A Case of Hypercalcaemia With Suppressed Parathyroid Hormone in a Middle-Aged Female: Diagnostic Challenge and Association With Hyperthyroidism.

Hypercalcaemia with suppressed parathyroid hormone (PTH) typically raises concern for malignancy-related, granulomatous disorder-related or drug-related hypercalcaemia but can occasionally be caused by less common conditions. We present the case of a middle-aged female with hypercalcaemia with reduced PTH levels despite vitamin insufficiency, who was eventually diagnosed with autoimmune hyperthyroidism. The diagnostic challenge arose from the atypical association of hyperthyroidism and hypercalcaemia. This case highlights the importance of considering hyperthyroidism in the differential diagnosis of hypercalcaemia.