A 64-year-old woman presents with nephrolithiasis and primary hyperparathyroidism. Her family history is unremarkable A Tc-99 sestamibi scan demonstrates a focus of activity near the left lower pole of the thyroid gland. The next step in her management should be A. left neck exploration. B. confirmatory 24-hour urinary calcium level. C. neck ultrasound. D. observation with repeat calcium and parathormone levels in 6 months. E. contrast-enhanced dynamic CT scan of the neck and chest (4-dimensional CT). https://twitter.com/DrATEFAHMED/status/1645517671960641552?s=20 ANSWER: C The diagnostic workup for primary hyperparathyroidis (pHPTH) is relatively simple biochemically. The serum calcium level will be elevated with a concomitant inappropriately elevated parathormone level (PTH). Confirmatory testing can include elevated levels of urinary calcium excretion, effectively ruling out familial hypocalciuric hypercalcemia. A normal Vitamin D level will exclude low levels as a cause of the elevated PTH level. Other associated biochemical findings can include depressed serum phosphate with a serum chloride-to-phosphate ratio of greater than 33. Once the biochemical diagnosis of pHPTH is made, further testing is unnecessary and the decision for surgery is made in concert with a surgeon familiar with endocrine surgery. Criteria for surgical intervention are well established in pHPT. In general, the symptomatic patient or the patient with evidence of organ dysfunction from hypercalcemia should have a parathyroidectomy. The decision for further imaging is based solely on the operative technique planned. If traditional 4-gland neck exploration is planned, no further imaging is necessary. In the hands of an experienced surgeon, additional imaging only increases costs without significant benefit. If a patient is a candidate for focused parathyroidectomy, or "minimally invasive" parathyroidectomy, imaging techniques to localize a solitary adenoma are appropriate. The sensitivity of Tc-99 sestamibi scan ranges from 65 to 85% and varies across institutions widely. More importantly, the relatively low specificity of any single imaging test to diagnosis a solitary adenoma, as opposed to multiple adenomas or hyperplastic disease, is not sufficient to guide focused surgical techniques. Most experienced surgeons use a 2-imaging test algorithm, and if concordant and confirmatory of solitary adenoma, focused exploration may be appropriate. It is inappropriate to offer focused parathyroidectomy based on a single positive image or discordant imaging results. The most commonly used imaging tests to guide exploration options, from least expensive to most expensive, are neck ultrasonography, Tc- 99 sestamibi scanning, and contrast-enhanced CT scan of the neck. Ultrasonographic imaging of the neck is inexpensive,reliable in experienced hands, and office based. It has the added benefit of ruling out any additional thyroid pathology in the setting of planned neck exploration