Abstract: PUB099
Severe Hypercalcemia by PTH-independent Extrarenal Production of 1,25-Hydroxyvitamin D
Session Information
Category: Bone and Mineral Metabolism
- 502 Bone and Mineral Metabolism: Clinical
Authors
- Patel, Ravi S., Methodist Dallas Medical Center, Dallas, Texas, United States
- Collazo-Maldonado, Roberto L., Methodist Dallas Medical Center, Dallas, Texas, United States
- Patel, Avani R., Meharry Medical College School of Medicine, Nashville, Tennessee, United States
- Rosario Aulet, Alexandra, Methodist Dallas Medical Center, Dallas, Texas, United States
Introduction
Humoral hypercalcemia of malignancy is a condition characterized by elevated serum calcium levels due to exogenous production of parathyroid hormone-related protein (PTHrP). However, in rare cases, PTHrP may be normal and elevated serum calcium can be secondary to increased 1,25 hydroxy vitamin D production. Hypercalcemia of malignancy due to increased 1,25 hydroxy Vitamin D production can be challenging to diagnose due to its infrequency, but it may help discern the underlying cause of hypercalcemia.
Case Description
An 82 yo Hispanic woman presented to the ED due to confusion and generalized weakness. A clinical diagnosis of severe hypercalcemia with acute metabolic encephalopathy was made as her serum calcium levels were >14 mg/dl and creatinine 1.29 mg/dl on admission. She was recently diagnosed with Non-Hodgkin lymphoma (NHL) with metastasis to her liver and lungs. Her parathyroid hormone level was 12.4 pg/ml and parathyroid hormone-related protein level was <2.0 pmol/L. The patient’s 1,25 hydroxy vitamin D levels, which resulted later, were markedly elevated at 186. The patient was treated with aggressive volume expansion, calcitonin, zoledronic acid, and steroids resulting in a quick improvement in her calcium levels and mentation. The patient was discharged in stable condition with a calcium level of 10.8 mg/dl with an improvement in kidney function with follow up with oncology.
Discussion
In patients with NHL, the most common cause of hypercalcemia (accounting for up to 80%) is the secretion of PTHrP, known as humoral hypercalcemia of malignancy. However, in rare cases, elevated levels of 1,25 hydroxy vitamin D can also cause hypercalcemia of malignancy despite normal PTHrP levels due to increased a1 hydroxylase activity by macrophages and lymphocytes.