsqb;CI], 1.16 to 4.96; P = .02). Odds of elevated transaminase were much higher in the PTU group than in the MMI/CMZ group (OR, 3.96; 95% CI, 2.49 to 6.28; P<.00001). No significant between-group differences were found in odds of elevated bilirubin, agranulocytosis, rash, or urticaria; incidence of other adverse events; or in children. Odds of birth defects during the first trimester of pregnancy were higher in the MMI/CMZ group than in the PTU group (OR, 1.29; 95% CI, 1.09 to 1.53; P = .003).Conclusion: The impact of PTU on liver injury and transaminase levels is greater than that of MMI/CMZ, but no significant between-group differences are found in the drugs' effects on bilirubin, agranulocytosis and rash, urticaria, or in children. In treating pregnancy-related hyperthyroidism, PTU should be used in the first trimester and MMI reserved for use in late pregnancy.Abbreviations: ALT = alanine aminotransferase; ATD = antithyroid drug; CI = confidence interval; CMZ = carbimazole; GD = Graves disease; MMI = methimazole; MTU = methylthiouracil; NOS = Newcastle-Ottawa Scale; OR = odds ratio; PTU = propylthiouracil; RAI = radioactive iodine     

Successful Treatment of Thyroid Storm with Plasmapheresis in a Patient with Methimazole-Induced Agranulocytosis

ObjectiveTo report a case of a patient with Graves disease presenting with agranulocytosis induced by methimazole, with subsequent thyroid storm and successful therapeutic use of plasmapheresis.MethodsThe clinical features and laboratory findings in a patient with agranulocytosis and thyroid storm are presented, and the available literature on utilization of plasmapheresis in the setting of thyrotoxicosis is reviewed.ResultsA 40-year-old Vietnamese woman with Graves disease was admitted with methimazole-induced agranulocytosis. Treatment with methimazole was discontinued, and therapy with antibiotics, granulocyte colonystimulating factor, and ibuprofen was initiated. During hospitalization of the patient, her clinical status deteriorated, with development of pericarditis, thrombocytopenia, and thyroid storm. Treatment with plasmapheresis yielded near-euthyroidism in 3 days. Subsequently, she underwent successful total thyroidectomy.ConclusionOur case highlights the effectiveness of plasmapheresis when clinical situations prohibit the use of traditional treatment methods for thyrotoxicosis or thyroid storm (or both). (Endocr Pract. 2010;16:673-676)     

Hepatotoxicity from antithyroid drugs

We review the cases of hepatic injury from propylthiouracil, methimazole and carbimazole in the English language literature and compare them to cases of agranulocytosis in a recent review. The data on hepatotoxicity confirm the findings for agranulocytosis that low-dose methimazole is safer than propylthiouracil and that methimazole toxicity is more common over 40 years old. In contrast, propylthiouracil hepatotoxicity often occurs in younger patients. Most cases of hepatic injury occur in the first few months of drug therapy as with agranulocytosis. The reason that methimazole typically causes cholestatic hepatitis while propylthiouracil causes cytotoxic hepatitis remains unknown.     

Management of Thyrotoxicosis: Preconception,Pregnancy, and the Postpartum Period

Objective: To review the diagnosis and management of thyrotoxicosis in women who are preconception, pregnant, and in the postpartum period.Methods: Literature review of English-language papers published between 1980 and 2018.Results: Overt thyrotoxicosis occurs in 0.2% of pregnancies and subclinical thyrotoxicosis in 2.5%. Hyperthyroidism in women of childbearing age most frequently is caused by Graves disease (GD). Gestational thyrotoxicosis, transient human chorionic gonadotropin (hCG)-mediated hyperthyroidism, may develop in the first trimester. In the first year following delivery, postpartum thyroiditis, which frequently includes a thyrotoxic phase, occurs in 5% of women. Hyperthyroidism from nodular autonomy is uncommon in women of childbearing age. It is essential to understand the underlying etiology for thyrotoxicosis in order to recommend appropriate treatment. Gestational thyrotoxicosis requires supportive care, without antithyroid drug therapy. GD may be treated with antithyroid drugs, radioactive iodine, or thyroidectomy. Pregnancy, plans for pregnancy, and lactation have important implications for the choice of GD treatment. When thyrotoxicosis presents following delivery, postpartum thyroiditis must be differentiated from GD.Conclusion: The diagnosis and management of thyrotoxicosis in the peripregnancy period present specific challenges. In making management decisions, it is essential to weigh the risks and benefits of treatments not just for the mother but also for the fetus and for breastfed infants. A team approach to management is critical, with close collaboration among endocrinologists, maternal-fetal medicine specialists, and neonatologists.Abbreviations: GD = Graves disease; hCG = human chorionic gonadotropin; MMI = methimazole; PPT = postpartum thyroiditis; PTU = propylthiouracil; T3 = triiodothyronine; T4 = thyroxine; TBG = thyroxine-binding globulin; TRAb = TSH receptor antibody; TSH = thyroid-stimulating hormone     

