An Interesting Case of Vitamin D-Mediated Severe Hypercalcemia in a Patient With Renal Mass.

Hypercalcemia of malignancy (HCM) is the most common cause of hypercalcemia in hospitalized patients. The pathogenesis of HCM is often multifactorial. One of the rare causes of HCM is extra-renal production of 1,25-dihydroxyvitamin D (or calcitriol), which is often seen in patients with lymphoproliferative malignancies. Here we report an interesting case of a 77-year-old female with severe hypercalcemia and renal mass. Initially, she was presumed to have humoral hypercalcemia of malignancy. However, her renal mass turned out to be diffuse large B cell lymphoma upon removal. Her severe hypercalcemia was attributed to a combination of ectopic calcitriol production from the tumor and probable iatrogenic vitamin D intoxication. This case highlights the need to consider multiple concurrent etiologies in patients with severe hypercalcemia.