When to order a sestamibi (technetium-99m-sestamibi) scan for primary hyperparathyroidism (PHPT)?

When to Order Sestamibi Scan for Primary Hyperparathyroidism (PHPT)

Sestamibi scans should be ordered as part of the initial imaging approach for patients with biochemically confirmed primary hyperparathyroidism who are surgical candidates, ideally combined with neck ultrasound to maximize accuracy in parathyroid localization. 1

Initial Diagnostic Approach

• First confirm PHPT biochemically with:
  • Elevated or inappropriately normal PTH with hypercalcemia
  • Low or low-normal phosphorus levels
  • 25-OH vitamin D level (to rule out vitamin D deficiency)
  • Renal function tests
  • 24-hour urinary calcium

Specific Indications for Sestamibi Scanning

First-line Imaging

• Sestamibi scan with SPECT/CT combined with neck ultrasound is recommended as the best initial imaging approach for confirmed PHPT 1
• This combination maximizes accuracy and confidence in parathyroid localization for surgical planning

Specific Clinical Scenarios

• Pre-operative localization: To facilitate minimally invasive parathyroidectomy (MIP) rather than bilateral neck exploration 1
• Suspected ectopic parathyroid glands: Sestamibi with SPECT/CT has superior sensitivity (88-93%) for detecting ectopic glands 1
• Reoperative cases: Essential for patients with recurrent or persistent hyperparathyroidism after previous surgery 2
• Negative ultrasound results: Particularly useful when ultrasound is negative but clinical suspicion remains high, as these often represent posteriorly located upper gland adenomas (PLUGs) 3

Limitations and Considerations

When Sestamibi May Be Less Reliable

• Multigland disease: Lower sensitivity in cases of multigland disease (31% for multiglandular disease vs. 82% for single adenomas) 4
• Small adenomas: Less reliable for very small parathyroid adenomas
• Concomitant thyroid disease: May cause false positives or negatives

Important Caveats

• A negative sestamibi scan does not rule out PHPT - 67% of patients with negative scans still have single adenomas 5
• Without intraoperative PTH monitoring, sestamibi-directed surgery alone could lead to a higher failure rate (up to 10%) 6
• For patients with negative sestamibi scans, additional imaging modalities should be considered:
  • Thallium subtraction scans (sensitivity ~30%)
  • Ultrasound (sensitivity ~27%)
  • 4D-CT (sensitivity 62-88%)
  • MRI (sensitivity 63-93%) 1, 5

Optimal Imaging Protocol

• Dual-phase technique with SPECT/CT is preferred over planar imaging alone 4
• Images typically acquired at 20 minutes and 2 hours post-injection 4
• SPECT/CT provides both functional and anatomical information, improving localization accuracy 1

Algorithm for Imaging in PHPT

1. Biochemical confirmation of PHPT
2. Initial imaging: Sestamibi scan with SPECT/CT + neck ultrasound
3. If both positive and concordant: Proceed with minimally invasive parathyroidectomy
4. If discordant or negative: Consider additional imaging (4D-CT or MRI)
5. If all imaging negative: Bilateral neck exploration with intraoperative PTH monitoring

Remember that even with negative imaging, most patients will still have surgically correctable disease, and intraoperative PTH monitoring significantly improves surgical outcomes regardless of preoperative imaging results 6.