Defective iodide transport and normal organification of iodide in cold nodules of the thyroid

Monoamine oxidase (MAO) activity and its forms in normal and pathological human thyroid tissues

Monoamine oxidase (MAO) activity and its forms were measured in normal human thyroid glands (39 samples from necropsy and four from perinodular tissues) and in pathological thyroid glands (13 multinodular goitres, three carcinomas, seven chronic thyroiditis, five Graves' disease and seven follicular, seven foetal and five embryonal adenomas). MAO activity in carcinomas was lower than in normal perinodular thyroid control tissue; in Graves' disease, foetal and embryonal adenomas it was significantly higher than in the normal control. The use of clorgyline (a selective MAO A inhibitor) and deprenyl (selective MAO B inhibitor) allowed estimation of the relative proportion of MAO forms. A high proportion of MAO A (more than 90%) was observed, both in normal and in pathological thyroid tissues. Changes in total thyroid MAO activity, but not in its forms, were found in different pathologies of the thyroid gland.

Management of thyroid nodules

This review describes the frequency of solitary thyroid nodules and their relationship to thyroid cancer. The importance of selecting patients appropriately for surgical excision is stressed. The factors predisposing to nodule formation and to a nodule being malignant are reviewed with emphasis that prior radiation exposure does not appear to increase the likelihood that a given nodule harbors a malignancy. In considering the laboratory evaluation of thyroid nodules, the limitations of isotope scans and ultrasonography are noted. Fine needle aspiration biopsy is described as revolutionizing the management of thyroid nodules and decreasing unnecessary operations. In the context of the natural history of differentiated thyroid cancer, the application of a decision analysis model to management options is described in some detail, and a cost-effective management regimen is recommended with fine needle aspiration biopsy as the initial procedure.

Iodide-induced thyrotoxicosis in a thyroidectomized patient with metastatic thyroid carcinoma

An unusual case of iodide-induced thyrotoxicosis is documented in this article. The patient was a 64-year-old euthyroid man with acromegaly. He also had multiple follicular and papillary thyroid carcinomas with a metastatic lesion in the lumbar vertebrae. After a total thyroidectomy, he became slightly hypothyroid, and the lumbar lesion began to incorporate 131I by scintigraphy. When an iodine-containing contrast medium happened to be injected, a transient increase of serum thyroid hormone level was observed. After complete thyroid ablation with 83 mCi of 131I, the oral administration of 100 mg of potassium iodide for 7 days induced a prominent increase of serum thyroid hormone level. These findings indicated that the metastatic thyroid carcinoma could produce excess thyroid hormone insofar as a sufficient amount of iodide was given. Although this is the first report of such a case, iodide-induced thyrotoxicosis may not be rare in patients with thyroid carcinomas because the Wolff-Chaikoff effect is thought to be lost, and the organic iodinating activity and lysosomal protease activity are well-preserved.

Iodide organification defect in a cold thyroid nodule: absence of iodide effect on cyclic AMP accumulation

A follicular adenoma of the thyroid was 'hot' one hour after 99mTc pertechnetate administration, but 'cold' 24 h after 131I iodide administration. Incubation of the tissue in vitro demonstrated a defect in iodide binding to proteins that was abolished by addition of an H2O2 generating system. In this tissue iodide failed to inhibit TSH-induced cyclic AMP accumulation. The results show that iodide oxidation is required for its inhibitory action on cyclic AMP accumulation in human thyroid.