Severe Refractory Hypocalcemia in a Patient with Metastatic Prostate Carcinoma Following Denosumab Injection

An 86-year-old male with a history of metastatic castrate sensitive prostate cancer received a single dose of Denosumab for his bony metastases. Two weeks later, he presented to the hospital due to left foot cellulitis and was incidentally found to have profound hypocalcemia whereas his serum calcium was normal at the time of Denosumab injection. A thorough workup was undertaken which showed severe Vitamin D deficiency. He was diagnosed with Denosumab induced hypocalcemia with underlying Vitamin D deficiency which was refractory to supplemental calcium and Vitamin D. This case demonstrates the potential of Denosumab to cause profound hypocalcemia which can be resistant to therapy. Bone metastasis is a common clinical encounter and Denosumab is an effective therapy to prevent skeletal related events (SRE). Therefore, given its widespread use, it is extremely important to identify and treat risk factors that may aggravate hypocalcemia when treated with Denosumab.