Trial Information

Use of Hypocalcemic Intraarterial Infusion Into the Thyroid/Parathyroid Bed to Localize Occult Parathyroid Adenomas

Although noninvasive diagnostic studies [ultrasound (US), computed tomography (CT),
sestamibi scanning, magnetic resonance imaging (MRI)] detect parathyroid pathology in
one-half the patients referred to NIH with recurrent or persistent hyperparathyroidism (1),
the invasive studies (direct aspiration for PTH, arteriography, venous sampling) must be
performed in the remaining patients to provide definitive preoperative localization (2).
Arteriography is positive in less than half the patients who must then proceed to
parathyroid venous sampling, a technique requiring broad experience and yielding positive,
but imprecise results as regards localization. The abrupt lowering of calcium in blood
perfusing a parathyroid adenoma should stimulate the release of PTH which could be detected
by simultaneous venous sampling. This principle, the intraarterial injection of a
secretagogue with subsequent sampling for released hormone, has been applied successfully in
the localization of insulinomas (3) and gastrinomas (4). In fact, portal venous sampling is
no longer performed in this group of patients, having been completely replaced by the
intraarterial injection of secretin or calcium as appropriate secretagogues for gastrin and
insulin.

Since release of PTH from parathyroid adenomas is stimulated by hypocalcemic perfusions, we
propose to perform serial venous sampling from a catheter positioned in the SVC to detect
abrupt elevations of PTH following the injection of contrast agent into each of the vessels
selectively catheterized at the time of parathyroid arteriography (superior thyroid
arteries, thyrocervical trunks, internal mammary arteries). Samples from the SVC catheter
will be obtained at 20 second intervals up to one minute and in some patients simultaneous
peripheral samples. An elevation of parathyroid hormone 1.5 times above the baseline will
be considered diagnostic. This technique will be applied routinely at each injection of
standard parathyroid arteriography even in the absence of an angiographically-visualized
adenoma: an elevation of PTH will provide localizing information comparable to venous
sampling. In addition, when any of the imaging studies suggest that a particular anatomic
site is the likely location of the patient's adenoma, sodium citrate, a calcium chelating
agent, will be injected into the artery supplying this region. Blood samples will be
obtained in similar fashion to those samples taken with contrast injections to measure PTH
release following sodium citrate injection and determine whether this is a more effective
hypocalcemic stimulant.