Endocrine Abstracts

Ectopic Graves’ disease and sustained thyrotoxicosis after total thyroidectomy are extremely rare. In this abstract, we report a case of a 34-year-old female, presenting at our department for persistent Graves’ disease (GD) despite total thyroidectomy performed at an affiliated hospital 4 months earlier and cessation of thyroid hormone replacement 6 weeks before presentation. She complained of palpitations, nervousness and sweating. Her pulse rate was 82/min, while on propranolol 20 mg td. Free T4 was 65 pmol/l (reference range 12-22 pmol/l), free T3 35 pmol/l (3.1-6.8 pmol/l), TSH <0.005 mU/l (0.3-4.2 mU/l) and TSH receptor antibodies (TSH-R-Ab) 27 IU/l (cut-off <1.5 IU/l, (Elecsys®, Roche Cobas)). Persistent GD in a giant paracardial thyroid was diagnosed by 99mTc-pertechnetate SPECT/CT. In the neck, only subtle pertechnetate uptake was found, while neck ultrasound showed no residual thyroid tissue. Euthyroidism was achieved on antithyroid treatment with methimazole 60 mg/day and methylprednisolone 32 mg (oral) followed by surgical removal of the large ectopic thyroid mass. At thoracotomy, a 13 X 10 X 5.5 cm lesion attached to the pericardium was resected. Nevertheless, binding TSH-R-Ab remained high (21.7 IU/l) and the patient developed active moderate-to-severe Graves’ orbitopathy 3 months after mediastinal surgery, requiring IV methylprednisolone according to the 2021 Eugogo guidelines. Currently (1 year and 9 months after mediastinal surgery), she is euthyroid on levothyroxine 100 µg daily (free T4 23.1 pmol/l, free T3 5.6 pmol/l, TSH 0.05 mU/l), while binding TSH-R-Ab remain high (34 IU/l). Serial measurement of the stimulatory TSH-R-Ab, at the accredited and certified JGU thyroid lab, with the help of a novel, CE-marked, ultrasensitive cell-based bioassay (cut-off < 0.024 IU/l) demonstrated the sustained presence of a high concentration of these specific TSH-R-Ab in the patient serum post-thyroidectomy and post-thoracotomy (3.72 IU/l and 3.62 IU/l in December 2023 and March 2024, respectively). Multiple blocks of the eutopic thyroid (35 g) and the large ectopic tissue (408 g) were examined histologically. The eutopic thyroid showed signs of hyperplasia within a nodular structure with variable follicle size. In contrast, the ectopic tissue showed a more diffuse pattern with higher epithelial cells, which is typical for GD. Molecular testing of the giant ectopic tumor (PAX-PPARgamma, BRAF, RET, etc.) was negative for mutations. In conclusion, we present a rare case of persistent GD in a giant ectopic paracardial ectopy, providing to our knowledge the first description of markedly different histological appearance of eutopic versus ectopic tissue in the context of GD.