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PTH is parathyroid hormone. It is a regulator of bone turnover and metabolism. Too much and calcium is too high, such as in Primary Hyperparathyroidism. Too little and calcium is too low, such as in Post-operative Surgical Hypoparathyroidism (PoSH). Put more simply, we can damage the blood supply or inadvertently remove these tiny glands during thyroid surgery or bilateral parathyroid surgery.
So what is the use of this technique?
In surgery for overactive (hyperparathyroid) glands, we are looking for which of the 4 parathyroids are abnormal and over-secreting. An experienced parathyroid surgeon can find the 4 glands and recognise the abnormal one or ones in most cases. They are not always easy to find though, and with modern pre-operative localisation we often start surgery thinking we know where to look. We may find an abnormal gland as warned by the imaging, but in a small number of cases (about 1 in 20) the imaging is not complete or we don't find what we expected.
IOPTH allows us to know that the glands we have found are abnormal and once removed, that the PTH has returned to normal and the operation we have done should be successful. Research we presented in 2009 showed we could increase success in localised disease from 95% to 99+%. It can help us miss double adenomas or prevent us mistaking multi-gland disease for adenomatous disease as even in multi-gland disease each parathyroid can be a different size.
In thyroid surgery, IOPTH can help us predict damage to the parathyroids. If at the end of a total thyroidectomy the PTH levels have fallen significantly, we can examine the parathyroids. We can even use IOPTH to confirm that what we think is a parathyroid is a parathyroid and remove the most damaged one to re-implant it in a nearby muscle where it will often regain it's function and secrete PTH long term to reduce the incidence of permanent PoSH. It is a useful adjunct to try and reduce permanent rather than temporary PoSH.
