The Influence of Antithyroid Drug Discontinuation to the Therapeutic Efficacy of (131)I in Hyperthyroidism

Effect of previous administration of potassium iodine and different durations of low iodine diets for radioiodine therapy on the treatment of Graves' disease in iodine-rich areas

PURPOSE

To examine whether adherence to a low-iodine diet (LID) enhances the therapeutic efficacy of radioiodine therapy (RAI) in Graves' hyperthyroidism (GH) in iodine-rich areas.

METHODS

We retrospectively evaluated 185 patients with GH from Aichi (n = 114) and Hokkaido (n = 71) Prefectures. Patients aged ≥ 18 years with GH who underwent RAI between December 2012 and March 2022 were divided into subgroups based on pretreatment with anti-thyroid drug (ATD) or potassium iodide (KI). Patients were followed up with LID from 18 days (group A) or 7 days (group H) before RAI to 3 days after RAI. The dose of radioactive iodine 131 (131I) was adjusted to deliver > 100 Gy to the thyroid. The associations between urinary iodine concentration on UIC2 vs. 24hRU and UIC2 vs. the 1-year RAI success rate (SR) were investigated.

RESULTS

Compared with UIC1, UIC2 was significantly decreased in all subgroups (P < 0.01). An inverse correlation between UIC2 and 24hRU was observed in the four groups; however, the difference was insignificant. The SR in groups A and H was 85% and 89%, respectively. Univariate analysis revealed no association between UIC2 and SR in each group. Additionally, stratification of the 185 patients into quartiles using UIC2 yielded no significant differences in SR (p = 0.79).

CONCLUSIONS

LID sufficiently reduced UIC in patients undergoing RAI. Although a lower UIC2 may increase 24hRU, it did not increase the success of RAI. The benefit of LID in enhancing the efficacy of RAI in GH treatment remains uncertain.

The influence of thionamides on intra-thyroidal uptake of 131I during radioiodine-131 treatment of Graves' disease

Graves' disease is one of the most common causes of hyperthyroidism. Guideline recommendations advocate the intake of thionamides for at least 1 year. If hyperthyroidism persists, subsequent radioiodine-131 treatment (RIT) is a therapeutic option. Thionamides are known to influence intra-thyroidal bio-kinetics of iodine and should therefore be discontinued at least 3 days prior to RIT if possible. However, the required therapeutic activity has to be calculated individually by pre-therapeutic measurement of the uptake prior to RIT [radioiodine-131 uptake test (RIUT)] in Germany according to national guidelines. Therefore, the aim of this study was to quantify the influence of thionamides on intra-therapeutic uptake. A cohort of 829 patients with Graves' disease undergoing RIUT and RIT was analysed. Patients were subdivided into three groups. Group A: patients with carbimazole medication (n = 312), group B: patients with methimazole medication (n = 252) and group C: patients without thionamides (n = 265). Group A and B were further subdivided depending on the reduction of dosage of thionamides. In order to analyse the influence of thionamides, the variance of the determined individual extrapolated maximum intra-thyroidal uptake (EMU) between RIUT and RIT within the single groups and within the subgroups was statistically evaluated. When administering an equal dose of thionamides or no thionamides in RIUT and RIT (groups A1, B1 and C) no significant differences were detected when comparing EMU in RIT to EMU in RIUT (p > 0.05). In the subgroups A2-A4 (reduced dosage of carbimazole prior to RIT) EMU was significantly increased in RIT compared to RIUT [21% for a reduction of 0 to < 10 mg/d (A2), 39% for a reduction of 10-15 mg/d (A3) and 80% for a reduction of > 15 mg/d (A4)]. In the subgroups B2-B4 (reduced dosage of methimazole prior to RIT) EMU was as well significantly increased in RIT compared to RIUT [26% for a reduction of 0 to < 10 mg/d (B2), 36% for a reduction of 10-15 mg/d (B3) and 59% for a reduction of > 15 mg/d (B4)]. A significant dose-dependent increase of EMU in RIT compared to EMU in RIUT in patients discontinuing or reducing thionamides was detected. Therefore, thionamides should be discontinued at least 2 days prior to RIUT in order to achieve the designated target dose more precisely and to minimize radiation exposure of organs at risk.

Effect of iodine-therapy on hyperthyroidism patients without pre-administration of anti-thyroid therapeutic options

Anti-thyroid treatment and radioiodine are mainly used treatments for patients with thyrotoxicosis. The effect of anti-thyroid drugs (ATDs) on radioactive iodine's therapeutic effectiveness in hyperthyroidism remains controversial. This study aimed to determine the treatment effectiveness and complications in patients with thyrotoxicosis receiving radioiodine treatment with or without adjunctive anti-thyroid drugs in a tertiary endocrinology center in Ahvaz, Iran. A total of 165 patients with thyrotoxicosis (50 males and 115 females) were recruited in this retrospective clinical study. These patients were divided into two groups: one group underwent natural iodine therapy without being treated with anti-thyroid drugs (N= 86), and the other group was first treated with anti-thyroid drugs and then treated with iodine (N= 79). Then, the frequency of euthyroidism, thyroid storm, thyroiditis, hypothyroidism and the time to reach euthyroidism is evaluated. The results showed no difference between the two groups when reaching the euthyroid and the mean numerical mean TSH at the time of hypothyroidism. However, the average dose of iodine received in the concomitant drug group was lower. No thyroid storm was observed in the two groups regarding complications after treatment. Also, the prevalence of hypothyroidism and thyroiditis were not significantly different between the two groups. Iodine therapy with and without the use of anti-thyroid drugs (ATD) in low-risk patients with thyrotoxicosis has no difference in treatment outcomes, response to treatment, and subsequent complications.

