Fig. 15.1
Patterns of IOPTH decrease
There is no universal agreement on what constitutes an adequate decrease in IOPTH to assure cure. George Irvin and his associates rely on a 50 % decrease at 10 min from either the baseline or “at excision” IOPTH. Many surgeons feel uncomfortable terminating the procedure before the IOPTH has decreased more than 50 % from the baseline and into the normal range. Other permutations of this, all based on a percentage decrease at a set time interval, have been proposed. In most patients, IOPTH either falls dramatically after removal of the hyperfunctioning gland or falls hardly at all, making the decision to proceed with further exploration relatively simple. It should also be noted that in some patients the baseline IOPTH is actually in the normal range. Even in these patients substantial decreases in IOPTH are usually observed following removal of the hyperfunctioning parathyroid(s).
Early in my experience, it became apparent that patients whose decrease in IOPTH level barely met the standard criteria had a higher incidence of persistent hyperparathyroidism postoperatively compared with those in whom the IOPTH decrease was dramatic. Requiring a greater decrease in IOPTH may result in fewer cases of persistent hyperparathyroidism after surgery but results in an increase in the number of unnecessary bilateral explorations. In a retrospective analysis of 194 patients, we found that persistent hyperparathyroidism after surgery almost always occurred in those patients whose final IOPTH was >40 pg/ml (although in all patients IOPTH decreased by at least 50 % and into the normal range) regardless of the percentage decrease from baseline. It would appear that the absolute final value of IOPTH is more predictive of success than the percentage decrease.
Some authors have suggested that MIP can be performed with a high success rate in many patients without the time and expense of IOPTH measurement. They argue that in a patient who only has a solitary adenoma that is localized by appropriate imaging, measurement of IOPTH is unnecessary. Kebebew et al. proposed a simple scoring system based on the results of preoperative sestamibi scans, ultrasonography, serum calcium level, and PTH that was 99 % accurate in predicting the presence of a single hyperfunctioning parathyroid. Others have suggested that the presence of concordant sestamibi and ultrasonography studies reliably predicts single-gland hyperparathyroidism and that measurement of IOPTH is not necessary in these patients. Our own experience differs from this. In patients with concordant sestamibi and ultrasonographic images demonstrating a solitary adenoma, 8 % of patients had additional enlarged hypercellular parathyroid glands found during further exploration performed because the decrease in IOPTH did not meet our criteria for successful surgery.
Other authors have criticized the entire concept of MIP based on IOPTH or radio guidance (see Chap. 5). Siperstein and his colleagues at the Cleveland Clinic have reported the results of their practice of measuring IOPTH while performing bilateral parathyroid exploration on all patients. In patients with preoperative imaging identifying a single adenoma and in whom IOPTH met the usual criteria for successful surgery following removal of the imaged parathyroid, 16 % were found to have additional enlarged hyperfunctioning parathyroid glands on bilateral exploration. This observation is difficult to reconcile with the results of many large series of focused, single-gland explorations in which the failure rate is only about 2 %. It would appear that either many patients will recur over time or that the enlarged, hypercellular parathyroid glands identified by Siperstein and his colleagues are of no clinical (and functional) significance.
There is another possible explanation for this observation. It has been well established that at least 15 % of patients whose calcium returns to normal after apparently successful parathyroidectomy have persistently elevated PTH postoperatively. In many patients, this is due to vitamin D deficiency or mild secondary hyperparathyroidism due to hypocalcemia. In some, however, the persistently elevated PTH is associated with normal vitamin D levels and calcium in the high normal range. These patients may indeed have mild persistent primary HPT and have been demonstrated to have a relatively high incidence of recurrent HPT with hypercalcemia. It is possible that those patients with additional enlarged, hypercellular parathyroid glands identified by Siperstein (which would not have been removed if exploration was terminated after an adequate decrease in IOPTH) may be responsible for this phenomenon.
Norman, in Tampa, was an early and enthusiastic advocate of MIP. Rather than assess the adequacy of parathyroidectomy by IOPTH, he used radio guidance to demonstrate that all hyperfunctioning parathyroid tissue had been removed. In a recent publication, he reported that long-term follow-up of his patients who had undergone limited exploration revealed a 6 % failure rate compared to a 99.4 % cure rate in those who had bilateral exploration. He concludes from this observation that limited exploration has an unacceptable high failure rate and should be abandoned. An alternative interpretation of his data, however, is that radio guidance is not an adequate substitute for IOPTH and that the difference in long-term outcome observed comparing limited with bilateral exploration would not have occurred had he determined the adequacy of surgery by IOPTH.
It will require many years of careful follow-up to confirm that MIP results in long-term cure rates of hyperparathyroidism comparable to bilateral exploration. Most studies published to date certainly support this. It is not adequate to follow serum calcium alone. At least 13 % of patients undergoing surgery for HPT are normocalcemic. In recent years in our practice, that figure has reached 19 %. These patients have significant clinical disease. Return of postoperative calcium levels to the normal range without knowledge of PTH levels is not a guarantee that the patient does not have mild persistent hyperparathyroidism. Serum calcium and PTH should be followed postoperatively, and in those patients with persistently elevated PTH, bone densitometry should be performed periodically. Lack of improvement or increase of bone loss would suggest that persistently elevated PTH, even in the presence of normocalcemia, is clinically significant. At the present time, there is insufficient data to suggest that MIP should be abandoned.
Other Uses of IOPTH
The measurement of IOPTH can help the surgeon in clinical situations other than MIP. There are many patients in whom bilateral exploration is necessary. Patients with inconclusive preoperative imaging or patients in whom imaging suggests multiple hyperfunctioning parathyroid glands are not candidates for MIP. Even the most experienced parathyroid surgeons can have difficulty differentiating normal from minimally enlarged, hyperfunctioning parathyroid glands, and persistent hyperparathyroidism can occur after bilateral exploration. Multiglandular parathyroid hyperplasia is not necessarily symmetrical. The presence of one obviously enlarged parathyroid does not mean that some of the smaller, relatively normal appearing glands are not hyperfunctioning. Frozen section biopsy of minimally enlarged parathyroid glands jeopardizes their viability. In addition, pathologists may not be able to differentiate normal from hypercellular parathyroid glands on frozen section when given a very small biopsy sample. When performing a bilateral exploration, persistence of IOPTH elevation following removal of an obviously enlarged parathyroid should prompt the removal or biopsy of additional parathyroid glands that appear relatively normal.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
