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.