Nadia Osman, Henna Patel, Gadintshware GaoatsweDepartment of endocrinology and diabetes, Newham University Hospital, Barts Health NHS Trust Correspondence: Nadia Osman (n.osman3@nhs.net)

Thyroid Research 2023, 16(S1):PO7

Background and aims: Hypercalcaemia is a common clinical problem. It can occur due to the imbalance between calcium entry into the circulation, deposition in bone and urinary excretion. Primary hyperparathyroidism and malignancy account for more than 90% of these cases1. Excess thyroid hormones, as occurs in hyperthyroidism can impact calcium metabolism and lead to hypercalcaemia in up to 20% of cases1. We describe a case series in which hypercalcaemia occurs alongside concomitant hyperthyroidism. We investigated the effects of antithyroid treatment on serum calcium levels in these patients and review the literature.

Methods: We prospectively followed calcium and thyroid hormone levels following commencement of antithyroid medications in three patients presenting with hyperthyroidism and PTH-independent hypercalcaemia. All 3 patients presented with classical symptoms of hyperthyroidism with a constellation of symptoms including weight loss, palpitations, and heat intolerance.

Results: All were found to be thyrotoxic with positive TSH receptor antibodies confirming Grave’s disease and thyroxine level was above the assay detection level (100pmol/L). All patients also demonstrated PTH-independent hypercalcaemia, with corrected calcium levels ranging between 2.69 to 3.30mmol/L and required admission for intravenous fluid rehydration. Commencement on a combination of Propranolol and Carbimazole resulted in normalisation of calcium and PTH as thyroxine levels improved.

Conclusion: Hypercalcaemia is not uncommon in hyperthyroidism. Thyroid hormones can affect bone metabolism by causing increased bone turnover and accelerated bone remodelling via direct or indirect effects on osteoclast activity2,3. As a result, hypercalcaemia occurs independently of PTH. Multiple cases of hyperthyroidism with hypercalcaemia have been reported. In many of these cases, treatment of hypercalcaemia required calcium lowering therapy including calcitonin and bisphosphonates4. However, our cases demonstrate the normalisation of serum calcium with no adverse outcomes using antithyroid medications alone. This suggests that early identification and treatment of hyperthyroidism with antithyroid medications may be sufficient in uncomplicated hypercalcaemia due to hyperthyroidism.

All patients have been consented for publication of this abstract.

References

1. Shane E. UpToDate. Etiology of hypercalcaemia. Available at: https://www.uptodate.com/contents/etiology-of-hypercalcemia [Accessed 20/3/23].

2. Britto, J. M., Fenton, A. J., Holloway, W. R., & Nicholson, G. C. (1994). Osteoblasts mediate thyroid hormone stimulation of osteoclastic bone resorption. Endocrinology, 134(1),169–76.

3. Pantazi, H., & Papapetrou, P. D. (2000). Changes in parameters of bone and mineral metabolism during therapy for hyperthyroidism. The Journal of clinical endocrinology and metabolism, 85(3), 1099–1106.

4. Chen, K., Xie, Y., Zhao, L., & Mo, Z. (2017). Hyperthyroidism-associated hypercalcemic crisis: A case report and review of the literature. Medicine. 96(4), e6017.