title: A rare cause of hyperthyroidism: functioning thyroid metastases.
abstract: Hyperthyroidism is a common medical problem that is readily treated with antithyroid medications. However, attributing the correct aetiology of hyperthyroidism alters management and outcome. We present a case of a 66-year-old woman with a seemingly common problem of hyperthyroidism associated with a goitre, which was initially attributed to a toxic nodule. However, Tc-99m pertechnetate uptake scan and thyroid-stimulating hormone receptor antibody were negative, inconsistent with a toxic nodule or Grave's disease. Her thyroid function tests proved difficult to control over the next few months. She eventually proceeded to a total thyroidectomy and histology revealed follicular variant papillary thyroid carcinoma. She was started on levothyroxine postoperatively but developed severe hyperthyroidism, revealing the cause of hyperthyroidism to be autonomously functioning thyroid metastases. Although functioning thyroid metastases are very rare, they need to be considered among the differential diagnoses of hyperthyroidism, as there are nuances in management that could alter the eventual outcome.
authors.affiliation: Department of Endocrinology, Singapore General Hospital, Singapore, Singapore.
authors.forename: Daphne
authors.initials: D
authors.lastname: Gardner
authors.affiliation: Mt Elizabeth Medical Centre, Singapore, Singapore.
authors.forename: Su Chin
authors.initials: SC
authors.lastname: Ho
mesh_terms: D000368:Aged; D018265:Carcinoma, Papillary, Follicular / Q000150:complications / Q000473:pathology*; D005260:Female; D006044:Goiter, Nodular / Q000175:diagnosis; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis* / Q000209:etiology; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000473:pathology* / Q000601:surgery; D013964:Thyroid Neoplasms / Q000473:pathology*; D016606:Thyroid Nodule / Q000175:diagnosis; D013965:Thyroidectomy