Hypercalcaemia of malignancy is a common complication for patients with advanced malignancies. Once hypercalcaemia develops, a patient’s prognosis is in the vicinity of months.(1) The three main mechanisms for hypercalcaemia are: excessive PTHrP production, osteolytic metastases and tumour production of 1,25-hihydroxyvitamin D. (2) Current guidelines recommend the use of IV Bisphosphonates and Denosumab as mainstay of management. Calcitonin is only recommended for 48-72 hours in severe hypercalcaemia (>3.5) due to the development of tachyphylaxis. (2,3) We present a case which challenges this recommendation.
An 80-year-old female presented to the ED with lethargy, falls and confusion. Examination was unremarkable and investigations revealed a calcium of 3.55mmol/L. Her history was significant for metastatic uterine sarcoma. She was on Letrozole and Medroxyprogesterone guided by her Oncologist. She was managed with IV fluids and Pamidronate 60mg and discharged with a calcium of 2.52mmol/L. Unfortunately, after two weeks she re-presented with rebound hypercalcaemia and an acute kidney injury. Investigations showed: Calcium 2.94mmol/L (2.15-2.55), Cr 101umol/L (45-90), eGFR 45mL/min/1.73m2 (>90), 1,25-OH vitamin D 246pmol/L (60-200), PTHrP <1 (<1). She was managed with IV Zoledronic acid 4mg and Prednisone 30mg daily given her elevated 1,25-OH vitamin D and her calcium improved to 2.68mmol/L. One week later she re-presented again with confusion and weakness. Her corrected calcium was 3.26mmol/L (2.15-2.55) and she received Denosumab 120mg. She continued high dose Prednisone (15mg-40mg daily), Pamidronate, Zoledronic acid and Denosumab for another 8 weeks. Her calcium continued to rebound and reached 3.76mmol/L despite guideline directed management. She eventually received Calcitonin 100units subcutaneously BD and experienced a rapid and sustained improvement in her Calcium. She has continued Calcitonin continuously for a year. Her most recent calcium was 2.39mmol/L in June 2024.
This case report challenges the conventional teaching that Calcitonin use is limited due to tachyphylaxis in hypercalcaemia of malignancy.