Objective: Hypercalcemia in patients with acromegaly is rare and usually due to co-existent primary hyperparathyroidism. The etiology of hypercalcemia directly related to acromegaly is debated.
Methods: We present a case report of 1,25(OH)2D3-mediated hypercalcemia in a patient with acromegaly and discuss potential pathophysiological mechanisms contributing to the development of hypercalcemia late in the course of the disease.
Results: A 67-year-old female presented with classical features of acromegaly. A review of her previous photographs suggested a disease duration of approximately 10 years, and her serum calcium (Ca) was normal during this period. A biochemical work up confirmed a combined growth hormone (GH-) and prolactin (PRL-) cosecreting tumor with a GH level of 92.03 ng/mL (normal 0-3.61), an insulin-like growth factor-1 (IGF-1) level of 1,498 ng/mL (59-225), and a PRL level of 223.3 ng/mL (2-17.4). Magnetic resonance imaging (MRI) of the pituitary showed a 1.9-cm macroadenoma. Her preoperative work up revealed new onset hypercalcemia with a corrected serum Ca level of 10.7 mg/dL (8.5-10.5), an ionized Ca level of 1.37 mmol/L (1.08-1.30), a parathyroid hormone (PTH) level of 13.0 pg/mL (10-60), and a high 1,25(OH)2D3 level of 72.6 pg/mL (15-60). She underwent resection of the pituitary adenoma with normalization of GH and PRL levels, and her IGF-1 level decreased to 304 ng/mL. Her serum Ca (9.3 mg/dL), ionized Ca(1.22) and 1,25(OH)2D3 levels (38.6 pg/mL) normalized after surgery.
Conclusion: While overt hypercalcemia in acromegaly is rare, it tends to occur late in the disease course. The hypercalcemia is mediated by elevated 1,25(OH)2D3 levels rather than PTH.