What is a toxic adenoma?

A toxic adenoma is a disorder that may develop when there is growth of a thyroid nodule that produces and secretes excess amounts of thyroid hormone. By definition, this type of thyroid nodule is benign. There is no risk that the follicular cells in a toxic adenoma will spread to invade other parts of the neck or the body. As the follicular cells in a toxic adenoma divide and expand, they gradually begin to escape from the normal control exerted by the pituitary gland. This process continues until these follicular cells reach a point where they are considered to be autonomously functioning, producing and secreting thyroid hormone in an uncontrolled manner. If the amount of thyroid hormone secreted by these follicular cells exceeds normal requirements, a patient may present with evidence of hyperthyroidism or subclinical hyperthyroidism. Toxic adenomas account for about 2% of all cases of hyperthyroidism in the United States. They may develop at any age, though most patients who present to attention are between 30 and 60 years of age. Toxic adenomas are 5-15 times more common among women.

How are toxic adenomas diagnosed?

Patients who are diagnosed with toxic adenomas usually present to attention in one of two ways. Some patients may present with a visible thyroid nodule that may have been noted by observers, identified on physical examination, or discovered as an incidental finding on radiographic images of the neck. Subsequent thyroid function tests may confirm the presence of thyrotoxicosis, raising the suspicion that the thyroid nodule may represent a toxic adenoma. Other patients may present with profiles of symptoms and thyroid function tests that are consistent with thyrotoxicosis. Subsequent physical examination may reveal the presence of a thyroid nodule that may represent a toxic adenoma. In either case, further evaluation to establish a diagnosis usually involves performing a thyroid scan to generate images of the thyroid nodule in question. Thyroid nodules that represent toxic adenomas usually appear as clearly contrasting dark spots on thyroid scan images.

How are toxic adenomas treated?

Toxic adenomas may be treated with antithyroid drugs, thyroid surgery, or radioactive iodine therapy. Antithyroid drugs may effectively control hyperthyroidism associated with a toxic adenoma by inhibiting the production of excess amounts of thyroid hormone. This approach usually does not represent a long-term solution, as underlying hyperthyroidism is likely to recur soon after antithyroid drugs are stopped. Thyroid surgery may be performed to selectively remove a toxic adenoma while leaving the remainder of the thyroid gland undisturbed. This is usually a definitive form of treatment, as a toxic adenoma is unlikely to recur if it is completely removed. Radioactive iodine may be used to destroy a toxic adenoma. This unique form of treatment takes advantage of the fact that the suppression of TSH levels in the setting of hyperthyroidism associated with a toxic adenoma inhibits the uptake of iodine in the remainder of the thyroid gland. As a result, radioactive iodine administered in therapeutic doses is selectively taken up by the follicular cells in the toxic adenoma. This helps to protect the remainder of the thyroid gland.