Long-Term Calcium Monitoring Post Parathyroidectomy for Primary Hyperparathyroidism.

Background:  Cure rates following parathyroidectomy for primary hyperparathyroidism are excellent, with well-documented low short-term recurrence rates of hypercalcaemia. Rates of long-term recurrence have been investigated to a lesser extent, but recent studies have reported higher than anticipated rates. This study sought to evaluate recurrence rates at more than four years post seemingly corrective surgery and depending on the findings, propose whether recommendations of annual calcium monitoring post-parathyroidectomy are appropriate based on the limited data available at the time of formulating guidelines.

Methods: Fifty-two sequential parathyroidectomies for primary hyperparathyroidism from 2014-2016 from a single unit were retrospectively followed up with serum calcium levels. A hospital computer system was used to collect data on pre-operative, immediate post-operative and most recent follow-up calcium levels. Patients were excluded if there was no minimum of 48 months between the operation date and most recent calcium. Recurrence was defined as hypercalcaemia more than six months after eucalcaemia post-parathyroidectomy.

Results: Of the 52 cases analysed, two were lost to long-term follow-up, two patients died during the follow-up period while 10 did not meet the inclusion criteria of at least 48 months follow-up. This resulted in a cohort of 38 patients (mean age 66.4 years, 78.9% female). The median follow-up of 73.17 months (range 48.77-95.47 months) demonstrated a hypercalcaemia recurrence of 5.26% (2/38 patients). These cases were due to misdiagnosed parathyroid hyperplasia as opposed to suspected adenoma. Therefore, the long-term cure rate was 94.74% (36/38 patients).

Conclusion: These findings support the high cure rates and low recurrence rates of the numerous short-term studies already performed despite a longer follow-up period. This is in contrast to recent series which have documented a higher recurrence in the long-term. This study would, therefore, suggests recommendations of annual calcium monitoring are excessive and that less frequent calcium monitoring is necessary in the first few years post-operation. However, the 5.26% recurrence rate in this study is not insignificant and follow-up is still paramount. Therefore, following the initial post-operative assessment, the authors propose a follow-up at the five-year mark and an annual continuation from this point forward due to the evidenced delayed recurrence of hypercalcaemia.