Normocalcemic hyperparathyroidism is associated with complications similar to those of hypercalcemic hyperparathyroidism.

Normocalcemic primary hyperparathyroidism (NC-PHPT) is a variant of hyperparathyroidism, characterized by normal serum calcium levels, high parathyroid hormone (PTH) and normal 25-OH vitamin D status. The present study aimed to compare complications related to hyperparathyroidism in patients with NC-PHPT and hypercalcemic PHPT (HC-PHPT). We retrospectively evaluated the records of 307 PHPT patients between January 2010 and March 2013. We excluded patients with impaired renal function and liver failure. All patients underwent a biochemical and hormonal examination including serum glucose, albumin, total calcium, phosphorus, creatinine, lipoproteins, PTH and 25-OH vitamin D. Nephrolithiasis and bone mineral density were documented based on a review of the medical records. The study population consisted of 36 (12 %) males and 271 (88 %) females with a mean age of 53.3 ± 9.5 years (29-70 years). Twenty-three of the patients were diagnosed with NC-PHPT (group 1) and 284 were diagnosed with HC-PHPT (group 2). There were no significant differences in terms of age, gender, prevalence of hypertension, low bone mineral density and kidney stones between the groups. The mean thyroid-stimulating hormone (TSH) and low-density lipoprotein (LDL) levels were significantly higher in group 1 than in group 2. Our study found that patients with NC-PHPT have similar several complications as patients with HC-PHPT. NC-PHPT patients have higher TSH levels despite being within the normal range, and higher LDL-C levels than patients with HC-PHPT. However, this relationship needs to be clarified in future studies with larger cohorts.