Clinical Significance of Vitamin D Deficiency in Primary Hyperparathyroidism, and Safety of Vitamin D Therapy

Nasser Mikhail, MD, MSc

Disclosures

South Med J. 2011;104(1):29-33. 

In This Article

Abstract and Introduction

Abstract

Vitamin D deficiency occurs more frequently in patients with primary hyperparathyroidism (PHPT) compared with the general population, and is usually associated with an aggravated form of the disease. Current guidelines recommend measurement of serum levels of 25-hydroxy vitamin D (25-OHD) in all patients with PHPT, and their repletion if the levels are less than 50 mmol/L (20 ng/mL). Limited data suggest that vitamin D treatment is generally safe in subjects with mild PHPT and coexisting vitamin D deficiency. Adverse effects include hypercalcuria and, less commonly, exacerbation of hypercalcemia. Well-designed trials are needed to evaluate the safety of vitamin D replacement therapy in a wide spectrum of patients with concomitant PHPT and vitamin D deficiency. These trials should address the impact of such therapy on the complications and course of PHPT.

Introduction

The panel of the Third International Workshop on Asymptomatic Primary Hyperparathyroidism recently recommended measurement of serum concentrations of 25-hydroxy vitamin D (25-OHD)—the best available test of vitamin D nutritional status—in all patients with suspected primary hyperparathyroidism (PHPT), and initiation of vitamin D supplementation in patients with levels below 20 ng/mL before making any medical or surgical decisions.[1] The panel guidelines were based on the following observations: 1) The high prevalence of vitamin D deficiency in patients with PHPT; 2) vitamin D inadequacy may worsen the clinical picture of PHPT; 3) in some patients with PHPT, vitamin D deficiency can mask hypercalcemia, and therefore obscure the diagnosis; 4) available evidence, although limited, suggests that vitamin D therapy in vitamin D-deficient patients with PHPT does not generally increase serum calcium levels. While the definition of vitamin D deficiency in the general population is still a matter of debate, the panel selected serum levels of 25-OHD <20 ng/mL as the cutoff for initiation of vitamin D therapy. This threshold was based on a study that showed circulating parathyroid hormone (PTH) levels could not be suppressed further when serum levels of 25-OHD are maintained above 20 ng/mL in healthy subjects who received vitamin D2 and calcium supplements for eight weeks.[2] Meanwhile, many physicians are reluctant to prescribe vitamin D to patients with PHPT, due to concern of worsening existing hypercalcemia and lack of sufficient data to support the safety and benefit of such intervention. Indeed, early case reports suggested that patients with PHPT and clinical evidence of vitamin D deficiency (manifested as osteomalacia) had their serum calcium levels increased from 1 to 2 mg/dL after vitamin D administration.[3,4]

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