Persistent elevated serum parathyroid hormone levels with normocalcaemia after parathyroidectomy: Secondary hyperparathyroidism or pseudo- hyperparathyroidism?

INTRODUCTION

This study aimed to determine the time to normalisation of postoperative parathyroid hormone levels after successful parathyroid surgery and to analyse the pathophysiology of postoperative normocalcaemic hyperparathyroidism.

METHOD: An observational retrospective study was conducted on a cohort of 186 patients who had undergone parathyroidectomy for primary hyperparathyroidism over a 5-year period. Demographic characteristics, surgical and histopathological data, bone densitometry (pre-and postoperative pharmacological treatment), creatinine plasma levels, and pre-and postoperative parathyroid hormone, calcium and vitamin D levels were recorded as predictive variables. The time to normalisation of the postoperative parathyroid hormone levels was recorded as the output variable. A univariate analysis was performed to investigate the factors related to the time to normalisation of parathyroid hormone levels.

RESULTS

The final study sample was comprised of 176 patients, 46 of which (26.1%) had elevated postoperative parathyroid hormone levels and normocalcaemia. The median time to normalisation of the postoperative parathyroid hormone levels was 6 months. The cumulative probability of having normal parathyroid hormone levels 30 months after surgery was 89%. The time to normalisation was associated only with preoperative parathyroid hormone levels (P = .007; HR: 0.998). Vitamin D and creatinine levels were not associated with time to normalisation of parathyroid hormone levels (P = .744).

CONCLUSIONS

Persistently elevated postoperative parathyroid hormone levels with normocalcaemia may occur in one-quarter of patients after parathyroidectomy. Parathyroid hormone levels normalise in up to 90% of cases by 30 months. A high preoperative parathyroid hormone level is predictive of postoperative normocalcaemic hyperparathyroidism, and vitamin D deficiency does not seem to influence the pathogenic mechanism.