Normocalcemic hyperparathyroidism and hypoparathyroidism in two community-based nonreferral populations

Normocalcemic primary hyperparathyroidism is typically identified after referral to a specialty clinic. At diagnosis, patients demonstrate features seen in hypercalcemic primary hyperparathyroidism. Normocalcemic hypoparathyroidism has been discovered after hypocalcemia unmasked after bisphosphonate administration.

We hypothesized that screening unselected, nonreferral populations, such as The Osteoporotic Fractures in Men (MrOS) study and Dallas Heart Study (DHS), would identify asymptomatic subjects with normocalcemic hyperparathyroidism and hypoparathyroidism.

Normocalcemic hyperparathyroidism was defined as serum PTH greater than the upper reference range with normal albumin-adjusted serum calcium, excluding common secondary causes (renal failure [estimated glomerular filtration rate <60 mL/min], 25-hydroxyvitamin D <20 ng/mL, and thiazide use), and normocalcemic hypoparathyroidism as PTH below the reference range with normocalcemia. Cross-sectional data were obtained from MrOS, and longitudinal data (baseline and 8 years) from DHS.

In 2364 men from MrOS, we identified 9 with normocalcemic hyperparathyroidism (prevalence 0.4%) and 26 with normocalcemic hypoparathyroidism (1.1%). In 3450 men and women from DHS, we identified 108 with normocalcemic hyperparathyroidism (3.1%) and 68 with normocalcemic hypoparathyroidism (1.9%). Of the 108 normocalcemic hyperparathyroid subjects, 64 had follow-up data. Hypercalcemic primary hyperparathyroidism developed in 1 subject whereas 13 (0.6% of the follow-up cohort) showed persistently elevated PTH levels with normocalcemia. Of the 26 normocalcemic hypoparathyroid subjects with follow-up data, none developed overt hypoparathyroidism and 2 (0.09%) had persistent evidence of normocalcemic hypoparathyroidism.

This study documents normocalcemic primary hyperparathyroidism and hypoparathyroidism identified among community-dwelling individuals. Larger studies are needed to determine the true prevalence and natural history of these parathyroid disorders.