Thyroid nodule, toxic

An autonomous thyroid nodule (toxic adenoma) is a discrete thyroid mass whose function is independent of pituitary control. Hyperthyroidism usually occurs with larger nodules (i.e., those greater than 3 cm in diameter). 

Thyroid autonomy appears as a solitary toxic nodule or toxic multinodular goitre. In toxic thyroid, the nodule s synthesis and secretion of thyroid hormones is autonomous from the thyroid-stimulating hormone (TSH), which is produced in the pituitary gland. Accordingly TSH is suppressed and the extranodular thyroid tissue is functionally downregulated. Thyroid autonomy occurs frequently in iodine-deficient countries, whereas it is much less common in iodine-sufficient areas. Constitu-tively activating mutations in the TSH receptor and in the Gs a protein are the major molecular aetiology of toxic thyroid nodules. 

The common causes of thyrotoxicosis are shown in Table 41-6.29,30 Thyrotoxicosis can be related to the presence or absence of excess hormone production (hyperthyroidism). Graves disease is the most common cause of hyperthyroidism. Thyrotoxicosis in the elderly is more likely due to toxic thyroid nodules or multinodular goiter than to Graves disease. Excessive intake of thyroid hormone may be due to overtreatment with prescribed therapy. Surreptitious use of thyroid hormones also may occur, especially in health professionals or as a self-remedy for obesity. Thyroid hormones can be obtained easily without a prescription from health food stores or Internet sources. 

From a functional point of view, euthyroid diffuse goiter and hypofunctional thyroid nodules have to be discerned from hyperthyroid conditions, mainly toxic adenoma and toxic multinodular goiter. 

Thyroid Autonomy Activating mutations of the TSH receptor are the most common known molecular etiology of thyroid autonomy. They were found in up to 70% of toxic thyroid nodules (Krohn et al, 2005). 

TOXIC NODULAR GOITER. Growth of thyroid nodules sometimes occurs without TSH simulation. In some cases, there may be escape of thyroid hormone production from the control of the pituitary then, the uncontrolled nodules are described as having become autonomous. This condition is more likely to be found in older persons who may have cardiovascular disorders as a consequence, but have none of the other characteristics of hyperthyroidism. 

Toxic adenomas may result in hyperthyroidism with larger nodules. Because there may be isolated elevation of serum T3 with autonomously functioning nodules, a T3 level must be measured to rule out T3 toxicosis if the T4 level is normal. After a radioiodine scan demonstrates that the toxic thyroid adenoma collects more radioiodine than the surrounding tissue, independent function is documented by failure of the autonomous nodule to decrease its iodine uptake during exogenous T3 administration. 

Blockers are usually used as adjunctive therapy with antithyroid drugs, RAI, or iodides when treating Graves disease or toxic nodules in preparation for surgery or in thyroid storm. /3-Blockers are primary therapy only for thyroiditis and iodine-induced hyperthyroidism. 

III.b.1.6. Radioactive iodine. Radioactive iodine (Iodine-131) is a radioactive isotope of iodine, usually taken in an oral solution formulation as sodium 1. Given orally as sodium I, radioactive iodine is rapidly absorbed, concentrated and stored in the thyroid follicles. The therapeutic effect depends on beta-ray emission and destruction of thyroid parenchyma manifests some weeks after treatment. It is relatively safe, cheap, painless and avoids side effects associated with surgery. It is widely regarded as the treatment of choice in adults with toxic multinodular goiter, toxic nodule and people who relapse after a course of antithyroid medication. 

Surgery is usually a near-total thyroidectomy, with main indications being suspected coexistent thyroid carcinoma, solitary toxic nodule, large goiter, failed medical treatment, patient preference and occasionally in pregnancy if adverse effects from antithyroid dmgs occur. 

Q7 In addition to Graves disease, the overactivity of one or more nodules in the thyroid can cause toxic multinodular goitre. An acute inflammation of the thyroid gland can also lead to thyroiditis, which produces a transient thyrotoxicosis. 

The ideal patient for application of radioactive iodine is therefore one who harbors a single toxic adenoma and shows a suppressed TSH (Table 81.3). Under these conditions, the surrounding healthy thyroid tissue is least affected and the patient leaves the therapy with a high chance of eliminating the overactive hyperfunctioning nodule and, at the same time, preserving the healthy tissue to resume normal thyroid function (Diedein et ai, 2004 Huysmans et aL, 1997 Reiners and Schneider, 2002 Sarkar, 2006). 

Before ultrasound-guided fine-needle aspiration came into use, scintigraphy was believed to be the most important test for the evaluation of nodules in the thyroid gland. Scintigraphy should, however, still be used when the patient with a nodule has low serum thyroid-stimulating hormone (TSH) value, to confirm the diagnosis of a toxic adenoma. 

Autonomous secretion of thyroid hormones by toxic nodules or adenomas of the thyroid gland. 

Over 200 patients have been studied by the in-vivo technique, but for the purpose of this report only those whose diagnosis has been confirmed surgically or otherwise will be reported. These include (1) normal thyroids, (2) thyroglossal cysts, (3) thyroid cancer, (4) benign solitary cold nodules, (5) functioning nodules, (6) diffuse toxic goitre, (7) flooded iodine pool. 

XRF scanning of the thyroid very clearly demonstrates this differentiation in human glands (10).. The classical heterogeneity of simple goiter as seen upon scintiscans, already by itself a reflection of the phenomenon, is also found by XRF, but not necessarily with comparable distribution.. Some non-toxic hot nodules contain non detectable amounts of stable iodine (Figure 1).. 

On the other hand, some toxic nodules present with a high amount of ITI (Figure 2) and some do not. The fact that most cancerous lesions of the thyroid contain less iodine has been demonstrated in vivo by XRF (24,25,26) ... 

In the presence of thyroid disease, and in areas with endemic iodine deficiency, suddenly raising daily iodine intake may precipitate hyperthyroidism, and this has been the subject of some concern as salt iodization efforts proceed with fledgling quality assurance. This effect is felt to be related in part to autonomous nodules in the gland that synthesize and release excess thyroid hormone. The exact prevalence of iodine-induced hyperthyroidism in deficient areas is not clear. Many coim-tries initiating salt iodization programs have reported increases in the incidence of toxic nodular goitre and iodine-induced thyrotoxicosis, usually in older people. While this may be a significant clinical problem, the risk is estimated to be between 0.01 and 0.06% and must be... 

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