Endocrine Abstracts

Background: Hyperthyroidism can cause mild-to-moderate hypercalcemia due to parathyroid (PTH)-independent increase in bone turnover. Whether people predisposed to primary hyperparathyroidism are more likely to manifest hyperthyroidism-induced hypercalcaemia is unknown. We report a case of primary hyperparathyroidism diagnosed a decade after an initial presentation with Graves’ disease associated with transient PTH-independent hypercalcaemia.

Case presentation: A 50-year-old woman was admitted to the hospital with a 10-week history of weight loss, lethargy, palpitation and polydipsia. TSH was undetectable, freeT4 >100.0 pmol/l and corrected calcium 3.03 mmol/l. Further investigations showed low PTH at 12 ng/l (≈1.27 pmol/l); thyroid peroxidase and TSH receptor antibody titres were raised. After initial rehydration and commencement of antithyroid therapy with Carbimazole, the acute hypercalcaemia resolved. She eventually underwent total thyroidectomy for recurrent Graves’ hyperthyroidism 5 years after the initial presentation and was treated with lifelong levothyroxine therapy. Eleven years after the initial presentation, she re-presented with hypercalcaemia (levels ranging from 2.62 to 2.89 mmol/l). PTH was raised (ranging from 10.1 to 12.5 pmol/l). The urinary calcium excretion index was raised to 0.072 mmol/l. Subsequent investigations identified an enlarged right inferior parathyroid adenoma in the postoperative thyroid bed and osteoporosis. She underwent unilateral right inferior parathyroidectomy with a successful biochemical cure of primary hyperparathyroidism.

Discussion: This case demonstrates the uncommon presentation of PTH-independent hypercalcemia due to Graves’ hyperthyroidism, followed years later by PTH-dependent hypercalcemia due to primary hyperparathyroidism. The metachronous presentations of these hypercalcaemic pathologies may reflect a random occurrence or yet unrecognised shared predispositions.