# Idiopathic Hypoparathyroidism in an Osteoporosis Patient Receiving Denosumab Therapy

## TL;DR

A 71-year-old woman on denosumab for osteoporosis developed hypocalcemia and low PTH, suggesting idiopathic hypoparathyroidism unmasked by the drug.

## Contribution

This case report highlights a rare side effect of denosumab potentially unmasking idiopathic hypoparathyroidism.

## Key findings

- Denosumab may unmask idiopathic hypoparathyroidism by suppressing bone resorption.
- Calcium supplementation stabilized levels, but PTH remained suppressed.
- The case underscores the need to monitor calcium before denosumab administration.

## Abstract

Idiopathic hypoparathyroidism is a rare endocrine disorder characterized by impaired parathyroid hormone (PTH) secretion leading to hypocalcemia and hyperphosphatemia. We report the case of a 71-year-old female patient receiving denosumab for osteoporosis who was found to have asymptomatic hypocalcemia prior to her fifth denosumab injection. Lab results revealed a low ionized calcium level of 4.45 mg/dL, a low normal total calcium level of 8.2 mg/dL, and an inappropriately low PTH level of 17 pg/mL, with normal magnesium and vitamin D levels. Calcium levels were normal during the previous four doses. With no history of neck surgery, renal disease, autoimmune disease, or malabsorption, a diagnosis of idiopathic hypoparathyroidism was supported, likely unmasked by denosumab-associated suppression of bone resorption. Denosumab treatment was withheld, and calcium carbonate and calcitriol supplementation led to stabilization of serum calcium in the low-normal range, but PTH levels remained suppressed. Our case highlights the importance of ensuring normal calcium levels before denosumab administration and emphasizes the challenges of osteoporosis management in patients with hypoparathyroidism. In this area of treatment, evidence-based data remains limited.