Thyroid diseases cause mismatch between MIBI scan and neck ultrasound in the diagnosis of hyperfunctioning parathyroids: usefulness of FNA-PTH assay.

DESIGN: To evaluate the efficacy of the main tools in the diagnostic localization of hyperfunctioning parathyroids (HP) in primary hyperparathyroidism (pHPT) with concomitant thyroid diseases. METHODS: Forty-three patients with pHPT associated with nodular goiter (NG, n=32) and/or autoimmune thyroid diseases (AITDs, n=11) for a total of 63 neck lesions were considered. Sixteen patients displaying HP (16 lesions), unequivocally localized by sestaMIBI scintigraphy (MIBI) and neck ultrasound (US) (group I), were compared with 27 patients (47 neck lesions) displaying equivocal parathyroid localization (group II). In all cases, neck US, MIBI scan, cytology, and parathyroid hormone assay in fine-needle aspiration washout fluid (FNA-PTH) were performed. All patients finally underwent surgery. RESULTS: According to histological examination, high FNA-PTH values (>103 pg/ml) correctly identified all HP in both groups of patients (100% of sensitivity and specificity). Both MIBI and US correctly identified all HP only in group I patients; in contrast, four patterns of mismatch between these techniques were observed in group II patients, leading to low diagnostic performances of neck US (71.4% sensitivity and 78.9% specificity) and of MIBI scan (35.7% sensitivity and 42.1% specificity). The latter was due to both false-negative (mainly in AITD) and false-positive (mainly in NG) scan images. CONCLUSIONS: Coexistent thyroid diseases are responsible for mismatch between MIBI and US images resulting in equivocal HP localization. In these cases, FNA-PTH resulted in the most accurate tool to identify HP. However, although safe, it should be advised only to patients with uncertain HP localization.

ß-thalassemia and thyroid failure: is there a role for thyroid autoimmunity?

Autoimmunity is not believed to be involved in tissue damage of Β-Thalassemia (Β-Thal), although nonspecific triggering of autoimmunity by iron overload has been suggested. We recently re-evaluated thyroid function and autoimmunity in 132 Β-Thal patients born and living in Sardinia Island, where a high prevalence of both Β-Thal and autoimmune disease is well documented and in 1002 age and sex-matched euthyroid individuals from the general population. The prevalence of primary hypothyroidism in Β-Thal patients was 28.7% (38/132), without significant difference between males (M) and females (F). Hypothyroidism was associated with smaller and hypoechoic glands, while no difference in the prevalence of anti-thyroid antibodies (ATA) was found between Β-Thal patients with or without thyroid failure. Interestingly, the prevalence of ATA in Β-Thal women (9.2%) was significantly lower than that found in age-matched euthyroid women (20.0%). Our study confirms that thyroid autoimmunity has no role in the pathogenesis of hypothyroidism in b-Thal. Moreover, the lower ATA prevalence in Β-Thal women suggests that iron overload may inhibit rather then trigger thyroid autoimmunity.