Endocrine Abstracts

Introduction

Primary hyperparathyroidism (PHPT) is a common endocrine disorder and classically associated with hypercalcemia (HHPT). There is a newest variant of PHPT, defined by normal albumin-corrected calcium levels - normocalcemic PHPT (NHPT) – which may represent an early stage of HHPT. Nevertheless, there is limited data on how this variant presents clinically and biochemically.

Aim

To evaluate the demographic, biochemical and clinical profile of NHPT, comparing with HHPT.

Methods

Retrospective single center study that included subjects with a confirmed diagnosis of PHPT followed at our hospital from November 2019 to November 2020. We excluded patients with malignancies and under treatment with glucocorticoids, cinacalcet, bisphosphonates and denosumab. Patients were categorized in two groups – HHPT and NHPT – whether they had hypercalcemia or not, respectively. Nephrolithiasis was documented by kidney ultrasound. Bone mineral density (BMD) at lumbar spine, femoral neck and one-third distal radius was documented by Dual-energy X-ray absorptiometry (DXA).

Results

We included 30 patients with HHPT and 28 with NHPT. The mean age was 59 ± 15 and 61 ± 15 years in NHPT and HHPT, respectively. There were predominantly females (80% NHPT and 78.6% HHPT). The group of NHPT presented with lower levels of PTH (122 pg/ml [101–142] vs 309 pg/ml [216–389], P < 0.001), albumin-corrected serum calcium (9.7 mg/dl [9.1–10.0] vs 11.4 mg/dl [11.1–12.2], P < 0.001), and higher phosphate concentration (3.6 mg/dl [2.7–4.3] vs 2.8 mg/dl [2.3–4.1], P = 0.028). There were no differences between groups in nephrolithiasis (40% NHPT vs 53.6% HHPT, P = 0.300), in femoral neck T score (–1.05 [–2.25; –0.63] vs –1.35 [–2.10; –1.20], P = 0.159) and lumbar spine T score (–1.45 [–2.70; –0.58] vs –2.35 [–3.20; –1.28], P = 0.093). Patients in the NHPT group showed a higher one-third distal radius T score compared to HHPT (–1.05 [–2.93; –0.08] vs –2.50 [–2.75; –1.70], P = 0.028). The prevalence of osteoporosis was 25% in NHPT and 41.7% in HHPT (P = 0.246). The prevalence of osteopenia at femoral neck and distal radius was lower in the NHPT group (40% vs 70.8%, P = 0.040).

Conclusion

Considering biochemical and clinical features, NHPT appears to represent an early stage of HHPT. However, it presents with high rates of nephrolithiasis and osteoporosis, reinforcing the need to recognize and treat this entity according to defined criteria. BMD at distal radius was more preserved in NHPT, corroborating the association with cortical, but not trabecular, bone loss. Therefore, one-third distal radius BMD should be assessed in all patients with PHTP.