In an 84‑year‑old woman with borderline hypercalcemia, markedly elevated intact parathyroid hormone, and mild renal impairment, is thyroid scintigraphy indicated?

Thyroid Scintigraphy is NOT Indicated

In this 84-year-old woman with borderline hypercalcemia, markedly elevated intact PTH, and mild renal impairment, thyroid scintigraphy is not indicated—this is primary hyperparathyroidism requiring parathyroid-specific imaging, not thyroid imaging.

Why Thyroid Scintigraphy is Wrong Here

The clinical picture clearly points to primary hyperparathyroidism (PHPT): elevated PTH with hypercalcemia. The key principle is that imaging has no utility in confirming or excluding the diagnosis of PHPT—the diagnosis is biochemical 1. More importantly, you need parathyroid localization imaging, not thyroid imaging.

The Correct Imaging Approach

For PHPT localization, the appropriate studies are 1:

• 99mTc-sestamibi parathyroid scintigraphy (not pertechnetate thyroid scan)
• 4-D parathyroid CT (multiphase CT with contrast)
• Ultrasound of the neck for parathyroid adenoma localization

These modalities target parathyroid tissue specifically. The goal is to localize a parathyroid adenoma to facilitate minimally invasive parathyroidectomy, which offers shorter operating times, faster recovery, and decreased costs compared to bilateral neck exploration 1.

When Thyroid Scintigraphy Might Confuse Matters

99mTc-pertechnetate thyroid scintigraphy evaluates thyroid function and identifies hot/cold thyroid nodules—this is irrelevant to parathyroid disease. The only scenario where thyroid imaging becomes relevant is the rare case where hyperthyroidism coincidentally presents with hypercalcemia 2, but this patient has markedly elevated PTH, which excludes thyroid-mediated hypercalcemia.

Critical Pitfall to Avoid

Do not order thyroid scintigraphy when you suspect parathyroid disease. While both parathyroid and thyroid imaging use nuclear medicine techniques, they serve completely different purposes:

• Parathyroid imaging (sestamibi): Localizes hyperfunctioning parathyroid tissue
• Thyroid imaging (pertechnetate): Assesses thyroid nodule function

The case report 2 illustrates how a toxic thyroid adenoma can mimic parathyroid disease on sestamibi scanning, but that patient had only "mildly elevated" PTH—not the marked elevation described in your patient.

The Appropriate Workup Algorithm

1. Confirm PHPT biochemically (already done: elevated PTH + hypercalcemia)
2. Assess for complications: bone density scan, renal function (already showing mild impairment), vitamin D level 3
3. Order parathyroid localization imaging: Start with either sestamibi scan or ultrasound based on local expertise 1
4. Consider 4-D parathyroid CT if initial imaging is nonlocalizing or discordant 1
5. Refer to endocrine surgery for minimally invasive parathyroidectomy

Special Consideration for This Patient

The mild renal impairment raises the question of secondary hyperparathyroidism, but the hypercalcemia excludes this—secondary hyperparathyroidism causes hypocalcemia, not hypercalcemia 1. At 84 years old with borderline hypercalcemia, consider whether surgery is appropriate based on symptoms, complications, and surgical risk, but imaging choice remains the same if surgery is planned.