https://orcid.org/0000-0002-0744-3942
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A 70-year-old female presented with hyperthyroidism from Graves disease (GD) had positive thyrotropin receptor antibodies (TRAb) (3.78 IU/L, normal <0.55 IU/L) and high thyroid radioactive iodine uptake on a 24-hour test with diffuse distribution (Fig. 1A) [1]. Thyroid ultrasound showed a 0.6-cm cystic-solid isoechoic nodule in the right lobe. After 36 months on methimazole, thyroid function normalized with TRAb persistently <0.55 IU/L. Six months after stopping methimazole, the patient relapsed with thyrotropin <0.01 mIU/L (reference range [RR], 0.27-4.2 mIU/L), normal free thyroxine 1.27 ng/dL (16.3 pmol/L) (RR, 0.9-1.7 ng/dL; 11.9-21.8 pmol/L), normal triiodothyronine 89 ng/dL (1.4 nmol/L) (RR, 60-180 ng/dL; 0.9-2.8 nmol/L), and undetectable TRAb. Radioactive iodine scan revealed a solitary “hot” nodule in the right lobe, which changed the diagnosis to solitary toxic thyroid nodule instead of GD (Fig. 1B) [1]. Ultrasound confirmed a 1.8 × 1.0 × 0.9-cm cystic-solid isoechoic nodule (Fig. 1C). The patient was treated with iodine-131 (1.11 MBq; 30 mCi), leading to successful treatment that was confirmed by follow-up scintigraphy showing homogeneous diffuse distribution (Fig. 1D). Marine-Lenhart syndrome was considered, but scintigraphy lacked the typical diffusely increased activity in both parenchyma and affected nodules [2]. This case highlights the importance of thyroid scintigraphy in differentiating between GD and toxic nodular goiter, particularly when TRAb is negative and nodules are present, guiding appropriate treatment decisions.
Cross indicates the patient' suprasternal notch. (A) 24-hour thyroid radioactive iodine test revealed high uptake (57%; normal reference: 8%-32%) and a diffuse distribution, strengthening the diagnosis of Graves disease. (B) A 24-hour thyroid radioactive iodine test showed high uptake of 36% and a solitary “hot” thyroid nodule in the right lobe, supporting the diagnosis of solitary toxic thyroid nodule. (C) Thyroid ultrasound revealed 1 cystic-solid isoechoic nodule in the right lobe, measuring 1.8 × 1.0 × 0.9 cm, reinforcing the diagnosis of toxic thyroid nodule. (D) A 24-hour thyroid radioactive iodine scan after iodine-131 treatment with 1.11 MBq (30 mCi) showed a homogeneous diffuse thyroid distribution, demonstrating a successful treatment of the solitary toxic thyroid nodule.
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