Coexistent thyroid pathology may impair parathyroid localization in primary hyperparathyroidism: usefulness of PTH assay in FNAB fluid wash-out.

Purpose: To assess the value of parathyroid hormone (PTH) assay in fine needle aspiration biopsy wash out fluid (FNA-PTH) to localize hyperfunctioning parathyroids (HP), in primary hyperparathyroidism (pHPT) associated to nodular thyroid diseases. Subjects and Methods: A total of 58 lesions suspect for HP from 40 patients with pHPT associated to multinodular goiter (MNG) and/or Hashimoto's thyroiditis (HT) were considered. Sixteen HP (form 16 patients) unequivocally localized by sestaMIBI scintigraphy (MIBI) and neck ultrasound (US) (group I), were compared to 42 suspect lesions (from 24 patients) displaying uncertain parathyroid localization (group II). In all cases US, MIBI, FNA-PTH and FNA-cytology and were performed. FNA-PTH was considered indicative for HP when it exceeded the value of 103 pg/ml (i.e. three times the maximal level found in not-HP lesions). Results: MIBI correctly identified all HP in group I patients, while a lower diagnostic accuracy (sensitivity 70 % , specificity 25 %) was observed in group II, due to the presence of both MIBI negative HP (more frequently observed in HT [6/9, 66,7%] vs MNG [6/31, 19.3%], p< 0.02) and MIBI positive thyroid nodules. In contrast, FNA-PTH correctly identified all HP (38 adenomas, 2 hyperplastic parathyroid, and 1 carcinoma) in both groups of patients, with 100% sensitivity and specificity. FNA-cytology, although 100% specific, showed low sensitivity (53.7%), with no differences between the two groups. Conclusions: In pHPT coexistent thyroid pathology (particularly HT) may cause variable degree of mismatch between MIBI and US resulting in difficult HP localization. In these cases FNA-PTH resulted an accurate and safe tool to localize HP. However, due to its reported potential risks, this procedure may be advised only to patients with uncertain HP localization.