Impaired iodide organification in autonomous thyroid nodules.

Context: The clinical evolution of autonomous thyroid nodules (ATN) is unpredictable, and thyrotoxicosis is observed at variable nodule size. In vitro data suggest that hydrogen peroxide production is decreased in ATN, indicating intranodular iodide organification impairment.

Objective: We aimed to determine iodide organification efficiency in ATN and its relationship with thyroid status in patients.

Design: Forty-six patients with a single ATN on the 123I thyroid scan were included in the study. Biological evaluation and iodine perchlorate (I-ClO4) discharge test were carried out in all subjects.

Setting: The study took place at an academic hospital.

Results: Among the 46 patients, 28 patients (61%) had a positive I-ClO4 discharge test with a mean +/- sd value of discharge of 42 +/- 13%, and 18 (39%) had a negative discharge test with mean +/- sd of 5 +/- 9%. In the group of patients with a negative discharge test but not in the group with a positive test, serum-free T3 and free T4 concentrations were significantly correlated with the 123I uptake. The severity of hyperthyroidism was not different between both groups.

Conclusions: Intranodular iodide organification was impaired in most patients with ATN. Whether differences in organification capability could predict the risk for evolution to overt hyperthyroidism in patients with ATN remains to be established.