A 2017 Survey of the Clinical Practice Patterns in the Management of Relapsing Graves Disease

Objective: Previous surveys from different world regions have demonstrated variations in the clinical management of Graves disease (GD). We aimed to investigate the clinical approach to GD relapse among endocrinologists.Methods: Electronic questionnaires were e-mailed to all members of the Israeli Endocrine Society. Questionnaires included demographic data and different scenarios regarding treatment and follow-up of patients with GD relapse.Results: The response rate was 49.4% (98/198). For a young male with GD relapse, 68% would restart antithyroid drug (ATD) (98% methimazole), while 32% would refer to radioactive iodine (RAI) treatment. Endocrinologists who treat >10 thyroid patients a week tended to choose ATDs over RAI (P = .04). In the case of GD relapse with ophthalmopathy, 50% would continue ATDs, whereas 22.4% would recommend RAI treatment and 27.6% surgery. Most endocrinologists (56%) would continue ATDs for 12 to 24 months. Seventy-five percent would monitor complete blood count and liver function (39% for the first month and 36% for 6 months), and 44% would recommend a routine neck ultrasound. In a case of thyrotoxicosis due to a 3-cm hot nodule, most endocrinologists (70%) would refer to RAI ablation, 46.4% without and 23.7% with a previous fine-needle aspiration. No significant differences were found regarding gender, year of board certification, or work environment.Conclusion: Our survey demonstrates diverging patterns in the diagnosis and management of GD relapse that correlate well with previous surveys from other countries on GD-naïve patients and a less than optimal adherence to recently published clinical guidelines.Abbreviations: ATA = American Thyroid Association; ATD = antithyroid drug; CBC = complete blood count; GD = Graves disease; GO = Graves ophthalmopathy; LFT = liver function test; MMI = methimazole; PTU = propylthiouracil; RAI = radioactive iodine; TSI = thyroid-stimulating immunoglobulin     

Unusual Clinical Course of Graves’ Thyrotoxicosis and Concomitant Sarcoidosis: Case Report and Review of Literature

ObjectiveTo report a case of Graves’ disease with concomitant sarcoidosis involving the thyroid gland.MethodsWe present the clinical, laboratory, imaging, and pathologic findings and describe the clinical course of a patient with Graves’ disease and sarcoidosis, who was unresponsive to propylthiouracil and radioiodine treatment.ResultsA 23-year-old woman presented with thyrotoxicosis and a large goiter. Laboratory studies and findings on thyroid uptake and scan were consistent with Graves’ disease. She was also found to have hilar lymph-adenopathy and hepatosplenomegaly. Despite treatment with antithyroid drugs and radioiodine therapy, her hyperthyroidism persisted. Surgical resection of the thyroid gland and 2 lymph nodes disclosed noncaseating granulomas, consistent with sarcoid.ConclusionAutoimmune endocrinopathies and, less commonly, thyroid autoimmune disease have been reported in patients with sarcoidosis. Similarities exist in the pathogenesis of these two conditions. Concomitant sarcoidosis in the thyroid gland in patients with Graves’ disease may contribute to the resistance to antithyroid drugs and radioiodine therapy. (Endocr Pract. 2007;13:159-163)     

