Toxic thyroid nodules
How are toxic nodules detected
Some thyroid nodules release too much thyroid hormone, causing hyperthyroidism (overactive thyroid). Unlike normal nodules, these nodules lose the ability to modulate the release of thyroid hormone in response to increasing levels in the bloodstream and are therefore called “toxic”, “autonomous” or “hyperfunctioning” thyroid nodules.
Toxic nodules may be found during the evaluation of symptoms of hyperthyroidism, such as palpitations, tremor of the hands, intolerance of heat, or unintentional weight loss. Some patients do not have these symptoms and hyperthyroidism on routine lab testing can also lead to the discovery of a toxic nodule.
What is the usual evaluation of a toxic thyroid nodule?
When a toxic nodule is suspected, a thyroid uptake scan is used to confirm the diagnosis. This test measures how much iodine is taken up by the nodule compared to the rest of the thyroid. Normally, iodine enters the thyroid evenly throughout the gland. When a toxic nodule is present, most of the iodine goes into the nodule and the rest of the thyroid takes in less iodine. This difference can be seen on the thyroid scan.
Single toxic nodules are usually referred to as “toxic nodules” and sometimes as ‘toxic adenomas.’ When multiple toxic nodules are present, the term ‘toxic multinodular goiter’ is sometimes used.
Fortunately, most toxic nodules are non-cancerous. When the nodule does not have an unusual appearance and a thyroid uptake and scan confirm that a nodule is indeed hyperfunctioning, these nodules are considered benign and a biopsy is not usually needed. One important exception is when thermal ablation such as RFA, is planned. A needle biopsy is still usually necessary before thermal ablation, even for otherwise benign appearing toxic nodules.
When should toxic nodules undergo treatment?
Most toxic nodules require treatment to prevent the consequences of hyperthyroidism, such as heart rhythm abnormalities or bone loss that can cause osteoporosis. There are several treatment options available for hyperthyroidism: medications, surgery, radioactive iodine (RAI), or minimally invasive ablative therapy.
What are the treatment options for toxic nodules?
Anti-thyroid medications such as methimazole can be used to treat toxic nodules and can effectively control hyperthyroidism by lowering thyroid hormone levels. Since this treatment does not cure the disease, the medication needs to be continued long-term without interruption. For this reason, a permanent treatment is often preferred for toxic nodules.
Surgery to remove the part of the thyroid that contains the toxic nodule is curative. However, even when treatment requires that only half of the thyroid is removed, the remaining thyroid may not produce enough thyroid hormone resulting in hypothyroidism in 20-30% of cases. The resulting hypothyroidism (underactive thyroid) may require daily lifelong thyroid hormone supplementation.
Radioactive iodine ablation involves taking a pill that destroys the toxic nodule over several weeks to months. It is an effective treatment but has several drawbacks. These include treatment failure that would require a second treatment, the destruction of normal thyroid in addition to the overactive nodule which can cause hypothyroidism (not enough thyroid hormone), and radiation exposure. Radioactive iodine ablation cannot be used if you are pregnant, planning to become pregnant within 6 months, or breastfeeding.
Radioactive iodine ablation involves taking a pill that destroys the toxic nodule over several weeks to months. It is an effective treatment but has several drawbacks. These include treatment failure that would require a second treatment, the destruction of normal thyroid in addition to the overactive nodule which can cause hypothyroidism (not enough thyroid hormone), and radiation exposure. Radioactive iodine ablation cannot be used if you are pregnant, planning to become pregnant within 6 months, or breastfeeding.
A minimally invasive treatment like RFA, is another permanent treatment for toxic nodules and has several benefits over other types of therapy. Minimally invasive methods typically do not require general anesthesia and will not leave a permanent scar. There is no radiation exposure, and the risk of hypothyroidism is very low. Complete normalization of thyroid function after a minimally invasive therapy may not occur for several weeks but antithyroid medications can often be stopped immediately after treatment. The main concern for RFA as a treatment for toxic nodules is that larger nodules may be incompletely treated, resulting in persistent hyperthyroidism. If the hyperthyroidism persists after RFA, you may require retreatment and may not be able to stop anti-thyroid medications.
