The impact of obesity on the presentation of primary hyperparathyroidism

Context: Obesity has been associated with elevated serum PTH (sPTH) in the general population. Obesity may also alter the clinical presentation in patients with primary hyperparathyroidism (PHPT). Objectives: The objectives of the study were to compare the clinical presentation of obese (OB) vs nonobese (NO) PHPT patients and to assess the impact of obesity on the presentation of PHPT independent of serum calcium and PTH. Patients: Consecutive PHPT patients who underwent parathyroidectomy between 2003 and 2012 by a single surgical group participated in the study. Setting: The study was conducted at an academic medical center. Design: Cross-sectional review of records of preoperative demographic, historical, laboratory, and densitometry findings and intraoperative pathological findings were compared in OB vs NO patients. Main Outcome Measures: The prevalence of nephrolithiasis and osteoporosis was measured. Results: Two hundred forty-seven PHPT patients were included in this analysis. Fifty percent were OB and 79% were women. Mean body mass index was 25.3 ± 3.3 and 36.0 ± 5.2 kg/m² in the NO and OB groups, respectively. Age, gender, and race distribution was similar between the two groups. Serum calcium was similar between the groups (11.0 ± 0.7 mg/dL in NOvs 11.1 ± 0.9 mg/dL in OB, P = .13), whereas sPTH was higher in OB (151 ± 70 vs 136 ± 69 pg/mL, P = .03). The OB group exhibited higher prevalence of hypercalciuria (urine calcium > 400 mg per 24 h) (41% vs 23% in NO, P = .01) and nephrolithiasis (36% vs 21% in NO, P = .03). Despite higher sPTH, OB patients showed higher bone mineral density and a lower rate of osteoporosis (21% vs 35%, P = .05). Differences in the prevalence of hypercalciuria and osteoporosis between the groups persisted after adjustment for age, race, estimated glomerular filtration rate, gender, sPTH, and calcium. Conclusions: In PHPT patients, obesity is a risk factor for hypercalciuria and nephrolithiasis and is protective against osteoporosis. The impact of parathyroidectomy on the clinical features of obese PHPT patients merits further evaluation.