Evaluation of euthyroid solitary. Autonomous nodule of the thyroid gland. Importance of scintillation scanning and thyrotropin-releasing hormone testing.
The euthyroid autonomous nodule of the thyroid may escape diagnosis if only the usual criterion of less than 50% suppression of radioactive iodine uptake, (RAIU) after administration of liothyronine sodium is employed. This was the case in four patients who had thyrotoxic response to suppressive therapy, which had been given as a result of the improper conclusion that a nodule was hyperplastic, after the RAIU had fallen. We studied 95 patients with a solitary functioning nodule and found ten euthyroid persons (11 tests) in whom scintiscans showed persistent function in the nodule in spite of suppression of the RAIU by more than 50%. A thyrotropin-releasing hormone test demonstrated lack of thyroid-stimulating hormone responsiveness after administration of liothyronine, proving adequacy of the suppressive dose. Diagnosis of an autonomous nodule should not be excluded unless a scintiscan reveals that its function, in distinction to the rest of the gland, is curtailed by adequate suppression.