75Se selenomethionine as a scanning agent for the differential diagnosis of the cold thyroid nodule

Abstract

A localized area of thyroid tissue which fails to concentrate radioiodine or 99m Tc pertechnetate (a thyroid nodule) is highly suspicious for the presence of thyroid carcinoma. Cystic disease of the thyroid may produce an identical scan. A neoplastic thyroid nodule utilizes amino acid for protein synthesis, while a cystic nodule concentrates neither halogen nor amino acids. The conversion from a halogen cold to a selenomethionine hot nodule usually indicates the presence of a solid lesion in the area of interest. Nodules that remain are usually caused by benign cystic disease of the thyroid. False negative studies occurred in five cases in our series of 21 patients with malignant neoplasms of the neck (24%). Seventy-six per cent of patients with neck neoplasms had positive scans. A benign adenoma of the thyroid cannot be differentiated from a carcinoma, however selenomethionine may help answer the question of whether a clinically palpated lesion is solid or cystic. In view of the high rate of false negatives in this small series, this test must be used with caution in guiding clinical therapy.