Clinical efficacy of fixed-dose radioactive iodine for the treatment of hyperthyroidism at a single centre: our experience

BACKGROUND

Iodine-131 is an effective treatment for thyrotoxicosis. In 2019, National Institute for Clinical Excellence guidelines (UK) suggested offering radioactive iodine as first-line definitive treatment for adults with Graves' disease, toxic nodular and multinodular goitre unless it is unsuitable or anti-thyroid drugs are likely to achieve remission. The aim of this study was to evaluate the clinical outcome 1 year after using fixed-dose Iodine-131 for hyperthyroidism and time (months) to response.

METHODS

Electronic patient records were studied retrospectively for all patients who were treated with radioiodine therapy for hyperthyroidism between July 2017 and March 2020 at a district general hospital in the UK. Response to radioiodine therapy was initially assessed at 6 weeks and then at 3, 6, and 12 months by a dedicated thyroid nurse-led virtual follow-up.

RESULTS

We identified 67 patients with a mean age of 55.9 years (range 18-84); 48 (72%) females, 19 (28%) males. Of these, 57 (85%) patients were cured at 12 months (93.7% in non-Graves', 82.3% in Graves' group). Gender, diagnosis and pre-treatment disease interval were not significantly associated with treatment success. Non-Graves' patients had a significantly shorter time to discharge than Graves' patients receiving Iodine-131 (8 versus 10.3 months, p = 0.0174).

CONCLUSION

The results of the present study demonstrate that a single fixed dose of Iodine-131 therapy is highly effective and comparable to outcomes from calculated dose therapy in literature. We propose the routine use of scoring system to calculate risk of relapse for all newly diagnosed hyperthyroid patients to tailor treatment modality.

Ventricular Fibrillation: Potential Deadly Consequence of Discontinuation of Methimazole Prior to Radioiodine Ablation

The following case involves a 62-year-old female patient suffering from heart failure with reduced ejection fraction (HFrEF) secondary to non-ischemic cardiomyopathy and Graves disease, who developed ventricular fibrillation (VF) after discontinuation of methimazole in preparation for radioiodine ablation. Electrocardiogram (ECG) showed a severely prolonged QTc in the setting of thyrotoxicosis, which significantly improved with high dose methimazole. VF secondary to thyrotoxicosis has rarely been reported and the literature review shows scarce data on its mechanism. Our case demonstrates not only a possible mechanism for the arrhythmia, but also highlights a potential risk factor for it. The report details how discontinuing antithyroid medication leads to VF in our patient and reviews the current literature on antithyroid withdrawal prior to radioiodine ablation therapy. Caution should be taken when discontinuing antithyroid medications in patients with advanced heart failure as potentially lethal ventricular arrhythmias can ensue.

The success rate of radioactive iodine therapy for Graves' disease in iodine-replete area and affecting factors: a single-center study

OBJECTIVE

Initial treatment options for Graves' disease include antithyroid drugs, radioactive iodine (RAI), and surgery. Because of similar effects of three modalities, initial treatment preferences differ by country to country. In Korea, iodine-replete area, RAI was used as a second-line option. For these reasons, the RAI success rate in Korea might differ from other countries.

METHODS

A total of 247 patients were enrolled. The primary outcome was cumulative success rate in the first year, and the secondary outcome was factors that affected the success. Delayed response, which included patients who attained successful RAI during the follow-up, after the first year without further RAI, and factors that affected the delayed response were reviewed.

RESULTS

The cumulative success rate in the first year was 62.8%. Higher RAI activity [odds ratio (OR) 2.56, P = 0.02], longer disease duration (OR 0.43, P = 0.01), larger goiter (OR 0.31, P = 0.01), and higher post-RAI fT4 (fT4 between upper normal limit (UNL) to 1.5 × UNL; OR 0.24; P < 0.01, 1.5 × UNL<; OR 0.08; P < 0.01) were associated with RAI success. Twenty-seven patients showed delayed response, and goiter size (P < 0.05), pre-RAI TSH receptor Ab (TRAb) level (P < 0.01) and post-RAI fT4 (P < 0.01) were associated.

CONCLUSION

The success rate of the first RAI in Korea was lower than that in other countries. Delayed response was observed in patients with smaller goiter, low pre-RAI TRAb, and low post-RAI fT4. In these patients, clinical follow-up with monitoring could be an option, and decision of optimal timing of first RAI is crucial.