The biochemical cure of hyperparathyroidism (HPPT) after surgical treatment is confirmed when parathyroid hormone (PTH) and albumin-adjusted calcium (AAC) levels remain normal for at least six months after surgery. Hypercalcaemia with elevated PTH in this time period indicates persistent HPPT, and hypercalcaemia observed beyond six months after a period of normocalcaemia is considered to be recurrent HPPT. An intermediate situation between the cure and persistence of HPPT results from elevated PTH with normocalcaemia following the curative surgical resection of a primary HPPT (PPNCHPPT or post-parathyroidectomy normocalcaemic hyperparathyroidism). On average, this disorder has a prevalence of 30% outside of our setting.1, 2, 3

PPNCHPPT represents a complex clinical situation whose pathological significance has not been sufficiently defined and for which there is no consensus on follow-up and treatment.1, 2, 4, 5 At this moment in time there is no evidence that PPNCHPPT is a consequence of surgical failure.1, 2 In 30%–60% of these patients, PTH levels will normalise within 12–18 months of the procedure, and in the remainder this may mean an autonomisation of PTH secretion that should be monitored to assess for the recurrence of HPPT.1, 2, 6−9

Some predictive markers of PPNCHPPT have been described, although not unanimously,1, 2, 8, 10, 11, 12, 13, 14, 15 and a number of potentially responsible causes such as vitamin D deficiency, bone remineralisation syndrome, inadequate calcium intake or absorption, chronic kidney disease and hypercalciuria have been hypothesised. A further two aetiopathogenic mechanisms have also been proposed: an increase in the PTH secretion regulation point prompted by changes in the calcium-sensing receptors in the remaining parathyroid glands and a reduction in peripheral sensitivity to PTH.1, 2, 4, 7, 8, 9, 10, 11, 12, 13, 16, 17, 18, 19, 20, 21

The objective of this study is to determine, in our setting, the prevalence of PPNCHPPT in the first six months after a successful parathyroidectomy for a single adenoma, to evaluate the possible aetiological factors and associated predictive markers, the treatment given and outcome after more than 12 months of follow-up.