Clinical predictors of ectopic parathyroid adenomas: experience with 421 confirmed parathyroid adenoma localizations.

Purpose: This study was designed to evaluate whether patients with ectopic parathyroid adenoma (EPA) have clinical predictors by comparing them with other patients operated on for primary hyperparathyroidism (PHPT) with uniglandular parathyroid adenomas in other localizations.

Methods: The data of PHPT patients who underwent parathyroidectomy in our institution were assessed retrospectively. Abnormal gland localization was confirmed by operative and pathology reports as well as normocalcemia that lasted for at least 6 months postoperatively. The relationships of biochemical and clinical findings of patients with confirmed adenoma localizations were analyzed. In order to determine independent factors that can predict EPAs, binary logistic regression was used.

Results: Among 421 patients (83.4% female, mean age 49 ± 13.2 years) enrolled in the study, the most common adenoma localization was the lower left parathyroid gland (36.1%; p < 0.001). Parathyroid adenomas were more common in lower localizations compared to upper localizations and were smaller in size (p < 0.001 and p = 0.004, respectively). In univariate analysis, serum intact parathyroid hormone and calcium levels were found to be higher (p = 0.004 and p = 0.002, respectively), moderate/severe hypercalcemia was more common (p = 0.024), phosphorus levels were lower (p = 0.04), and postoperative transient hypocalcemia was more common (p = 0.013) in cases of EPAs than other localizations. There was no significant difference in adenoma size between EPAs and other classical localizations. In multivariate analysis, only a high serum calcium level was an independent predictor of EPAs (OR 2.017, 95% CI 1.142-3.564, p = 0.016). Receiver-operating characteristic curve analysis yielded an optimal cutoff value of 12.25 mg/dL for serum calcium (88% sensitivity, 63% specificity, and area under the curve: 0.861).

Conclusion: EPAs can cause a more biochemically distinct PHPT picture compared to parathyroid adenomas in classical localizations. A high calcium level at diagnosis may be a clinical predictor for EPAs and may affect the clinical approach and imaging technique choices. Due to the increased risk of transient hypocalcemia in patients with EPAs, caution should be exercised in postoperative follow-up. Furthermore, in the event of negative preoperative imaging, starting the parathyroid exploration from the lower left region may be a good option for the surgeon.