Endocrine Abstracts

Case History :A 34-year-old Caucasian female patient presented in May 2015 to A&E with symptoms of overt thyroid dysfunction. She was managed medically until June 2016 when thionamide treatment was withdrawn. Unfortunately, this lady had a first disease relapse in July 2018 whilst she was pregnant at 35 weeks of gestation and then further disease relapse in January 2020 during her second pregnancy.

Investigations: Initial biochemistry in 2015 confirmed thyrotoxicosis – TSH: < 0.01 mIU/l, fT4: 22 pmol/l and fT3: 7.9 pmol/l. TRAb titre was undetectable. A⁹⁹ Technitium uptake scan was at the time normal. Despite initial good response to medical treatment, in June 2018 during 3^rd trimester of her pregnancy, this lady developed again symptoms of thyroid dysfunction. Repeat biochemistry confirmed thyrotoxicosis relapse with TSH: <0.01 mIU/l, fT4: 27.1 pmol/l and fT3: 12.1 pmol/l. Below are illustrated thyroid function tests at initial presentation and during relapses.

Treatment: At diagnosis in 2015, Carbimazole 20 mg daily was offered for 12 months and once this lady achieved remission, treatment was withdrawn. During first relapse, it was felt that Carbimazole was the best option as she was at the end of pregnancy. This lady continued following delivery, albeit using just 5mg daily as she was breastfeeding. Definite treatment was discussed, and total thyroidectomy was considered optimal as this lady was breastfeeding and was planning to conceive again imminently. She had total thyroidectomy in October 2019. Histology was consistent with Grave’s disease and focal nodular hyperplasia. Surprisingly, she became thyrotoxic after surgery which initially was thought to be due to factitious thyrotoxicosis. She was again pregnant at 27 weeks of gestation. Despite thyroxine withdrawal, clinical and biochemical thyrotoxicosis persisted and thionamide treatment was restarted. This lady was referred for a new⁹⁹ Technitium uptake scan which demonstrated a large focus of tracer concentration in the left anterior mediastinum accumulating 3.5% of the administered activity. It retrospectively transpired that the 2015 uptake scan had demonstrated the same mediastinal focus. Cross-sectional imaging with CT showed a large anterior mediastinal mass, compatible with thyroid gland tissue.

Conclusion: Ectopic thyroid tissue is a rare entity resulting from developmental defects at early stages of thyroid gland embryogenesis. Ectopic Graves’ disease is exceedingly rare and differentiating from eutopic disease can represent a diagnostic conundrum.