A Case of Gestational Thyrotoxicosis Associated With Wernicke’s Encephalopathy

ObjectiveTo present a case of gestational thyrotoxicosis and hyperemesis gravidarum associated with Wernicke’s encephalopathy.MethodsWe present a detailed case report with the clinical, imaging, and laboratory findings of the patient and review the pertinent literature.ResultsA 36-year-old woman at 14 weeks of gestation was admitted to the hospital for management of severe hyperemesis gravidarum (HG). While hospitalized, she developed low-grade fever, tachycardia, hypotension, and altered mentation. Laboratory tests were diagnostic of hyperthyroidism. Physical examination revealed a confused, lethargic woman with a normal-size thyroid and pendular nystagmus in primary and lateral gaze. She was treated empirically for thyroid storm with methimazole and other measures. A brain magnetic resonance imaging (MRI) study done later showed hyperintense abnormal signals in bilateral thalamic regions, consistent with Wernicke’s encephalopathy (WE). She was immediately started on intravenous thiamine and her mental status improved considerably within 3 to 4 days. Within 2 weeks, the patient’s thyroid-function tests normalized and methimazole was discontinued. A repeat brain MRI 6 months later showed marked reduction of signal intensity in both thalamic regions.ConclusionThis case demonstrates that gestational thyrotoxicosis in a patient with HG can precipitate acute WE, which may mimic thyroid storm and thus delay appropriate management of this neurologic disorder. We conclude that prophylactic thiamine administration may be considered before caloric replacement in patients who present with HG and acute neurologic dysfunction. (Endocr Pract. 2014;20:e237-e240)     

Treatment of amiodarone induced hyperthyroidism with potassium perchlorate and methimazole during amiodarone treatment.

To exploit the antiarrhythmic effect of amiodarone when patients develop the side effect of thyrotoxicosis three patients with hyperthyroidism induced by amiodarone were given simultaneously 1 g potassium perchlorate a day for 40 days and a starting dose of 40 mg methimazole a day while they continued to take amiodarone. As hyperthyroidism might have recurred after potassium perchlorate treatment was stopped the dose of methimazole was not reduced until biochemical hypothyroidism (raised thyroid stimulating hormone concentrations) was achieved. The patients became euthyroid (free triiodothyronine concentration returned to normal values) in two to five weeks and hypothyroid in 10 to 14 weeks. One patient became euthyroid while taking 5 mg methimazole a day and 600 mg amiodarone weekly; the two others required substitution treatment with thyroxine sodium while taking 5 mg methimazole or 50 mg propylthiouracil (because of an allergic reaction to methimazole) and 2100 or 1400 mg amiodarone weekly. Hyperthyroidism induced by amiodarone may be treated with potassium perchlorate and methimazole given simultaneously while treatment with amiodarone is continued.     

Destructive Thyroiditis Followed by Hypothyroidism Associated with Infliximab Therapy

ObjectiveTo present the rare case of a patient who developed destructive thyroiditis accompanied by transient thyrotoxicosis resulting from infliximab therapy for the treatment of psoriasis.MethodsThe clinical presentation and management of a case with infliximab-associated thyroiditis is described with a brief review of the literature.ResultsA 57-year-old male who suffered from psoriasis was treated with infliximab therapy for 4 years. Thyroid function tests were normal before infliximab therapy. When the patient presented in our clinic, he had thyrotoxicosis and was using propylthiouracil. A 99m Technetiumpertechnetate thyroid scintigraphy scan showed no visualization of either thyroid lobe or decreased thyroid iodine uptake. Thyroid-stimulating hormone (TSH) receptor antibody, thyroid peroxidase antibody (anti-TPO Ab) and thyroglobulin antibody (anti-Tg Ab) were negative. Thyroid ultrasonography revealed a heterogeneous thyroid gland without nodules. After stopping propylthiouracil therapy, we advised monitoring of his thyroid function tests in the following weeks, and infliximab therapy for psoriasis was continued. Four weeks later, his thyroid function tests showed an elevated TSH level with normal levels of free triiodothyronine and thyroxine (FT3 and FT4, respectively), and levothyroxine treatment was administered to the patient. Thyroid function tests normalized after levothyroxine treatment. One year later, infliximab therapy was stopped because of clinical remission. Simultaneously, levothyroxine treatment was also stopped. His thyroid function tests were normal 6 weeks after the cessation of levothyroxine treatment.ConclusionTo our knowledge, the present report is the third infliximab-associated thyroid disorder case. Periodic follow-up of thyroid function tests is necessary during infliximab therapy. (Endocr Pract. 2014;20:e207-e210)     

