Normal preoperative levels of parathyroid hormone signify a mild form of primary hyperparathyroidism

Authors


Abstract

Background

Primary hyperparathyroidism (pHPT) is characterized by an inappropriate serum level of parathyroid hormone (PTH) in relation to the serum level of calcium. Nowadays, patients often are diagnosed with an overtly asymptomatic pHPT with mild or even intermittent hypercalcaemia. Indeed, health screening surveys have shown that a significant proportion of patients with pHPT is normocalcaemic. Most studies also demonstrate patients with PTH levels in the upper normal range. The aim of the present study was to define subgroups of patients with mild pHPT, which potentially could give valuable insights into the pathogenesis of the disease.

Methods

Two hundred and seven consecutive patients, 157 women and 50 men, operated for pHPT were investigated with biochemical variables known to reflect PTH activity and calcium metabolism, and bone mineral content. The preoperative diagnosis of pHPT was based on the presence of hypercalcaemia combined with an inappropriate serum concentration of PTH. Thus, no patient was persistently normocalcaemic. Mean(s.d.) age of the patients was 64(14) years and mean(s.d.) serum level of calcium was 2·78(0·19) mmol l−1. On the basis of serum levels of PTH and calcium the day before surgery, patients were divided into subgroups.

Results  

One hundred and sixty-two patients (78 per cent) had raised levels of PTH and calcium the day before surgery (group 1), 25 patients (12 per cent) had a raised level of PTH and normal level of calcium (intermittent normocalcaemia) (group 2) and 20 patients (10 per cent) had a normal PTH level and raised calcium level (group 3). Between-group analyses demonstrated differences between groups in age, bone density, renal function and adenoma weight, and serum levels of alkaline phosphate, osteocalcin and urate. Except for lower adenoma weights, patients in group 2 did not essentially differ from those in group 1. However, patients in group 3 were younger, had better renal function, lower biochemical bone turnover and higher bone mineral content than patients in the other two groups.

Conclusion

These data support the existence of subgroups of mild pHPT. Patients with a serum level of PTH within the normal range were characterized by less biochemical derangement and better bone mineral content. This finding suggests that PTH rather than calcium reflects the severity of the disease. © 2000 British Journal of Surgery Society Ltd

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