SUN-792 A Case of PTH-Dependent and Independent Hypercalcemia

Abstract Disclosure: K. Khoshbin: None. S. Ahmadi: None. A.K. Sumal: None. Hypercalcemia is a frequently encountered condition in hospitalized patients and can be broadly classified into two major categories: parathyroid hormone (PTH)-dependent and PTH-independent. A thorough evaluation of potential causes is essential before attributing hypercalcemia to a specific etiology.We present the case of a 51-year-old woman with no known medical history, transferred to our hospital following a motor vehicle accident. Laboratory investigations revealed progressively rising calcium levels, prompting consultation with the endocrinology team. Albumin-corrected calcium was 13.0 mg/dL (normal: 8.6–10.4 mg/dL), ionized calcium was 1.78 mmol/L, PTH was elevated at 267 pg/mL (normal: 11–51 pg/mL), 25-hydroxyvitamin D was 11 ng/mL, and 1,25-dihydroxy vitamin D was 87 pg/mL (normal: 19.9–79.3 pg/mL). PTH-related peptide was <2 pmol/L (normal: 0–2.3 pmol/L), phosphorus was 1.4 mg/dL, and TSH and serum protein electrophoresis were within normal limits.The patient was started on intravenous fluids, calcitonin, and cinacalcet for presumed PTH-dependent hypercalcemia secondary to primary hyperparathyroidism. Neck ultrasound revealed an 11-mm oval hypoechoic nodule inferior to the left thyroid lobe, suggestive of a parathyroid lesion. CT imaging did not reveal any suspicious parathyroid adenoma in the neck or mediastinum but identified mediastinal and hilar lymphadenopathy. Flow cytometry excluded lymphoma, angiotensin converting enzyme (ACE) level and infectious disease testing, including QuantiFERON and tests for endemic mycoses were unremarkable. Bronchoscopy with lymph node biopsy demonstrated non-necrotizing granulomatous inflammation, with negative gram stain and cultures confirming a diagnosis of sarcoidosis. Prednisone therapy was initiated for sarcoidosis-associated hypercalcemia.She was evaluated by endocrine surgery for parathyroidectomy; however, surgery was deferred due to her recent stroke. As a result, the patient received zoledronic acid and prednisone for hypercalcemia management and continued cinacalcet after discharge. This case is unique because it demonstrates two different etiologies of hypercalcemia – namely primary hyperparathyroidism and sarcoidosis – within the same patient. It underscores the importance of considering alternative etiologies for hypercalcemia when other clues exist on laboratory or other investigations, particularly when initial findings suggest a complex interplay of conditions. An intriguing aspect of this case is that despite the diagnosis of sarcoidosis, the patient’s 1,25-dihydroxyvitamin D levels were not elevated. This may be attributed to a deficiency in the substrate (25-hydroxyvitamin D) due to coexisting vitamin D deficiency. Thus, this case highlights the diagnostic challenges in hypercalcemia and the need for comprehensive evaluation. Presentation: Sunday, July 13, 2025