Endocrine Abstracts

Background Disturbances of calcium metabolism are frequent in patients with untreated hyperthyroidism, however they are typically mild and asymptomatic (1).

Methods We describe a case of a 56-year-old female who presented with severe, symptomatic hypercalcaemia and hyperthyroidism secondary to Grave's disease. She initially presented with symptoms of weight loss, generalised malaise and lethargy. Investigations revealed hyperthyroidism and a positive TSH receptor antibody at 17.0 U/l (Reference range 0.0-2.0 U/l). The maximum calcium level measured was 3.27 mmol/l (Reference range 2.20-2.70 mmol/l). Treatment was initiated as an inpatient with intravenous fluids and treatment for hyperthyroidism was initiated concurrently with carbimazole. Parathyroid hormone levels were suppressed <5.0 pg/ml (Reference range 10.0-65.0 pg/ml). Investigations for an alternative cause of hypercalcaemia were negative. She responded to therapy with complete resolution of hypercalcaemia and symptoms of hyperthyroidism.

Conclusions Thyrotoxicosis is a recognised cause of hypercalcaemia. Most studies have demonstrated increases in mean calcium, phosphate and alkaline phosphatase levels and decreases in magnesium and albumin levels in pateints with hyperthyroidism. The mechanism by which hyperthyroidism causes hypercalcaemia is suggested by the literature to be a direct effect of thyroid hormone primarily on bone metabolism. With treatment of hyperthyroidism, there is a reversal of the metabolic abnormalities towards normal. Whilst hypercalcaemia can commonly occur, it is unusual for it to be severe and symptomatic. In many of the cases with severe hypercalcaemia described, another cause has been identified. We present a case of severe hypercalcaemia caused by hyperthyroidism with the one of highest measured calcium we could identify in the literature.

Reference

(1) Daly JG, Greenwood RM, Himsworth RL. Serum calcium concentration in hyperthyroidism at diagnosis and after treatment. Clin Endocrinol (Oxf) 1983; 397-404