Congenital Anomalies in Children Exposed to Antithyroid Drugs In-Utero: A Meta-Analysis of Cohort Studies

BackgroundHyperthyroidism affects about 0.2%-2.7% of all pregnancies, and is commonly managed with antithyroid drugs (ATDs). However, previous studies about the effects of ATDs on congenital anomalies are controversial. Therefore, the present meta-analysis was performed to explore the risk of congenital anomalies in children exposed to ATDs in-utero.MethodsEmbase, Pubmed, Web of Knowledge, and BIOSIS Citation Index were searched to find out studies about congenital anomalies in children exposed to ATDs in-utero reported up to May 2014. The references cited by the retrieved articles were also searched. The relative risks (RRs) and confidence intervals (CIs) for the individual studies were pooled by fixed effects models, and heterogeneity was analyzed by chi-square and I² tests.ResultsEight studies met the inclusion criteria. Exposure to propylthiouracil (PTU), methimazole/carbimazole (MMI/CMZ), and PTU & MMI/CMZ was investigated in 7, 7 and 2 studies, respectively. The pooled RR was 1.20 (95%CI: 1.02-1.42), 1.64 (95%CI: 1.39-1.92), and 1.83 (95%CI: 1.30-2.56) for congenital anomalies after exposure to PTU, MMI/CMZ, and PTU & MMI/CMZ, respectively.ConclusionsThe meta-analysis suggests that exposure to ATDs in-utero increases the risk of congenital anomalies. The use of ATDs in pregnancy should be limited when possible. Further research is needed to delineate the exact teratogenic risk for particular congenital anomaly.     

Long-Term Outcomes of Radioiodine Therapy for Juvenile Graves Disease with Emphasis on Subsequently Detected Thyroid Nodules: A Single Institution Experience from Japan

Objective: To investigate the long-term outcomes of radioiodine therapy (RIT) for juvenile Graves disease (GD) and the ultrasonographic changes of the thyroid gland.Methods: All of 117 juvenile patients (25 males and 92 females, aged 10 to 18 &lsqb;median 16] years) who had undergone RIT for GD at our clinic between 1999 and 2018 were retrospectively reviewed. Each RIT session was delivered on an outpatient basis. The maximum ¹³¹I dose per treatment was 13.0 mCi, and the total ¹³¹I dose per patient was 3.6 to 29.8 mCi (median, 13.0 mCi). ¹³¹I administration was performed once in 89 patients, twice in 26, and three times in 2 patients. Ultrasonography of the thyroid gland was regularly performed after RIT. The duration of follow-up after the initial RIT ranged from 4 to 226 (median 95) months.Results: At the latest follow-up more than 12 months after RIT (n = 111), the patients' thyroid functions were overt hypothyroidism (91%), subclinical hypothyroidism (2%), normal (5%), or subclinical hyperthyroidism (2%). New thyroid nodules were detected in 9 patients, 4 to 17 years after initial RIT. Patients with newly detected thyroid nodules underwent RIT with lower doses of ¹³¹I and had larger residual thyroid volumes than those without nodules. None of the patients were diagnosed with thyroid cancer or other malignancies during the follow-up period.Conclusion: Over a median follow-up period of 95 months (range, 4 to 226 months), RIT was found to be effective and safe in juvenile GD. However, cumulative evidence from further studies is required to confirm the long-term safety of RIT for juvenile GD.Abbreviations: ATD = antithyroid drug; GD = Graves disease; KI = potassium iodide; LT4 = levothyroxine; MMI = methimazole; PTU = propylthiouracil; RAIU = radio-active iodine uptake; RIT = radioiodine therapy; ^99mTc = technetium-99m; TSH = thyrotropin     

Thyroid hormone autoantibodies (THAA) in two cases of Graves' disease: effects of antithyroid drugs, prednisolone, and subtotal thyroidectomy

Changes in titers of serum thyroid hormone autoantibodies (THAA) and anti-thyroglobulin (Tg) antibodies during treatment with antithyroid drugs (methimazole and propylthiouracil) were examined in two cases of Graves' disease. Effects of prednisolone and subtotal thyroidectomy were also investigated in one case (case 1). Initially both cases had only anti-T4 autoantibodies in their serum. During methimazole therapy, the titer of anti-T4 autoantibodies increased in both cases, and anti-T3 autoantibodies became detectable and their titer increased in case 2. The influence of propylthiouracil on the titer of THAA was not clear. Both prednisolone plus methimazole therapy and subtotal thyroidectomy decreased the level of anti-T4 autoantibodies in case 1. There was a significant correlation between titers of THAA and anti-Tg antibodies in both cases, although titers of anti-Tg antibodies in case 1 stayed within the normal range throughout the investigation period. These results indicate that methimazole treatment could induce and/or enhance the production of THAA and THAA are antibodies against thyroid hormone-containing Tg molecule.     

