Atypical Calcitriol-Mediated Hypercalcemia in Late Life: A Hypothesis-Generating Case.

Calcitriol-mediated hypercalcemia is most commonly associated with granulomatous disease or lymphoma and rarely occurs without an identifiable cause. We present the case of a 96-year-old woman who developed severe symptomatic hypercalcemia with elevated 1,25-dihydroxyvitamin D (calcitriol), low 25-hydroxyvitamin D (calcidiol), suppressed parathyroid hormone, and no evidence of malignancy, granulomatous disease, endocrine dysfunction, or vitamin D intoxication. She improved with intravenous fluids, calcitonin, and corticosteroids. We hypothesize that age-related impairment of the fibroblast growth factor 23-Klotho regulatory axis contributes to the dysregulation of calcitriol synthesis. This case highlights diagnostic challenges in elderly patients with hypercalcemia and raises the possibility of age-related mineral metabolism dysregulation as an underrecognized contributor to idiopathic calcitriol-induced hypercalcemia.