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Endocrine Abstracts (2023) 91 CB13 | DOI: 10.1530/endoabs.91.CB13

King’s College Hospital, London, United Kingdom

A 28 year old lady presented with a 4 month history of anxiety, palpitations, weight loss and a pressure sensation in the neck. On examination she had fine tremor of her outstretched fingers and no palpable goitre with a regular heart rate. FT4 was 22 pmol/l(10.3-24.5), FT3 7.9 pmol/l(3.5-6.5), TSH 0.02 mIU/l(0.3-5.5), TSH receptor antibodies (TRAb) <0.9 U/l(0-1.75) and TPO antibodies <4 IU/ml (0-35). She was started on Carbimazole 20 mg daily and after being well controlled this was eventually weaned off. She was again referred with clinical and biochemical thyrotoxicosis when 34 weeks pregnant and was treated medically with low dose thionamides. TRAb’s were again undetectable and delivery was uneventful. Anticipating the next planned pregnancy, she was referred for thyroidectomy. Histology showed hyperplastic thyroid follicles consistent with Graves’ disease. Post-surgery she continued to be thyrotoxic on 150 mg of L-thyroxine. She was again referred at 26 weeks gestation with biochemical thyrotoxicosis after having stopped L-thyroxine for 2 weeks, with a suspicion of relapsed Graves’ disease secondary to remnant tissue. TRAbs were again undetectable and there was detectable thyroglobulin 29.8 mg/l(0-40). She was restarted on Carbimazole and thyroid ultrasound showed two possible areas of focal thyroid remnant tissue. Pregnancy was again uneventful. Prior to revision neck surgery, a Tc99 uptake scan showed an ectopic large focus of tracer concentration in the left mediastinum with an uptake of 3.5% (Normal <3%) and at this point an older Tc99 scan from eight years ago which was unavailable to the endocrine team initially, was revisited and demonstrated a toxic right thyroid nodule with suppression elsewhere in the thyroid and a retrosternal focus of uptake. CT showed a rounded soft-tissue density mass in the anterior mediastinum measuring 4 x 6.5 cm. Her case was discussed in the southeast London Network thyroid MDM. The consensus was that this is more likely in keeping with seronegative Graves’ disease and either high dose radioactive iodine therapy or thoracic surgery was advised. The ectopic mediastinal autonomous thyroid tissue was successfully removed with thoracotomy as per patient’s wish. Histology showed nodular hyperplastic thyroid tissue.

Discussion: The coexistence of both Graves’ disease and toxic nodules (Marine-Lenhart syndrome) is uncommon. It is even rarer to see ectopic thyroid tissue in this setting. The diagnosis was further complicated by Graves’ disease being TRAb negative.

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