Unexpected results using rapid intraoperative parathyroid hormone monitoring during parathyroidectomy for primary hyperparathyroidism.

Rapid intraoperative parathyroid hormone (RIOPTH) monitoring predicts complete removal of all hypersecreting tissue by means of a significant parathyroid hormone (PTH) decrease. In this study we have tried to provide an explanation for some unexpected results of RIOPTH monitoring observed during a series of 125 conventional parathyroidectomies for primary hyperthyroidism, discussing the possible consequences on the surgical strategy. Three main groups can be recognized: (1) spikes: a PTH increase 10 minutes after removal of the diseased gland was observed in three patients; (2) false-negative results: six patients showed an inadequate PTH decreases at 10 minutes, three of them resulting in cure at 20 minutes (all six patients were cured at follow-up); (3) false-positive results: five patients with multiglandular disease showed a PTH decrease to a cure level despite excision of one adenoma only (in two of these patients a 20-minute sample showed a PTH increase soon after manipulation of the second adenoma). We concluded that the spike, almost certainly a consequence of manipulating the adenoma, when detected should be considered the "true" baseline value. False-negative results are to some extent related to undetected spikes. The assay used for RIOPTH determination and PTH half-life variability may also play a role. A false-negative result usually prolongs the surgical time. False-positive results are usually related to a double adenoma, one functionally prevailing over the other. Because in our experience manipulation of the second adenoma brought a PTH increase detected with RIOPTH monitoring, we believe that the second adenoma should be excised.