MON-LB66 Altered Mental Status and Hypercalcemia: A Rare Presentation of Pure Osteolytic Metastatic Prostate Cancer

Background: We present a rare case of hypercalcemia with the concomitant presence of parathyroid adenoma, secondary hyperparathyroidism due to kidney disease and hypercalcemia of malignancy. Mild hypercalcemia due to primary hyperparathyroidism often precedes the acute, more severe hypercalcemia of malignancy. Prostate cancers are usually known to cause osteoblastic lesions. We present a rare case of prostate cancer with pure osteolytic metastasis. Case: 73 year old male with past history of ESRD on hemodialysis was brought to the ER with change in mental status. Labs showed elevated serum calcium 13.3 mg/dl (8.6-10.2 mg/dl) and creatinine 7.0 mg/dl (0.60-1.30mg/dl). Patient underwent emergent hemodialysis. Additional lab work revealed, elevated phosphorus level of 5.8mg/dl (2.5-5 mg/dl), low vitamin D 25-hydroxy of 22 ng/ml (30-100 ng/ml) and vitamin 1-25 dihydroxy level of 7 ng/ml (20-79 ng/ml). Both PTH 172.6 pg/ml (12-88 pg/ml) and PTHrP 64 pg/ml (14-27 pg/dl) levels were elevated. Parathyroid scan showed increased uptake in left inferior parathyroid gland indicating the presence of a parathyroid adenoma. Serum calcium levels remained persistently elevated despite being continued on dialysis with a low calcium bath and receiving calcium lowering therapy with calcium binding agent- cinacalcet, calcitonin, bisphosphonate. Further work up for refractory hypercalcemia revealed an elevated prostate-specific antigen (PSA) level of 1420 ng/ml (0-3.999 ng/ml). Bone scan showed no evidence of osseous metastasis. CT abdomen & pelvis showed extensive lytic bony metastases, with metastasis to lung and lymph nodes in mesenteric root and in the pelvis. Prostate gland showed asymmetric contour along the left posterolateral zone suspicious for malignancy with extracapsular spread.Biopsy from the left iliac lytic bone lesion was done that showed poorly differentiated metastatic adenocarcinoma, consistent with a prostatic primary. The patient was started on treatment with anti-androgen medication- Bicalutamide and prednisone and was planned to be started on Leuprolide as outpatient. Discussion: Hypercalcemia is uncommon in advanced prostate cancer compared to other malignancies where osteolytic metastasis is more common than osteoblastic metastasis. Incidence of malignancy in patients with primary hyperparathyroidism and vice-versa is high, hence serum PTH and PTHrP should be measured in hypercalcemic patients with malignancy. If PTHrP and PTH are both elevated, it indicates co-existent primary hyperparathyroidism. Prostate cancers are usually known to cause osteoblastic lesions and pure osteolytic metastasis from prostate carcinoma is extremely rare. Radio-nucleotide bone scan preferentially detects osteoblastic metastasis. CT or MRI is indicated to look for osteolytic lesions if suspicion for bone metastasis is high.