Metabolism of 35S-labelled Antithyroid Drugs in Man

Differences in the metabolic fate of antithyroid drugs influence the optimal frequency of administration and their therapeutic efficacy. ³⁵S propylthiouracil differed from the ³⁵S imidazoles (carbimazole and methimazole) in the more rapid absorption and excretion and the shorter biological half-life in the plasma of the former. Renal function may have a more important influence on the biological half-life of the drugs than thyroid status. Further work is required to determine the optimal frequency of administration for each compound.     

MANAGEMENT OF DIABETES MELLITUS ON YOM KIPPUR AND OTHER JEWISH FAST DAYS

ObjectiveTo create guidelines for patients with diabetes to fast safely on Yom Kippur and other Jewish fast days, with the primary goal of avoiding hypoglycemia.MethodsAlmost 30 years of experience in endocrinology and the pharmacokinetics and pharmacodynamics of current drug therapy were applied to develop these guidelines and recommendations. A few illustrative cases are presented.ResultsPatients with either type 1 or type 2 diabetes were able to fast safely when a treatment plan was proactively formulated before the fast day. An understanding of which medications lower basal and which lower prandial blood glucose levels, as well as their duration of action, is critical.ConclusionThe overwhelming majority of patients with type 1 or type 2 diabetes can, from the perspective of blood glucose control, safely fast on Yom Kippur. Physician-patient discussion is important to prevent the patient from relying only on personal judgment and potentially taking too much medication, with the resultant development of hypoglycemia. (Endocr Pract. 2008;14: 305-311)     

Serial Changes of Liver Function Tests before and during Methimazole Treatment in Thyrotoxic Patients

Objective: Overt hyperthyroidism and methimazole (MMI) treatment are frequently associated with abnormal liver function tests (LFTs). We describe the serial changes of LFTs in MMI-treated hyperthyroid patients.Methods: We retrospectively analyzed all 77 patients presenting with newly diagnosed overt hyperthyroidism (59 Graves diseases, 11 toxic nodular goiters, 4 toxic adenomas, 3 amiodarone-induced thyrotoxicosis) between 2012 and 2014. All patients started MMI at 10 to 60 mg/day that was gradually tapered. We measured thyroid-stimulating hormone, free thyroxine, alanine aminotransferase (ALT) and aspartate aminotrasnferase (AST) at baseline and at 6 weeks, 4.5 months and 10 months after starting the MMI treatment. The concomitant medication was stable during MMI treatment.Results: At baseline, 25 patients (32.5%) had abnormal LFT, of which 5 had ALT or AST levels >2× the upper limit of normal (ULN). In most patients with baseline abnormal LFT, MMI treatment resulted in a normalization of serum ALT and AST. Thirteen patients with normal baseline LFT had <2× the ULN elevations of LFT sometime during treatment. There was a case of significant hepatotoxicity. During treatment, there were no significant differences in LFT levels between patients with initially normal or abnormal LFT. In a Cox proportional hazard regression model, abnormal LFT at baseline, abnormal thyroid function at the last evaluation, and MMI dose were not predictors of abnormal LFT at the final evaluation.Conclusion: MMI treatment can induce insignificant LFT elevation, <2× the ULN. MMI can be safely administered in hyperthyroid patients with abnormal LFT, and normalization of increased AST and ALT levels should be anticipated.Abbreviations:ALT = alanine aminotransferaseAST = aspartate aminotransferasefT4 = free thyroxineHCV = hepatitis C virusLFT = liver function testLOCF = last observation carried forwardMMI = methimazolePTU = propylthiouracilTSH = thyroid-stimulating hormoneULN = upper limit of normal