6539 Hungry Bone Syndrome & Osteoblastic Metastasis In The Setting Of Prostate Cancer : A Rare Cause Of Hypocalcemia

Abstract Disclosure: B. Sharma: None. M. Khan: None. A. Rao: None. P. Guido: None. Background: Hungry bone syndrome (HBS) is due to excessive calcium and phosphorus sequestration in the bone, manifesting as hypocalcemia and hypophosphatemia.It is most commonly seen as a postoperative complication of parathyroidectomy.Advanced prostate cancer with osseous metastasis has been previously described as is a rare cause of HBS. Clinical Case: A 65 year old male was admitted to the hospital with acute congestive heart failure and severe hypocalcemia.He exhibited symptoms of muscle spasms and perioral paraesthesias. Physical exam was positive for Trousseau's sign.Initial tests were consistent with severe hypocalcemia (corrected non-ionized calcium 6.8 [8.8-10.2] mg/dL), low ionized calcium (0.58 [1.10-1.30] mmol/L). Three weeks prior to admission, corrected non-ionized calcium was 9.8 mg/mL. Other labs showed normal magnesium, normal phosphorus, elevated alkaline phosphatase (1044 [45-117] U/L), low Vitamin D (12 [>30] ng/mL ), elevated iPTH (567 [19-88] pg/mL) and low PTH-rp (9 [11-20] pg/mL]. His electrocardiogram showed regular rate and rhythm with Qtc prolongation (497 ms).He had a significant oncological history of prostate cancer and multiple myeloma in remission.He was previously treated with zoledronic acid, discontinued 1 year prior to admission, for reducing skeletal complications while being treated for multiple myeloma. He had a recent workup with medical oncology for recurrence of prostate cancer due to elevated Prostate-specific antigen (380 [<4.00] ng/mL).Computed tomography imaging showed diffuse osteoblastic metastatic disease in the axial skeleton, pelvis and proximal femur. During hospital admission hypocalcemia was persistent, likely also due to concurrent furosemide use, necessitating the administration of intravenous calcium infusion and use of cholecalciferol and calcitriol.He was discharged on calcium carbonate 4500 mg twice a day, cholecalciferol 50 000 units weekly for 12 weeks and calcitriol 2 mcg twice a day. Conclusion: Hypocalcemia in the setting of prostate cancer is most commonly due to the use of bisphosphonates or Receptor activator of nuclear factor kappa-B ligand (RANK-L) inhibitors. Hypocalcemia in this case was due to sequestration of calcium in the bone by osteoblastic metastasis. This case illustrates the importance of recognising osteoblastic metastasis as a differential in protracted and severe hypocalcemia in malignancy.High doses of calcium, vitamin D, and calcitriol replacement are often needed as the hypocalcemia is usually severe and refractory with some cases requiring prolonged IV calcium infusion.Treatment of the underlying cancer and bone metastases with chemotherapy has been shown to improve hypocalcemia and reduce the requirement of calcium and vitamin D supplementation.There is limited data to suggest if bisphosphonates can be safely used in these cases for prevention of skeletal related events. Presentation: 6/1/2024