Marked Parathyroid Hormone (PTH)-Independent Hypercalcemia Revealing Sarcoidosis Mimicking Malignancy: A Case Report

Severe hypercalcemia is a life-threatening emergency and requires prompt management. Sarcoidosis is a multisystem granulomatous disease that often involves the lungs but may also involve other systems, leading to extrapulmonary manifestations. The presence of lymphadenopathy, constitutional symptoms, and renal dysfunction can mimic that of malignancy, giving rise to diagnostic uncertainty in some cases. Here we present a 57-year-old male who came with complaints of fatigue, nausea, and right flank pain. Laboratory investigations revealed clinically significant hypercalcemia (13.8 mg/dL) with acute kidney injury (blood urea nitrogen (BUN) 26 mg/dL, serum Cr 2.9 mg/dL) and normal parathyroid hormone (PTH), 30.1 pg/mL. The initial imaging raised the suspicion of malignancy due to the presence of diffuse intra-abdominal and mediastinal lymphadenopathy and splenomegaly. Additionally, there were elevated 1,25-dihydroxyvitamin D and angiotensin-converting enzyme levels with normal PTH-related peptide levels. Bone marrow biopsy gave the picture of extensive non-necrotizing granulomatous inflammation without evidence of lymphoma or leukemia, narrowing the diagnosis towards sarcoidosis. Following treatment with intravenous hydration, zoledronic acid, and subsequent corticosteroid therapy after exclusion of alternative causes of hypercalcemia, calcium levels and renal function returned to baseline. This case highlights the need to consider sarcoidosis as a differential diagnosis in patients with hypercalcemia and normal PTH levels. To avoid misdiagnosis and to allow prompt treatment, a structured diagnostic method with timely histopathological confirmation is needed.