Endocrine Abstracts

Case History: A 46 year old lady presented with deranged thyroid function (TSH 0.05, T4 19.7). She reported palpitations, mild eye irritation, sweats and weight loss. Examination revealed a resting tremor and regular pulse (72 bpm). A small goitre with bruit was present, but no evidence of thyroid eye disease. Block-and-replace regime of carbimazole and levothyroxine was commenced for Graves’ disease. Thyroid peroxidase antibodies were <1. After one year of euthyroidism treatment was stopped, but she relapsed into hyperthyroidism. The patient opted for total thyroidectomy. The histology report was ‘consistent with treated Graves’ disease.’ Four days following surgery she developed palpitations and tremor; blood tests confirmed hyperthyroidism.

Investigations: Ultrasound of the neck confirmed total thyroidectomy with no residual thyroid tissue. Thyroid uptake with SPECT CT and I131 scan of the thyroid area were unremarkable. The elusive source of thyroid hormone prompted consideration of ectopic production. Pelvic ultrasound revealed a ‘complex mixed cystic/solid mass, ovarian in origin’. TSH receptor antibodies were negative, but CA125 elevated at 76.9. I131 scan of the abdomen and pelvis demonstrated 2 foci of uptake- in the bladder and the left ovary.

Results and treatment: Histology from unilateral salpingo-oopherectomy and omental washings demonstrated follicular thyroid carcinoma arising in struma ovarii. Levothyroxine re-commenced after surgery achieved euthyroidism. Thyroglobulin was <5 with no histological evidence of intraepithelial invasive neoplasia, so adjuvant therapy was not necessary.

Conclusions and points for discussion: Struma ovarii is a specialised or monodermal teratoma with thyroid tissue comprising more than 50% of the overall tissue. It accounts for 5% of all ovarian teratomas. Whilst approximately 95% are benign, malignant transformation can occur, most commonly papillary carcinoma, followed by follicular carcinoma. The majority of struma ovarii are asymptomatic however 5–8% present with hyperthyroidism. Our patient presented with hyperthyroidism which was treated as presumed antibody-negative Graves’ disease. Patient preference for total thyroidectomy, rather than radioiodine, meant a thyroid uptake scan was not performed which would have demonstrated low thyroid uptake prompting investigation for ectopic hormone production. Thyroid histology supported a diagnosis of Graves’, however clinical history may have affected interpretation. Initial I131 scan was limited to the neck and thorax thus missing the struma ovarii. Whilst some malignant struma ovarii cause abdominal signs (ascites, abdominal swelling) our patient had no localising features. This case demonstrates the need to suspect rare causes of excess thyroid hormone production in antibody-negative hyperthyroidism.