Clinical, Biochemical, and Radiological Profile of Normocalcemic Primary Hyperparathyroidism

CONTEXT: The clinical and radiological aspects of normocalcemic hyperparathyroidism (NHPT) are confounded by the differing methods used to rule out secondary hyperparathyroidism and by the small sample size. OBJECTIVE: To assess the clinical, biochemical, and radiological profile of NHPT compared with primary hyperparathyroidism (PHPT) and control subjects. DESIGN: Multicentric cross-sectional study. SETTING: Outpatient clinic. PATIENTS: 47 NHPT, 41 PHPT, and 39 age- and sex-matched control subjects. MAIN OUTCOME MEASURES: Calcium metabolism and bone turnover markers (BTMs). Lumbar spine, total hip, femoral neck, one-third distal radius bone mineral density (BMD). Morphometric vertebral fracture (VF) assessed by dual-energy X-ray absorptiometry. RESULTS: NHPT patients had significantly higher parathyroid hormone, 25(OH)-vitamin D levels and lower calcium × phosphorus product than controls (P < .001). Compared with PHPT, the NHPT group had significantly higher 25(OH) vitamin D levels (P = .016). NHPT had BTM levels similar to controls and PHPT. NHPT, PHPT, and controls have similar lumbar spine and femoral neck BMD. NHPT and controls had a similar radial BMD, while patients with PHPT had a lower radial BMD than both patients with NHPT (P = .031) and controls (P < .05). Using the control group as the reference, after adjustment for interacting factors, there was no increase in risk of moderate-severe VF in NHPT (odds ratio [OR] 1.04, 95% confidence interval [CI] 0.25-4.55), while PHPT had an increased risk (OR 3.81,95% CI 1.15-15.12). Seventy-nine percent of NHPT and 59% of PHPT patients fulfilled the criteria for asymptomatic hyperparathyroidism. CONCLUSIONS: The biochemical phenotype of NHPT is intermediate between PHPT and controls. In contrast, the bone phenotype resembles controls with normal bone turnover, no significant BMD impairment, and no increased risk of VF.