A pregnant woman with an autonomously functioning thyroid nodule: a case report

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Background
The epidemiology and natural history of autonomously functioning thyroid nodules (AFTNs) have not been elucidated. Here we report the pregnant Japanese woman with an AFTN.

Case presentation
The patient was a 31-year-old woman who was hospitalized due to the placenta previa associated with threatened abortion at the 16 weeks of her third pregnancy. At her second pregnancy, she was euthyroid but had a single, 2.3 cm nodule on her right thyroid lobe. Her thyroid hormone level was trended increased with her pregnancy progression, and the thyrotoxic state was remained after delivery. Before her third pregnancy, her hyper-vascular nodule enlarged to 3.4 cm at regular monitoring. When she visited our hospital, she was at 16 weeks of pregnancy and had thyrotoxicosis with negative TSH-receptor antibody. She delivered a baby weighing 2615 g without hypothyroidism at 39 weeks of pregnancy by natural delivery. After delivery, a 99mTc scintigram showed a hot spot in her right thyroid lobe. She was diagnosed with AFTN and treated with methimazole while nursing.

Conclusions
This case showed that hCG stimulation during pregnancy caused thyroid nodule enlargement and enhanced thyroid hormone production. The pregnancy could be the pathological stimulus and provides chance to diagnosis for AFTNs.