GRAVES' DISEASE IN ECTOPIC THYROID TISSUE: A SCOPING REVIEW AND A CASE STUDY.

Background: Persistent Graves' disease (GD) after total thyroidectomy is sporadic and may be explained by incomplete total thyroidectomy, GD in ectopic thyroid tissue (ETT) or struma ovarii.

Methods: We present a novel case of ectopic GD in a giant paracardiac mass, including an in-depth histologic exam. We searched the Pubmed database on GD in ETT.

Results: A 34-year-old woman presented with severe thyrotoxicosis, 4 months after total thyroidectomy, and 6 weeks after cessation of levothyroxine substitution. Persistently high thyrotropin receptor antibodies (TSH-R-Ab) (27 IU/l, normal <1.5 IU/l) and thyroglobulin > 5000 µg/l (normal <77 µg/l) suggested GD in ETT. A 99mTc-pertechnetate SPECT/CT scan showed uptake in a paracardiac mass. After surgical removal of the 13 cm paracardiac mass, euthyroidism was achieved. Histology was typically remarkable for a Graves' pattern in the ETT as opposed to a nodular pattern in the eutopic thyroid. The additional scoping review encompasses 29 reported ETT cases of which only 11 were in the mediastinum. Graves' eye disease was present in 11 / 29 subjects.

Conclusion: This is the first report showing a markedly different histology between the thyroid and the ectopic tissue. Persistent systemic severe GD post-thyroidectomy led to the detection of a giant paracardiac ectopic thyroid. GD in ETT is rare and presents a diagnostic challenge.