Endocrine Abstracts

Introduction: Normocalcemic primary hyperparathyroidism (NPHPT) is defined as a condition in which persistently normal serum calcium levels are observed in the presence of high levels of parathyroid hormone (PTH). NPHPT is a new entity which possibly represents a clinically symptomatic disease and which has generated a considerable scientific interest.

Aim: To compare the clinical and laboratory data between the normocalcemic and hypercalcemic forms of PHPT.

Materials and methods: A comparative study of 357 patients with PHPT wich were separated into normocalcemic (n=56) and hypercalcemic (n=301) subgroups on the basis of their fasting serum total calcium value. Bone mineral density (BMD) and T-scores were evaluated by densitometry of the lumbar spine, femoral neck and total of the radius. Nephrolithiasis and bone fractures were documented by a review of the medical records.

Results: Patients with NPHPT had, on average, a lower serum PTH concentration 150 pg/ml±115 (N 15–65, Me 114) and a lower serum calcium level 2.44 mmol/l±0.08 (N 2.15–2.55) vs hypercalcemic PHPT – 408 pg/ml±651 (Me 186) and 2.89 mmol/l±0.3 respectively. There was no significant difference in urine calcium excretion. The frequency of nephrolithiasis was 27% in normocalcemic patients and 16% in the hypercalcemic ones (P<0.05). There were no statistical differences in relation to BMD of the lumbar spine and femoral neck, but BMD significantly differed in the total radius area. BMD in the total radius was 0.423 g/cm² (Me 0.415), mean T-score was −2.2 S.D. of the normocalcemic patients, 51.8% had osteoporosis in at least one of the three sites evaluated. In addition, normocalcemic patients differed from hypercalcemic patients by lower values of markers of bone turnover osteocalcin and β-C-telopeptide, P<0.05. 20.4% of normocalcemic patients had a previous history of fractures compared to 20.3% of hypercalcemic patients (P>0.05).

Conclusion: NPHPT is at present one of the most common reasons for consultation in bone metabolism departments, especially in postmenopausal women. Identifying these patients is important because of the consequences of untreated hyperparathyroidism, which include nephrolithiasis, osteoporosis and atraumatic fractures.